A dinoflagellate exploits toxins to immobilize prey
prior to ingestion
Jian Shenga,1, Edwin Malkielb, Joseph Katzb, Jason E. Adolfc, and Allen R. Placed
a
Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, MN 55455; bDepartment of Mechanical Engineering, The Johns Hopkins
University, Baltimore, MD 21218; cDepartment of Marine Science, University of Hawaii, Hilo, HI 96720; and dCenter of Marine Biotechnology, University of
Maryland Biotechnology Institute, Baltimore, MD 21202
Edited by J. Woodland Hastings, Harvard University, Cambridge, MA, and approved December 11, 2009 (received for review October 29, 2009)
Toxins produced by the harmful algal bloom (HAB) forming,
mixotrophic dinoflagellate Karlodinium veneficum have long been
associated with fish kills. To date, the perceived ecological role for
toxins has been relief from grazing pressures. Here, we demonstrate that karlotoxins also serve as a predation instrument. Using
high-speed holographic microscopy, we measure the swimming
behavior of several toxic and nontoxic strains of K. veneficum and
their prey, Storeatula major, within dense suspensions. The selected
strains produce toxins with varying potency and dosages, including
a nontoxic one. Results clearly show that mixing the prey with the
predatory, toxic strains causes prey immobilization at rates that are
consistent with the karlotoxins’ potency and dosage. Even prey cells
that continue swimming slow down after exposure to toxic predators. The swimming characteristics of predators vary substantially in
pure suspensions, as quantified by their velocity, radii of helical
trajectories, and direction of helical rotation. When mixed with prey,
all toxic strains that are involved in predation slow down. Furthermore, they substantially reduced their predominantly vertical migration, presumably to remain in the vicinity of their prey. Conversely,
the nontoxic control strain does not alter its swimming and does not
affect prey behavior. In separate experiments, we show that exposing prey to exogenous toxins also causes prey immobilization at
rates consistent with potency. Clearly, the toxic predatory strains
use karlotoxins as a means of stunning their prey, before ingesting
it. These findings add a substantiated critical understanding for why
some HAB species produce such complex toxin molecules.
digital holographic microscopy
harmful algal blooms
| karlotoxin | predator–prey interactions |
M
arine dinoflagellates produce a diverse suite of complex
toxins (1, 2), yet their biological raison d’etre remains
enigmatic. Among this group, Karlodinium veneficum is a small
(∼8–12 μm) athecate phytoplankton, common in coastal aquatic
ecosystems (3–5). It has a mixed nutritional mode, relying on both
photosynthesis and phagotrophy for growth (mixotrophy). It is
frequently present in relatively low cell abundance (102–103
cells·mL−1), but is capable of forming intense blooms of 104–105
cells·mL−1 that have been associated with fish kills (6–8). Karlotoxins (KmTxs, see description in SI Section S1.1 and Fig. S1),
which are produced by K. veneficum (9, 10), generate pores in
membranes with sterols (11) and increase the ionic permeability
of cell membranes, resulting in membrane depolarization, disruption of motor functions (6), osmotic cell swelling, and lysis (SI
Section S1.3). These measured effects have been based on
purified toxins (Fig. S2). Karlotoxin type and cell quota vary with
K. veneficum strain (5), culture conditions (12), and geographic
location (5). Along the U.S. East Coast, K. veneficum strains
from south of the Chesapeake Bay produce karlotoxin 2 (KmTx2), whereas those from within the Bay produce karlotoxin 1
(KmTx-1). The hemolytic potency of KmTx-1 is 10-fold stronger
than that of KmTx-2, and toxicity increases with toxin cell quota
(5). Roles of karlotoxins have been conjectured to mediate
grazing pressures and as an allelochemical (13, 14). However, on
the basis of field data showing that cryptophyte’s abundance
2082–2087 | PNAS | February 2, 2010 | vol. 107 | no. 5
precedes K. veneficum blooms (15) and laboratory feeding
experiments demonstrating that only toxic strains are mixotrophic (16, 17), Adolf et al. (14–17) hypothesized that karlotoxins provide advantages in prey capture. Here, we investigate
whether and how karlotoxins are used during predation by
measuring changes in swimming behavior of predators and prey.
Using high-speed cinematic digital holographic microscopy
(DHM), we characterize the three-dimensional motion of several K. veneficum strains and their cryptophyte prey, Storeatula
major. As described briefly below, and in more detail in Sheng
et al. (18), this method enables us to obtain simultaneous data on
3D swimming of thousands of cells in dense suspensions of
50,000–100,000 cells/mL that have substantial depth (e.g., 3 mm,
∼300 cell lengths). In mixtures, predators and prey cells are
distinguished on the basis of their different shape and size. The
black and gray tracks in Fig. 1 A and B are sample composite
time series of in-focus images of S. major cells (only) shortly and
5 h after mixing them with predators, respectively. Note that
each track consists of a series of (one of five) in-focus reconstructed DHM images over the entire depth of the sample volume. Samples of these S. major trajectories are also highlighted
in green, to demonstrate the complexity of their swimming.
When tracks are straight, the cells are not swimming, and consequently are advected, mostly vertically, by the background flow
(which is subtracted when the swimming velocity is calculated).
In addition, we also superimpose a few complex and representative trajectories of motile K. veneficum cells in red. Additional characteristic trajectories of the K. veneficum strains
examined in this study, demonstrating the complexity of their
helical trajectories (consistent with prior observations, ref. 19),
are provided in SI Section S2, Fig. S4) and in ref. 18.
We show that in the presence of all toxic K. veneficum strains,
S. major cells slow down and become immobilized (Fig. 1, details
follow) at rates that are consistent with potency and cell toxin
quotas. Additional experiments involving purified toxins confirm
that these effects are a result of exposure to toxins (SI Section
S3). To facilitate predation of immotile prey, toxic K. veneficum
cells reduce their vertical migration and slow down in the presence of prey. In contrast, mixing of S. major and a nontoxic (and
nonpredatory) strain of K. veneficum does not alter the swimming characteristics of either organism. Clearly, karlotoxins are
mediating this behavioral change in prey.
Author contributions: J.S., E.M., J.K., and A.R.P. designed research; J.S., E.M., J.K., and J.E.
A. performed research; J.S., J.K., and A.R.P. analyzed data; and J.S., J.K., and A.R.P. wrote
the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Freely available online through the PNAS open access option.
1
To whom correspondence should be addressed at: University of Minnesota, 110 Union
Street SE, Minneapolis, MN 55455. E-mail: sheng013@umn.edu.
This article contains supporting information online at www.pnas.org/cgi/content/full/
0912254107/DCSupplemental.
www.pnas.org/cgi/doi/10.1073/pnas.0912254107
Swimming Behavior of Predators. Four strains of K. veneficum (7,
17) with identical genetic signatures (internal transcribed spacer
sequence), two from Chesapeake Bay (MD5 and CCMP 1974)
and two from estuaries south of Chesapeake Bay (BM1 and
CCMP 2064), were examined. MD5 produces no detectable
toxin and shows no mixotrophic behavior (15). Of the rest, 1974
produces KmTx-1 (0.3 pg/cell), whereas BM1 and 2064 produce
KmTx-2 in a cell quota ranging from 1 to 2 pg/cell (5). The longterm ingestion rates of prey by the toxic strains decrease slightly
in the order 1974 > BM1 > 2064 (15). We quantify the swimming
of all of the above-mentioned organisms before, shortly after,
and 5 h after mixing, along with effects of purified toxins without
predator on S. major swimming.
Fig. 2 contains a series of joint probability distribution functions (PDF) that characterize the swimming behavior of various
cells on the basis of velocity magnitude and radius of their helical
trajectories, as illustrated in Fig. 2A. Corresponding ensemble
averaged velocities, radii, and angular velocities are also summarized in Table 1. Each data point provides the mean value and
its SD, the latter demonstrating the extent of variability in the
statistics over time and among individual cells. As summarized in
Table S1, the uncertainty in mean statistics, as estimated using
the bootstrap method, is ∼1%. Each section of Fig. 2 also shows
the total number of tracks analyzed to obtain the specific PDF,
along with the fraction of cells that are motile. Only motile cells
are included in characterization of swimming. Fig. 2B presents
the K. veneficum swimming statistics, the Top row before mixing
with S. major, the Middle row shortly after mixing, and the Bottom row 5 h later. As is evident, in isolation, swimming velocity
and helix radius of K. veneficum vary substantially among strains.
Both MD5 and BM1 swim in left- and right-handed helices,
whereas 1974 and 2064 are preferentially right-handed, with
small fractions performing left-handed maneuvering at low
speed. It should be noted here that unlike previous observations,
in which dinoflagellates swam only in right-handed helices, e.g.,
ref. 20, two of the present strains are almost equally likely to
swim in left-hand and right-hand trajectories.
Nontoxic K. veneficum MD5 shows no change in swimming
behavior upon introduction of S. major for up to 5 h. Thus, we
use it as a control for noninteracting species. Conversely, PDFs
Sheng et al.
of 1974 (Fig. 2B, second and third rows) become bimodal, with
one peak at low speed and small radius and the other at high
speed and large radius. Of the low speed cells, 37 (38%) of the
98 tracked are located near, or connected to, a prey, i.e.,
appearing similar to the BM1 and prey cell in Fig. 1C, indicating
that successful feeding commences immediately. Those that are
not located very close to prey are positioned within five body
lengths. On the basis of nearest neighbor distance PDFs (SI
Section S4 and Fig. S5), the 1974 cells that continue swimming
fast have a slight tendency toward being located near prey in
comparison with randomly distributed cells. Initially, both
KmTx-2 strains slow down appreciably in response to introduction of prey. However, very few (9%) start immediately
feeding. After 5 h, 60% of the BM1 cells still swim, mostly in
right-handed helices and at 83% of prepredation speeds (Table
1). Of them, 18%, mostly slow ones, are feeding (e.g., Fig. 1 C
and D). A few immotile cells are also actively ingesting. The 2064
strain follows the same trend, but with different percentages
(14%). Nearest neighbor distance statistics for 2064, presented
in ref. 18, reveal that predator and prey cells are randomly distributed relative to themselves, but in a mixed culture, predators
are preferentially clustered around prey cells.
Furthermore, ensemble averaged Lagrangian autocorrelation
functions for each velocity component (Material and Methods
and SI Section S5), whose time integral is the swimming-induced
dispersion rates, Dii (21–23), show conclusively (Table 1) that in
the phototrophic mode, all strains preferentially spend more
energy in vertical migration (Fig. S6), as compared to horizontal
motions. This trend monotonically decreases with increasing
toxicity. Visually, helices of all strains are preferentially aligned
vertically, as shown in Fig. 1 and Fig. S4. The implication is that
assemblages would spread vertically faster than horizontally.
Introduction of prey reduces the dispersion rates of all toxic
strains (Fig. S7). In two cases, 1974 and BM1, the ratio of vertical
to horizontal diffusion also decreases, by 20 and 27%, respectively, but preference toward vertical migration largely remains
(see red trajectories in Fig. 1 for BM1), especially for 2064.
Response of Prey to Predators and Purified Karlotoxins. Before
mixing with predators, motile S. major cells swim in both leftPNAS | February 2, 2010 | vol. 107 | no. 5 | 2083
ECOLOGY
Fig. 1. Superposition of reconstructed in-focus holographic images (only one of every five exposures is shown for clarity). Gray trajectories, tracks of prey, S.
major (only) after introduction to a K. veneficum, BM1 suspension; green, highlighted samples of S. major trajectories; red, a few samples of K. veneficum
BM1 (predator) trajectories. (A) Shortly after mixing; (B) 5 h later; (C and D) captured S. major cells (smaller ones) being ingested by a BM1 cell, (C) a
reconstructed hologram and (D) SEM. (E and F) A pair of K. veneficum, BM1 cells interacting (possibly cell division): (E) reconstructed hologram, (F) SEM.
Vertical linear tracks belong to immotile prey; convection by the background flow causes their linear motion, which is subtracted while calculating velocity.
(Scale bars: A and B, 100 μm; C and E, 5 μm.) The complex motions of motile cells and increasing fraction of immotile ones with time are evident.
Fig. 2. Joint probability density functions (PDFs) of velocity magnitude (V) and radius of helical trajectories (R). (A) Sample trajectory of a BM1 cell, color
coded with velocity magnitude. Only one of every four frames is shown for clarity. In this example, the cell slows down at the end of the time series, when it is
located very close to a prey. (Inset) Definitions of velocity, radius of a helix, and angular velocity quantifying the 3D motion of dinoflagellates. (B) Several
strains of the dinoflagellate K. veneficum before (Top), shortly after (Middle) and 5 h after (Bottom) introducing them to prey (S. major). R < 0 and R > 0
indicate left-handed and right-handed helices, respectively. Total number of analyzed motile (only) K. veneficum tracks and their fractions of the total K.
veneficum population are shown. (C) Response of S. major, swimming velocity and helix radius, before and shortly after introducing them to several K.
veneficum strains, as indicated above each frame. Numbers in frames: Upper Left, the total number of analyzed tracks of motile cells and their fraction of the
total S. major population; Upper Right, average total number of S. major cells in the sample volume during the test. (D) Response of S. major 5 h after
exposure to low-concentration exogenous karlotoxins. Numbers in frames: same as in C. (E) A sample image showing a KmTx-1-producting strain 1974
capturing a cryptophyte prey. The prey cell is evidently swollen from its original size of 6–8 μm to 10 μm.
and right-handed helices. The PDF (Fig. 2C, left panel) shows a
fraction swimming at high speed and another significant group
moving slowly. We quantify the response to toxic strains on the
basis of both changes in swimming behavior (Fig. 2C and Table
1) and the fraction of cells that become immotile (Fig. 3 and
straight tracks in Fig. 1 A and B). Statistics on clearance rate, i.e.,
the rate of prey disappearance per predator cell, are also provided in Table 1. In the control sample, which is mixed with
MD5, all PDF peaks persist with a shift in probability toward
high speed. The immotile fraction remains unchanged, at ∼30%.
Conversely, exposures to toxic strains and purified toxin extracts,
the latter shown in Fig. 2D, substantially reduce the speed of
motile cells and increase the fractions of cells that become
immobilized (Fig. 3). KmTx-1-producing strains cause an
immediate reduction in velocity of motile cells (by >50%, see
Table 1), and a substantial increase in the fraction of immotile
ones, from 31 to 54%. In 2.5 ng·ml−1 extracts of this toxin, a
small quantity that would be generated by ∼1,000 cells·ml−1,
52% become immobile immediately and >90% 5 h later. During
2084 | www.pnas.org/cgi/doi/10.1073/pnas.0912254107
exposure to this toxin, as illustrated by the sample microscopic
image presented in Fig. 2E, the prey (left, orange one) swells
from its original 6-μm size to ∼10 μm. Note that because the
exogenous toxin is water insoluble, it is dissolved in methanol
and then mixed with the culture. Whereas the karlotoxins are
fully recoverable upon addition to media, once cryptophytes are
added, the toxins become undetectable. To rule out the effect of
carrier addition, we have also measured the motility of S. major
cells in the same concentration of pure methanol (Fig. 2D, second panel). As is evident, the exogenously added methanol has
little effect on the prey’s motility.
Short-term responses to KmTx-2 strains are much weaker, and
levels are consistent with toxin quotas produced by the predators.
In a BM1 suspension, S. major slows down by ∼25%, but there is
no appreciable change in its motility fraction initially. In the
presence of 2064, behavior modifications are mild. Five hours
later, the velocity of swimming S. major cells is lower than control values by 20–25% for both KmTx-2 cases, and the fraction of
immotile cells almost doubles, to 55 and 59% in BM1 and 2064
Sheng et al.
Table 1. Summary of motilities of motile K. veneficum and S. major
Strain
V ± σV
(μm·s−1)
R ± σR
(μm)
S. major
MD5
81.3 ± 44.9 4.57 ±
MD5 + S. major (h0) 84.5 ± 48.6
4.6 ±
MD5 + S. major (h5) 82.3 ± 50.1
4.7 ±
1974
102.3 ± 56.4
9.2 ±
1974 + S. major (h0) 160.4 ± 59.6 16.2 ±
BM1
111.2 ± 55.15 9.3 ±
BM1 + S. major (h0)
81.8 ± 55.5
6.5 ±
BM1 + S. major (h5)
92.7 ± 43.6
8.7 ±
2064
80.9 ± 38.9
6.5 ±
2064 + S. major (h0) 37.8 ± 40.1 3.76 ±
2064 + S. major (h5) 59.4 ± 35.1
4.7 ±
S. major +
methanol (h5)
S. major + KmTx-1,
2.5 ng·mL−1 (h5)
S. major + KmTx-2,
2.8 ng·mL−1 (h5)
ω ± σω
(rad·s−1)
4.9 6.98 ± 3.7
5.3 6.9 ± 2.2
5.1 6.8 ± 3.0
8.6 5.67 ± 2.9
5.7 8.7 ± 6.1
8.8 6.7 ± 3.1
7.4 6.4 ± 3.0
7.5 5.6 ± 2.7
6.8 5.0 ± 2.7
5.0 6.8 ± 3.8
5.1 5.5 ± 3.0
S. major (motile)
Dzz/
ν
Dzz/Dii
(i = x, y)
2.67
2.51
2.57
1.01
0.85
2.05
1.15
1.28
0.78
0.64
0.61
9.1
8.9
9.0
2.0
1.6
2.6
2.0
2.5
3.2
3.1
3.1
Clearance
rate (no.
cells−1·h−1)
V ± σV
(μm·s−1)
R ± σR
(μm)
ω ± σω
(rad/s)
Dzz/
ν
Dzz/Dii(i
= x, y)
86.4 ± 47.0
5.8 ± 6.1
7.3 ± 4.0
0.45
1.8
85.2 ± 46.1
86.8 ± 40.1
5.1 ± 5.9
6.1 ± 4.8
7.2 ± 3.8
7.8 ± 2.5
0.45
0.45
1.9
1.7
0.03 ± 0.12
42.7 ± 37.7
2.9 ± 4.3
8.1 ± 4.1
0.28
1.5
0.39 ± 0.13
65.1 ± 41.9
69.8 ± 44.6
4.1 ± 4.8
5.1 ± 6.0
6.9 ± 3.2
6.7 ± 3.3
0.45
0.5
6.3
1.7
0.36 ± 0.06
81.7 ± 44.4
63.2 ± 41.4
78.85 ± 29.7
4.7 ± 5.2
6.9 ± 3.5 0.72
4.2 ± 5.6
6.4 ± 3.0 0.25
3.58 ± 3.63 6.51 ± 2.92
4
1.4
0.30 ± 0.11
60.77 ± 36.7
3.09 ± 3.03 7.92 ± 3.56
70.3 ± 28.44 5.17 ± 4.74
5.7 ± 4.3
The mean and SDs of swimming are characterized by velocity (V), helical radius (R), and helical angular velocity (w) that indicates the speed of an organism
completing a helical full circle. Swimming-induced dispersion coefficients (Dii, i = x, y, z) are computed using autocorrelation functions of swimming velocity
components. The dispersion coefficient associated with the preferred vertical direction, Dzz, normalized with kinematic viscosity of seawater at 20 °C, ν =
1.05 × 10−6 m2s−1, suggests that swimming organisms disperse at the same rate as the momentum diffusion of background flow. The preferences of vertical
dispersion by difference strain are indicated by the ratio between vertical component and the mean of horizontal directions. h0, immediately after
introducing prey; h5, 5 h after introducing prey. The bottom three rows present the motilities of S. major 5 h after they were exposed to low dosage
exogenous karlotoxins. Clearance rate is defined as the number of prey cells that disappeared per predator cell per time.
suspensions, respectively. In 2.8 ng·ml−1 KmTx-2 toxin extract,
70% become immotile after 5 h. Figure 1 A and B provides a
striking graphical demonstration of the decreased fraction of
motile S. major cells with time. Whereas very few tracks are
straight shortly after mixing the prey with KmTx-2-producing
predator, 5 h later, most of the S. major cells are immobile. Also,
Fig. 3. Fraction of immotile cells in suspensions before, shortly after mixing
predator and prey, and 5 h later, as well as fraction of immotile prey cells 5 h
after exposure to exogenous karlotoxins and toxin solvent. (Upper) K. veneficum strains; (Lower) S. major. (Left) S. major and K. veneficum mixtures;
(Right) S. major exposed to exogenous karlotoxins and solvent alone. Error
bars: SD of instantaneous data from the time average (mean values that
deviate by more than twice the SD are significantly different at the 5%
confidence level). Many of the immotile prey cells are attached to predator
cells. Substantial fractions of S. major cells become immotile shortly after
exposure to K. veneficum 1974. In the presence of K. veneficum BM1 and
2064 the immotile fraction increases only after 5 h. 0h, immediately after S.
major is introduced; 5h, 5 h later.
Sheng et al.
in Fig. 1B, 13% of the vertical linear tracks (immotile cells)
involve attached cell pairs. Some involve a K. veneficum cell
predating on S. major, as in the magnified example and corresponding SEM image presented in Fig. 1 C and D, respectively,
but others consist of predator pairs, possibly cell division or
mating, as shown in Fig. 1 E and F.
Before mixing within the control strain, dispersion coefficients
of S. major also display preference toward vertical migration
(Table 1). The dispersion decreases immediately by ∼40% in all
directions upon exposure to the KmTx-1 strain. When mixed
with KmTx-2 strains, in both cases, the magnitude of
2Dzz =ðDxx þ Dyy Þ more than doubles initially and then returns to
premixed ratios after 5 h. Is the initial enhanced preference
toward vertical migration an “escape strategy” before the less
potent karlotoxin takes effect?
Discussion
Mixotrophy substantially enhances the growth rate of K. veneficum (SI Sections S1.4, Fig S3 and ref. 15). Here we show that
karlotoxins are a vital instrument in the predation process.
Clearly, in the presence of toxic K. veneficum strains (only), prey
cells slow down and become immobilized at rates that are consistent with phenotypic toxicity and dosage of toxins. Predation,
appearing as predator–prey attachment in holographic and
microscopic images (Movie S1), occurs concurrently with
reduction in prey motility. Exposure to the KmTx-1 strain causes
immediate reaction, whereas the response to KmTx-2 strains is
slow, but effective in a period of hours. Immobilization occurs
also when prey is introduced to toxins without predators, confirming the causality between motility reduction and presence of
toxins. Furthermore, prior studies have shown that adding
exogenous KmTx-2 (25 ng·mL−1) to feeding cultures of 2064 and
1974 enhances their ingestion efficiency by nearly 3-fold (14).
The presently measured trends in clearance rates of prey cells
PNAS | February 2, 2010 | vol. 107 | no. 5 | 2085
ECOLOGY
K. veneficum (motile)
are consistent with toxin potency and cell quota, and the actual
values agree with previously published ingestion rates by the
various strains (15). In contrast, S. major does not alter its
swimming behavior in the presence of a nontoxic strain. Whereas
few expect that harmful algal bloom (HAB) species make toxins
specifically to kill fish, fewer still have been able to demonstrate
why HABs make toxic substances in the first place. Use of KmTx
to alleviate grazing, as shown before (13), and to capture prey, as
comprehensively demonstrated here, would serve to increase the
population growth rate of K. veneficum in nature and may foster
bloom formation for this cosmopolitan species.
We caution the reader that given the substantial diversity
in dinoflagellate toxins and modes of feeding, we do not intend
to imply here that all toxins are used for predation. However,
for cases with structures that are similar to that of karlotoxin,
e.g., amphidinol (SI Section S1,1), produced by the mixotrophic
Amphidinium sp., one may hypothesize a similar role in predation. We also have not addressed the method of delivering
toxins from predator to prey. Presumably, although it is unknown
where karlotoxins are located in the cell, they must be readily
available for release because exposure to mild shear during filtration or centrifugation causes almost complete release of toxins
(10). Conversely, in pure (unforced) suspensions, 95% of the
toxin remains cell bound (10); i.e., very little is released without
stimulation. When prey is introduced, cell quotas are reduced by
>50% (SI Section S1.4 and Fig. S3), indicating release, and they
become prey bound and undetectable. Due to its low solubility, it
is reasonable to assume that the initial karlotoxin administration,
before predator and prey are connected, requires close proximity, but we do not know whether it involves direct contact. We
hypothesize why toxic K. veneficum slows down during predation
in spite of very different swimming and migration patterns in
isolation. Our argument is that once administered, there is no
advantage for the predator to leave the proximity of an intoxicated prey that is in the process of being immobilized.
Materials and Methods
Materials. All strains were maintained phototrophically as unialgal cultures in
15 ppt ESAW culture medium as described (5). On the day of observations (7
h into the light period), equal volumes of K. veneficum strains and S. major
cells were mixed to give a starting cell density of 35,000 cells·mL−1 and
predator to prey ratio of 2.5. All experiments were performed with laboratory ambient lighting, and samples were returned to a lit incubator
between observations. Because K. veneficum does not ingest cryptophytes
or grow when maintained in the dark for several days (17), suggesting that
this organism is an obligate phototroph, we opted to perform the measurements during the light phase of the normal photoperiod. Holograms
were recorded for 20 s before mixing predators with prey, shortly after
mixing, and 5 h later. The cells were also observed under a microscope to
confirm feeding.
with a volume of <6 μL of purified KmTx1-1 stock, (25 or 250 μg·mL−1) were
added to a 1-mL S. major aliquot to produce toxin levels between 50 and
1,000 ng·mL−1. For each exposure to KmTx1-1, the same volume of MeOH
(carrier) was added to a control. Samples were monitored in the ToxY PAM
fluorometer and the percentage of PSII inhibition (relative to control) was
recorded after 10 min, using ToxYWin software. Samples were then immediately diluted 10-fold and analyzed on a Coulter Multisizer II for cell abundance and diameter. A swelling index was calculated for each exposure as the
cell diameter of the experimental treatment divided by the diameter of the
control. Solutions of purified (10) karlotoxins (KmTx-1–3 and KmTx-2) in
methanol at concentrations of 2.5, 25, and 250 ng·mL−1 for KmTx-1–3 and 2.8,
28, and 280 ng·mL−1 for KmTx-2, were prepared. These exogenous concentrations correlate to ≈103–106 cells·mL−1. Swimming of S. major after toxin
addition and toxin concentrations were monitored after 0.25, 2.5, and 5 h.
DHM Setup and Analysis. Measurements were performed using in-line, cinematic (120 frames/s) digital holographic microscopy (18, 24, 25), using the
optical setup described in ref. 18. The sample volume was illuminated by a
collimated He-Ne laser beam (red, 0.6328-μm wavelength), and holograms
magnified at 20× were recorded on a 1,024 × 1,024 pixels camera, at a
resolution of 0.975 μm/pixel. The samples were placed in a 3 × 3 cross section, 40-mm high cuvette, and the sample volume was 0.8 × 0.8 × 3 mm, the
latter being the depth. Digital reconstruction and analysis in-house developed software enabled simultaneous tracking of the particle within each
suspension. Predator and prey cells were distinguished on the basis of their
shape and size by examining in-focus images of each track. Velocity and
helix radius were computed from the 3D position vector, !
r ðtÞ, using
j!
e r_ × ð!
e €r × !
e_ =j!
e_ jÞj
pffiffiffiffiffiffiffiffiffiffiffiffiffiffi€r ffi €r ;
k2 þ τ2
!
!
!
_
!
_
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
e r_ ·ð e €r × e €r =j e €r jÞ
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
; jωj ¼ V ðtÞ k2 þ τ2 ;
P¼
2
2
k þτ
3
€_
€_
€_
k ¼ j!
r_ × !
r _ ·ð!
r€ × !
r j=!
r_ ; τ ¼ !
r Þ=j!
r_ × !
r j2
V ðtÞ ¼ j!
r _ ðtÞj; R ¼
where !
e is a unit vector aligned with the vector indicated in the subscript,
the number of dots indicates order of time derivatives, k is radius of curvature, and τ is torsion. Further details along with associated uncertainties
are provided in supporting information in ref. 18. Using extensions to Taylor’s theory for scalar and particle diffusion (21–23, 26), swimming-induced
dispersion coefficients were determined from an ensemble average of the
Lagrangian autocorrelation function of particle velocity:
Dii ðtÞ ¼
ðt
τ¼0
ð∞
dξ
η¼0
hui ðηÞui ðη þ ξÞidη
Here, ξ and η are time, ui is the fluctuating component of velocity component, and Ææ denotes ensemble averaging over trajectories of the same
species. The asymptotic value of Dii ðtÞ yields the Fickian diffusion coefficient.
Exposure to Purified Toxins. To measure effects of purified karlotoxin on
cryptophyte cells, an exponential phase culture of S. major (15 ppt ESAW
culture medium) was diluted to 35,000 cells·mL−1. The PSII inhibition assay
was conducted on 1-mL aliquots held in the cuvette of a ToxY PAM dual
channel photosynthesis analyzer (Heinz Walz). In independent, paired assays
ACKNOWLEDGMENTS. J.S. was supported by National Science Foundation
CAREER Award CBET-0844647; the Johns Hopkins University group was
funded in part by Grants CBET-0625571 and OCE-0402792 (to J.K.) from the
National Science Foundation; and the Center of Marine Biotechnology
group was supported in part by Grants NA04NOS4780276 from the National
Oceanic and Atmospheric Administration Coastal Oceans Program and EF0626678 from the National Science Foundation (to A.R.P.). This is contribution 10-212 from the Center of Marine Biotechnology.
1. Kobayashi J, Kubota T (2007) Bioactive macrolides and polyketides from marine
dinoflagellates of the genus Amphidinium. J Nat Prod 70:451–460.
2. Murata M, Yasumoto T (2000) The structure elucidation and biological activities of
high molecular weight algal toxins, maitotoxin, pyrmnesins and zoozanthellatoxins.
Nat Prod Rep 17:293–324.
3. Goshorn D, et al. (2004) In Proceedings of Harmful Algae 2002. Florida Fish and
Wildlife Commission, Florida Institute of Oceanography, and Intergovernmental
Oceanographic Commission of UNESCO, eds KA, S, JH, L, Tomas, CR, GA, V (St
Petersburg), pp 361–363.
4. Hall NS, et al. (2008) Environmental factors contributing to the development and
demise of a toxic dinoflagellate (Karlodinium veneficum) bloom in a shallow,
eutrophic, lagoonal estuary. Estuaries Coasts 131:402–418.
5. Bachvaroff TR, Adolf JE, Place AR (2009) Strain variation in Karlodinium veneficum
(Dinophyceae): Toxin profiles, pigments, and growth characteristics. J Phycol 45:
137–153.
6. Deeds JR, Reimschuessel R, Place AR (2006) Histopathological effects in fish exposed
to the toxins from Karlodinium micrum (Dinophyceae). J Aquat Anim Health 18:
136–148.
7. Kempton JW, Lewitus AJ, Deeds JR, Law JM, Place AR (2002) Toxicity of Karlodinium
micrum (Dinophyceae) associated with a fish kill in a South Carolina brackish
retention pond. Harmful Algae 1:233–241.
8. Deeds JR, Terlizzi DE, Adolf JE, Stoecker DK, Place AR (2002) Toxic activity from
cultures of Karlodinium micrum (=Gyrodinium galatheanum) (Dinophyceae) - a
dinoflagellate associated with fish mortalities in an estuarine aquaculture facility.
Harmful Algae 1:169–189.
9. Van Wagoner RM, et al. (2008) Isolation and characterization of karlotoxin 1, a new
amphipathic toxin from Karlodinium veneficum. Tetrahedron Lett 49:6457–6461.
10. Bachvaroff TR, Adolf JE, Squier AH, Harvey HR, Place AR (2008) Characterization and
quantification of karlotoxins by liquid chromatography-mass spectrometry. Harmful
Algae 7:473–484.
2086 | www.pnas.org/cgi/doi/10.1073/pnas.0912254107
Sheng et al.
18. Sheng J, et al. (2007) Digital holographic microscopy reveals prey-induced changes in
swimming behavior of predatory dinoflagellates. Proc Natl Acad Sci USA 104:
17512–17517.
19. Kamykowski D (1995) Trajectories of autotrophic marine dinoflagellates. J Phycol 31:
200–208.
20. Fenchel T (2001) How dinoflagellates swim. Protist 152:329–338.
21. Taylor GI (1921) Diffusion by continuous movements. Proc Lond Math Soc 2:196–212.
22. Snyder WH, Lumley JL (1971) Some measurement of fluid-particle motion in an
isotropic turbulent field. J Fluid Mech 48:41–71.
23. Gopalan B, Malkiel E, Katz J (2008) Experimental investigation of turbulent diffusion
of slightly buoyant droplets in locally isotropic turbulence. Phys Fluids 20:095102–
095115.
24. Sheng J, Malkiel E, Katz J (2008) Using digital holographic microscopy for
simultaneous measurements of 3D near wall velocity and wall shear stress in a
turbulent boundary layer. Exp Fluids 45:1023–1035.
25. Sheng J, Malkiel E, Katz J (2009) Buffer layer structures associated with extreme wall
stress events in a smooth wall turbulent boundary layer. J Fluid Mech 633:17–60.
26. Csanady GT (1963) Turbulent diffusion of heavy particle in the atmosphere. J
Atmos Sci 20:201–208.
ECOLOGY
11. Deeds JR, Place AR (2006) Sterol specific membrane interactions with the toxins from
Karlodinium micrum (Dinophyceae) - A strategy for self-protection. Afr. J. Mar. Sci.
28:421–425.
12. Adolf J, Bachvaroff TR, Place AR (2009) Environmental modulation of karlotoxin levels
in strains of the cosmopolitan dinoflagellate Karlodinium veneficum (Dinophyceae). J
Phycol 45:176–192.
13. Adolf JE, Krupatkina D, Bachvaroff T, Place AR (2007) Karlotoxin mediates grazing by
Oxyrrhis marina on strains of Karlodinium veneficum. Harmful Algae 6:400–412.
14. Adolf JE, et al. (2006) Species specificity and potential roles of Karlodinium micrum
toxin. Afr. J. Mar. Sci. 28:415–419.
15. Adolf JE, Bachvaroff T, Place AR (2008) Can cryptophyte abundance trigger
toxic Karlodinium veneficum blooms in eutrophic estuaries? Harmful Algae 8:
119–128.
16. Adolf JE, Stoecker DK, Harding LW, Jr (2006) The balance of autotrophy and
heterotrophy during mixotrophic growth of Karlodinium micrum. J Plankton Res 28:
737–751.
17. Li A, Stoecker DJ, Adolf JE (1999) Feeding, pigmentation, photosynthesis and growth of
the mixotrophic dinoflagellate Gyrodinium galatheanum. Aquat Microb Ecol 19:163–176.
Sheng et al.
PNAS | February 2, 2010 | vol. 107 | no. 5 | 2087
Supporting Information
Sheng et al. 10.1073/pnas.0912254107
SI Text is provided in four sections. Section S1 provides background on toxins produced by K. veneficum, along with additional information on effects of these toxins on the S. major cells
and toxin cell quotas. Section S2 displays sample trajectories of
K. veneficum, and Section S3 provides statistics about bootstrap
analysis of swimming parameters. Section S4 provides nearest
neighbor distance statistics for a suspension shortly after mixing
toxic K. veneficum 1974 with S. major. Section S4 provides
background on measurements of swimming-induced dispersion
of particles/organisms, followed by data for all of the present
organisms.
S1.1: Structure of Karlotoxins and Their Effects on S. major
Cells (Fig. S1).
S1.2: Geographic Distribution of Karlotoxins. In an attempt to
determine the cause of repeated fish kills in an estuarine aquaculture facility in Maryland, K. veneficum has been shown to
produce a unique suite of compounds with hemolytic, cytotoxic,
and ichthyotoxic properties, which we refer to as karlotoxins
(KmTx) (1). Thus far, we have been able to detect these compounds in colonial isolates collected from estuarine waters from
the U.S. states of Maryland, North and South Carolina, Georgia,
and Florida (2), as well as isolates from New Zealand, Norway,
and the English Channel. In addition, we were able to isolate
these same toxins directly from water samples collected during
fish kills in a South Carolina brackish water pond (3) as well as a
fish kill in a tributary of the Chesapeake Bay. In both cases, high
densities of K. veneficum were found. The principal toxin isolated both from cultured cells and directly from water samples
collected during the fish kill in South Carolina (KmTx-2) was
similar but not identical to the main toxin isolated from cultures
and the fish kill in Maryland (KmTx-1) (Fig. S1, first vs. second
row). Hence, two different toxin types occur in Karlodinium spp.
from the U.S. Atlantic coast (2). The structures of these compounds have recently been solved (4, 5) and are remarkably
similar to the pore-forming toxin amphidinol (Fig. S1). The
mode of toxicity of these molecules involves pore formation in
membranes containing des-methyl sterols (6).
S1.3: Effects of Purified KmTx-1 on Prey (S. major) Cell Volume and
Photo-System (PSII) Efficiency. As evident in Fig. S2, concentrations
of KmTX1-1 >100 ng·mL−1 resulted in swelling of S. major
relative to controls. Maximum swelling, at ≈1.4 times the control
cell diameter, was observed during exposure to ∼200 ng·mL−1
KmTX1-1. Cell lysis was not observed at any tested concentration of KmTX1-1; in fact, cell abundance in KmTX1-1-treated
samples averaged 10% higher than controls. Concurrent with the
increase in cell volume, concentrations of KmTX1-1 >100
ng· mL − 1 caused inhibition of PSII relative to controls, with
maximum inhibition of 80–90% not being observed until
KmTX1-1 concentrations reached 500 ng · mL − 1 . The swelling
and inhibition of photosystem II are consistent with the formation of nonspecific pores by karlotoxin addition as observed
earlier for red blood cell lysis (1).
S1.4: Toxin Cell Quota During Autotrophic and Mixotrophic Growth.
An important feature of this phototrophic dinoflagellate is its
phagotrophic capability that dramatically enhances growth (7).
Field and laboratory experiments have demonstrated that K.
veneficum is able to eat a variety of other protists, including
cryptophytes, with which it commonly co-occurs in the Chesapeake Bay (8, 9). Deeds et al. (1) reported similar cell quotas
Sheng et al. www.pnas.org/cgi/content/short/0912254107
and types of KmTx between autotrophic and mixotrophic cultures of K. veneficum (CCMP 1974). Mixotrophic cultures used
for this analysis grew nearly 40% faster than autotrophic cultures, suggesting that similar cell quotas of toxin between autotrophic and mixotrophic K. veneficum involved an ≈40% higher
rate of toxin production by the mixotroph.
SI Materials and Methods. We performed a more detailed analysis of
karlotoxin cell quotas as a function of feeding mode with a single
strain (CCMP 2778) in a large culture. Cultures were grown in a
20-L polycarbonate multiport carboy that had been acid washed
(10% HCl) before addition of medium and inoculation. The
vessel was located inside a walk-in incubator room set at 20 °C.
Light was supplied on a 14:10 light:dark cycle from cool-white
fluorescent bulbs on the walls of the incubation chamber, resulting in 138 mmol photons·m−2·s−1 incident on the surface of
the vessel closest to the light (measured with a Li-Cor QUANTUM probe attached to a Li-Cor LI-250 light meter). Cultures
were bubbled with air from an aquarium pump at ≈10 bubbles
per second. CO2 levels and pH of the medium were controlled
automatically by a Pinpoint pH controller (American Marine)
that controlled a CO2 regulator with solenoid and needle valve
(CO2 Regulator Deluxe: Dual Gauge with Solenoid, www.marinedepot.com). The pH controller was set to open the valve at
pH > 8.3 and close at pH < 8.1. When open, CO2 was added
from a pure tank at a rate of 1 bubble per second. The air and
CO2 were connected with a Y-junction to a common line going
into the culture and one-way valves were placed upstream of the
Y-junction but downstream of the air and CO2 sources, allowing
flow only toward the culture. Three liters of media was added to
the 20-L multiport and was inoculated with <200 mL of algal
culture that had been acclimated to the growth chamber conditions for 1 week. Cell density was monitored at least daily using
a Coulter Counter and an aliquot was taken for karlotoxin
analysis (10). Fresh medium (11) was added to the culture by a
pump (Peristaltic Pump P-1, Amersham Biosciences) that drew
medium from a reservoir located next to the culture. The flow
rate of the pump was set to equal the growth rate of the culture
over a 24-h interval—the goal was to have no change in algal
density but rather a change in total number of cells due to an
increase in culture volume. When the multiport vessel was full,
15 L of the culture was transferred to a separate carboy for
harvesting.
To initiate feeding a previously grown culture of S. major was
added to provide a predator-to-prey ratio >5. This was repeated
for two growth cycles followed by addition of media alone to
initiate phototrophic growth for growth cycles followed by two
additional mixotrophic growth cycles.
Summary of Observations. The growth curves and associated toxin
cell quotas are presented in Fig. S3. As is evident, when growing
mixotrophically, the karlotoxin cell quotas are >50% lower than
those when growing autotrophically. This trend supports our
claim that toxins are used during predation. Furthermore,
growth rates are typically higher during mixotrophic growth
compared to those during autotrophic growth.
S2: Sample K. veneficum trajectories (Fig. S4).
S3: Bootstrap analysis of swimming statistics. Table S1 provides
results of bootstrap analysis (12) to determine the statistical
convergence of S. major swimming characteristics presented in
Table 1 in the main text. Results, summarized in Table S1, show
the 95% confidence interval. Clearly shown in Table 1, S. major
slows down when exposed to exogenous karlotoxins; however,
1 of 8
the levels of immobilization are consistent with the toxicity of
ecologically relevant toxin concentration.
S4: Nearest Neighbor Distance Analysis on Spatial Distribution of
Predators and Prey. Fig. S5 provides the probability density
function of nearest neighbor distance (NND) from motile
predators to prey cells in a suspension of K. veneficum strain
1974 and its cryptophyte prey, S. major. The PDFs characterize
the spatial structure of the suspension and the location of the
predatory organism relative to the prey cell. Shortly after the
introduction of prey S. major, a portion of K. veneficum, 1974,
swimming at an average speed of 160 μm/s, clusters around prey
(green solid in Fig. S5); meanwhile the other prominent group
associated with the low swimming motility is observed to be either already attached to or located less than two body lengths to
a prey cell (bar graph in Fig. S5). It may suggest that the population of motile predators is divided into two groups upon
mixing with prey. One group with large swimming parameters
appears to be in search of prey; and the other slowing down
drastically is evidently engaged in the process of ingesting prey.
Lagrangian velocity components along the particle trajectory; i.
e.,
ðt
ðt ð∞
Dii ðtÞ ¼ Rii ðτÞdτ ¼
ui ðηÞui ðη þ τÞdηdτ;
[S2]
τ¼0 η¼0
0
where τ is time, u is the fluctuation component of organism
velocity, and the subscript i refers to a direction, x, y, or z. Due to
the limited spatial extent of essentially all velocity measurement
systems, including DHM, the autocorrelation function can be
measured only over a finite time. Consequently, Snyder and
Lumly (18) have introduced the idea of ensemble averaging of
many particle trajectories, each with a finite length. The revised
diffusion coefficient Dii ðτÞ is thus determined from
ðt ðτ
ðt ðτ
dτ Rii ðηÞdη ¼ dτ hRii ðηÞidη;
[S3]
Dii ðtÞ ¼
0
0
0
0
∂C
¼ ∇·ðD·∇CÞ;
·∇C
þu
[S1]
∂t
is the number concentration of the organisms, u
is the
where C
mean advective velocity of the entire population, and D is the
diffusion coefficient tensor. A similar equation for chemotaxis of
bacteria with a drift velocity replacing the advection velocity has
been also proposed by Keller and Segel (13). However, modeling
diffusion processes is problematic because the scales involved are
often of the same order as the domain being investigated (14).
To determine the swimming-induced diffusion coefficients, we
apply in this paper the Lagrangian theory of diffusion, which has
been introduced by Taylor (15) to determine the diffusion rate of
a scalar in stationary, homogeneous, and isotropic turbulence
and subsequently extended by Csanady (16) to suspended particles. This theory is based upon a simplification, which leads to a
conclusion that dispersion of a particle cloud can be completely
characterized by the Lagrangian motion of individual particles
(17). Taylor (15) shows that the diffusion coefficient can be
calculated by integrating the autocorrelation function, Rii ðτÞ, of
where hi denotes ensemble averaging performed over trajectories of the same species. The asymptotic value of Dii ðτÞ, as
τ→∞, yields the Fickian diffusion coefficient.
There are two concerns about the applicability of the above
theory to determine the rate of dispersion for motile cells: (i)
Although it has been applied to study dispersion of passive
particles in various flow conditions, for motile microorganisms,
one might be concerned about bias caused by, e.g., chemotaxis,
phototaxis, or gyrotaxis. Following the treatment of atmospheric
diffusion of heavy particles by Csanady (16) or of fuel droplets by
Gopalan et al. (19), we remove the drift velocity from each
Lagrangian track by subtracting its mean value. Thus, the autocorrelation function is based on the fluctuation of instantaneous
velocity. (ii) The underlining assumptions for the theory to be
valid are that the diffusion is a random Gaussian process and
that the suspension should have a low void fraction (<0.02%);
i.e., the dynamical system does not possess long-term memory
and does not involve particle–particle interactions. Our data
show that the NND statistics for organisms of the same species
have a random distribution [see Sheng et al. (ref. 20) for 2064
data], suggesting that interaction among organisms of the same
species does affect their arrangement in space. Further, the
cross-correlation between two different velocity components
decays at least one order of magnitude faster then the autocorrelation function, suggesting the long-term dispersion is not
affected significantly by the complex swimming. Table 1 presents
all three components of the asymptotic diffusion coefficient.
1. Deeds JR, Terlizzi DE, Adolf JE, Stoecker DK, Place AR (2002) Toxic activity from
cultures of Karlodinium micrum (=Gyrodinium galatheanum) (Dinophyceae) - a
dinoflagellate associated with fish mortalities in an estuarine aquaculture facility.
Harmful Algae 1:169–189.
2. Bachvaroff TR, Adolf JE, Place AR (2009) Strain variation in Karlodinium veneficum
(Dinophyceae): Toxin profiles, pigments, and growth characteristics. J Phycol 45:
137–153.
3. Kempton JW, Lewitus AJ, Deeds JR, Law JM, Place AR (2002) Toxicity of Karlodinium
micrum (Dinophyceae) associated with a fish kill in a South Carolina brackish
retention pond. Harmful Algae 1:233–241.
4. Van Wagoner RM, et al. (2008) Isolation and characterization of karlotoxin 1, a new
amphipathic toxin from Karlodinium veneficum. Tetrahedron Lett 49:6457–6461.
5. Peng J, Place AR, Yoshida W, Anklin C, Hamann MT (2009) Structure and absolute
configuration of karlotoxin. An ichthyotoxin with global distribution from the marine
dinoflagellate Karlodinium veneficum. JACS in press.
6. Deeds JR, Place AR (2006) Sterol specific membrane interactions with the toxins from
Karlodinium micrum (Dinophyceae) - a strategy for self-protection. Afr J Mar Sci 28:
421–425.
7. Li A, Stoecker DK, Coats DW (2000a) Mixotrophy in Gyrodinium galatheanum
(Dinophyceae): grazing responses to light intensity and inorganic nutrients. J Phycol
36:33–45.
8. Li A, Stoecker DK, Coats DW (2000b) Spatial and temporal aspects of Gyrodinium
galatheanum in Chesapeake Bay: distribution and mixotrophy. J Plank Res 22:
2105–2124.
9. Adolf JE, Bachvaroff TR, Place AR (2008) Can cryptophyte abundance trigger toxic
Karlodinium veneficum blooms in eutrophic estuaries? Harmful Algae 8:119–128.
10. Bachvaroff TR, Adolf JE, Squier AH, Harvey HR, Place AR (2008) Characterization and
quantification of karlotoxins by liquid chromatography-mass spectrometry. Harmful
Algae 7:473–484.
11. Berges JA, Franklin DJ, Harrison PJ (2001) Evolution of an artificial seawater medium:
Improvements in enriched seawater, artificial water over the last two decades. J
Phycol 37:1138–1145.
12. Davison AC, Hinkley D (2006) Bootstrap Methods and Their Applications (MIT Press,
Cambridge, MA).
13. Keller EF, Segel LA (1971) Model for chemotaxis. J Theor Biol 30:225–234.
14. Tennekes H, Lumley JL (1972) A First Course in Turbulence (MIT Press, Cambridge, MA).
15. Taylor GI (1921) Diffusion by continuous movements. Proc Lond Math Soc 2:196–212.
16. Csanady GT (1963) Turbulent diffusion of heavy particle in the atmosphere. J Atmos
Sci 20:201–208.
17. Cushman JH, Moroni M (2001) Statistical mechanics with three-dimensional particle
tracking velocimetry experiments in the study of anomalous dispersion. I. Theory.
Phys Fluids 13:75–80.
18. Snyder WH, Lumley JL (1971) Some measurement of fluid-particle motion in an
isotropic turbulent field. J Fluid Mech 48:41–71.
19. Gopalan B, Malkiel E, Katz J (2008) Experimental investigation of turbulent diffusion of
slightly buoyant droplets in locally isotropic turbulence. Phys Fluids 20:095102–095115.
20. Sheng J, et al. (2007) Digital holographic microscopy reveals prey-induced changes in
swimming behavior of predatory dinoflagellates. Proc Natl Acad Sci USA 104:17512–17517.
S5: Swimming-Induced Dispersion Using Lagrangian Trajectories.
Conventional transport of microorganisms at population scales
has been traditionally modeled as a Fickian diffusion process; i.e.,
the flux is proportional to the concentration gradient. The
resulting diffusion equation is
Sheng et al. www.pnas.org/cgi/content/short/0912254107
2 of 8
Fig. S1.
Structures of the karlotoxins and related compounds. 1, KmTx-1; 2, KmTx-2; and 3, amphidinol. (a) Amphidinol 1. (b) Desulfoamphidinol 1.
Fig. S2. Effects of purified KmTX-1-1 on cell size and percentage of inhibition (PS II), which indicates reduction in photosynthetic efficiency of the cryptophyte,
Storeatula major.
Sheng et al. www.pnas.org/cgi/content/short/0912254107
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Fig. S3. Mixtrophically feeding K. veneficum CCMP 2778 grows faster and has lower karlotoxin (KmTx-2 for this strain) cell quotas. The overall average growth
rates for each growth cycle are presented above each curve. The dotted line connects the average toxin cell quota at each sampling point.
Fig. S4. Sample trajectories of various K. veneficum strains before mixing with S. major: (a) 1974; (b) MD5; (c) BM1 in a right-hand helix; (d) BM1 in a complete
left-hand helix. Trajectories are colored coded by velocity magnitude. (Scale bar: 40 μm.)
Sheng et al. www.pnas.org/cgi/content/short/0912254107
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Fig. S5. Probability density function of NND (solid line, bar graph) superimposed with those obtained for random distributions (dashed-dotted line) at the
corresponding cell concentrations. Solid line: Cross-NND between the group of toxic K. veneficum strain 1974 swimming at the average speed of 160 μm/s and
cryptophyte prey S. major. Bar graph: Cross-NND between the group of motile 1974 swimming at low velocity and prey S. major. Clustering is observed for both
groups, but much more pronounced in the latter group.
Sheng et al. www.pnas.org/cgi/content/short/0912254107
5 of 8
After introducing S. major
Alone
-6
2
MD5
Dzz
10 m /s
2.5
-6
2
Five hours after introducing S. major
10-6 m2/s
10 m /s
MD5
1974
10 m /s
BM1
10 m /s
2064
10 m /s
MD5
Dispersion Coef
2
1.5
1
Dxx
0.5
Dyy
0
1.8
0
-6
1.6
10 m /s
2
1974
10-6 m2/s
10-6 m2/s
BM1
10-6 m2/s
5
10
-6
2
-6
2
-6
2
15
t (sec)
20
25
Dispersion Coef
1.4
1.2
1
0.8
0.6
0.4
0.2
0
2
t (sec)
BM1
1.8
Dispersion Coef
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
2
10-6 m2/s
2064
1.8
10-6 m2/s
2064
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
5
10
15
t (sec)
20
25 0
5
10
15
t (sec)
20
25 0
5
10
15
t (sec)
20
25
Fig. S6. Dispersion coefficients of several strains of K. veneficum when it is alone (Left), shortly after it is mixed with prey (Center), and 5 h later (Right). Each
row shows a different strain, as indicated. Green, Dzz(t); red, Dxx(t); and blue, Dyy(t), with x, y, and z denoting the two horizontal and vertical directions,
respectively.
Sheng et al. www.pnas.org/cgi/content/short/0912254107
6 of 8
Five hour later
After introducing predator
Alone
0.8
10-6 m2/s
-6
2
10-6 m2/s
with MD5
10 m /s
with MD5
Dispersion Coef
0.6
0.4
0.2
0
0
5
10
15
20
25 0
5
-6
10
15
2
20
25
0
5
10
15
20
25
with 1974
10 m /s
Dispersion Coef
0.6
0.4
0.2
0
0.80
5
-6
10
15
2
20
25
with BM1
10 m /s
-6
2
with BM1
-6
2
with 2064
10 m /s
Dispersion Coef
0.6
0.4
0.2
0
0.8 0
5
10
15
10-6 m2/s
20
25
with 2064
10 m /s
Dispersion Coef
0.6
0.4
0.2
0
0
5
10
15
20
25 0
5
10
15
20
25
Fig. S7. Dispersion coefficients of prey (S. major) before mixing with predator, shortly after mixing, and 5 h later. Predator strains to which the prey is exposed
are indicated in each row. Line styles are the same as in Fig. S4.
Sheng et al. www.pnas.org/cgi/content/short/0912254107
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Table S1. Summary of S. major swimming characteristics and percentage of immotile cells when it is exposed to K. veneficum strains
and exogenous toxin solution
S. major
(immotile)
S. major (motile)
Strain
S. major
MD5 + S. major (h0)
MD5 + S. major (h5)
1974 + S. major (h0)
BM1 + S. major (h0)
BM1 + S. major (h5)
2064 + S. major (h0)
2064 + S. major (h5)
Methanol (h5)
KmTx-1, 2.5 ng·mL−1 (h5)
KmTx-2, 2.8 mL−1 (h5)
V ± σV, μm/s
|R| ± σR, μm
ω ± σω, rad/s
% immotile cells
86.4 ± 47.0 [86.2, 86.6]
85.2 ± 46.1 [85.1, 85.4]
86.8 ± 40.1 [86.7, 87]
42.7 ± 37.7 [42.4, 42.96]
65.1 ± 41.9 [64.9, 65.3]
69.8 ± 44.6 [69.5, 70.1]
81.7 ± 44.4 [81.5, 82.1]
63.2 ± 41.4 [62.9, 63.5]
78.85 ± 29.74 [78.1, 78.9]
60.77 ± 36.72 [60.5, 61.1]
70.3 ± 28.44 [70.31, 70.34]
5.8 ± 6.1 [5.84, 5.89]
5.1 ± 5.9 [5.1, 5.12]
6.1 ± 4.8 [6.11, 6.13]
2.9 ± 4.3 [2.8, 2.9]
4.1 ± 4.8 [4.1, 4.13]
5.1 ± 6.0 [5.0, 5.1]
4.7 ± 5.2 [4.70, 4.77]
4.2 ± 5.6 [4.21, 4.28]
3.58 ± 3.63 [3.55, 3.61]
3.09 ± 3.03 [3.06, 3.10]
5.17 ± 4.74 [5.16, 5.18]
7.3 ± 4.0 [7.33, 7.36]
7.2 ± 3.8 [7.21, 7.25]
7.8 ± 2.5 [7.81, 7.83]
8.1 ± 4.1 [8.10, 8.16]
6.9 ± 3.2 [6.90, 6.94]
6.7 ± 3.3 [6.71, 6.76]
6.9 ± 3.5 [6.84, 6.89]
6.4 ± 3.0 [6.41, 6.45]
6.51 ± 2.92 [6.47, 6.58]
7.92 ± 3.56 [7.92, 7.95]
5.7 ± 4.3 [5.71, 5.78]
31.1
28.1
29.7
52.9
27.8
53.0
37.0
60.1
32.6
89.1
57.8
Clearly shown in Table 1, S. major slows down when exposed to exogenous karlotoxins; however, the levels of immobilization are consistent with the
toxicity of ecologically relevant toxin concentration. Statistics are provided as mean ± SD. The numbers presented in brackets below each value show the 95%
CI based on bootstrap tests of the mean values. Immotile cells are those having trajectories with vertical linear motion not exceeding a velocity of ∼5–6 μm/s.
Movie S1. Successful predation. K. veneficum (strain 2282) capturing and ingesting S. major.
Movie S1
Sheng et al. www.pnas.org/cgi/content/short/0912254107
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