Jake Dittrich1, Kimberly Halsey2
BioResource Research 1, Department of Microbiology2
Oregon State University, Corvallis, Oregon
Overview
 Introduction and Background
 Materials and Methods
 Results
 Discussion
 Conclusions
Global Carbon Cycle
•The world’s oceans are a major regulator of atmospheric carbon levels, sequestering
up to a third of the anthropogenically produced carbon.
The Marine Biological Pump
Idealized schematic of the marine biological pump.
Marine Net Primary Production
 Net Primary Production (NPP)
 Photosynthesis
 Accumulation of biomass


Light Availability
Nutrient Availability

Nitrogen
Nitrogen Limitation
 Much of the worlds oceans are nitrogen limited.
 Nitrogen limitation is predicted to increase.
 Decreasing mixed layer depth
Nutrient cycling
 Seasonal phytoplankton blooms
 Biological pump

Video credit NASA.gov/SeaWiFS
Nitrogen limitation
30
10
0
Nitrate
 Nitrogen limitation effects
NPP of cyanobacteria.
 Carbon cycling in the worlds
oceans.
 Oceanic models of primary
productivity.
(mmol kg-1)
20
The Question
 No reasonably effective methods for measuring Net
Primary Production (NPP) in the worlds oceans directly
 NPP = growth rate times cellular carbon.
 Chlorophyll a concentration (Chl) measured via remote
satellite sensing.
 Chl then related to NPP through the Chl-specific carbon
fixation rate (Pb)
Carbon/Chl/Unit Time
12
10
6
Chl-specific
carbon fixation
NPP* Predicted
4
NPP* Alternative
8
2
0
0
0.2
0.4
0.6
0.8
Specific Growth rate (d-1)
1
Idealized schematic of the potential relationships between Pb and NPP*.
Experimental Summary
 NPP* independent or dependent on nitrogen limited
growth for Synechococcus WH8102.
 My research investigated the relationships between
nitrogen limited specific growth rate, Chl-specific carbon
fixation rates, and NPP*.
Why Synechococcus WH8102?
 Motile
 Unknown
 No physical appendage
 10-10 M nitrogen concentration
 Ubiquitous
 Second only to Prochlorococcus in abundance

Synechococcus WH8102 cells are larger and grow faster
 Significant contributor to global marine primary production
 An Oligotrophic organism
 Nitrogen uptake
A Little Bit of Scale Reference……
Synechococcus
WH8102
Experimental Design
 7 Chemostats
 3 growth rates
0.2 day-1
0.5 day-1
1.0 day-1
 Natural seawater
 Nitrogen limited
 7 Generations
Schematic of experimental setup for steady-state
N-limited growth of Synechococcus WH8102.
Chemostats
Experimental Measurements
 Short term (20 min) 14 C uptake
data.
 Pb
 Cellular Carbon and Nitrogen
 Elemental Analyzer
 Chlorophyll Concentration
 Spectrometry
Steady-state N-limited
cultures of Synechococcus
WH8102
 Statistical Analysis
 Linear regression, ANOVA
Chl/ cell (femtograms/cell)
Chlorophyll a per cell for Synechococcus WH8102
40
35
30
25
20
15
10
5
0
0
0.2
0.4
0.6
0.8
Specific growth rate (d-1)
1
1.2
Comparison of chlorophyll:carbon for three marine phytoplankton
35
30
Chl C-1 x 103 (µg µg-1)
25
20
Synechococcus
WH8102
Dunaliella
tertiolecta
Thalassiosira
weissflogiii
15
10
5
0
0
0.5
1
Specific Growth Rate (d-1)
1.5
Data for D. tertiolecta and T. weissflogi from Halsey et al. (2010); Halsey et al. (2013).
Chl-specific production (µmol C
(mg Chl*h)-1
Chlorophyll specific net primary production and carbon fixation for
Synechococcus WH8102
350
300
250
200
150
100
NPP*
50
Pb
0
0
0.2
0.4
0.6
0.8
Specific Growth Rate (d-1)
1
C fixation (µmol C (mg Chl x h)-1
Photosynthesis irradiance curves for chl-specific 14C uptake data
350
300
250
200
150
100
0.2
50
0.5
1.0
0
0
500
1000
1500
Light intensity (µmol quanta m-2 x sec-1)
2000
Discussion
 Cyclic electron flow at Photosystem I

Additional energy production
 Alternative forms of reduced nitrogen
 Unique form of motility
 Sodium Motive force
 Synechococcus WH8102
Chl cell-1 increased with
increasing growth rate.
 Unique Motility
Chl/ cell
(femtograms/cell)
Discussion
40
30
20
10
0
0
 Nitrogen gradients
 10-10 molar
 Sodium motive force
 Na+/H+ antiporters
0.5
1
Specific growth rate (d-1)
Discussion
Chl C-1 (µg µg-1)
 Chl:C strongly dependent
on nitrogen limited
PSI/PSII ΔChl:C
growth rate for
T. weissflogii
0.5
7.2 (0.86)
D. tertiolecta
1
3.9 (0.74)
Synechococcus WH8102
Synechococcus sp.
2
2.2 (0.25)
 PSI/PSII ratios
30
 Previously studied
organisms
20
10
0
0
Data for D. tertiolecta and T. weissflogi from Halsey et al. (2010); Halsey
et al. (2013).
0.5
1
Specific Growth Rate (d-1)
1.5
Discussion
Fast growth rate 1.0d-1
Slow growth rate 0.2d-1
Conclusions
• Synechococcus WH8102 chl-specific net primary production is
dependent on nitrogen limited growth rate.
• Short term (20 min) chl-specific carbon fixation rates increased
with increasing growth rate.
• Pb cannot give estimates of NPP*
• Pb, NPP* and growth rate, suggest a different strategy for
carbon metabolism, pigment regulation, and photosynthetic
energy utilization in Synechococcus WH8102.
 Cyclic electron flow at Photosystem I
 Uptake of alternative forms of reduced nitrogen
 Unique motility
Acknowledgments
 Dr. Kimberly Halsey
 Dr. Michael Behrenfeld
 Dr. Peter Bottomley
 E.R. Jackman internship support program.
 Wanda Crannell
 Dr. Kate Field
 BioResources Research program
Cyclic Flow
PS II
N/S reduction,
direct utilization
PS I
Calvin
cycle
GAP
PTOX
Mehler
TCA, OPP
Storage
Net growth