Microbial food webs
PICOPLANKTON
Definition of size fractions
Short history of picoplankton
Before 1900 – largely unknown
Early 1900 – growing awareness
- food for oyster larvae, cell
counts of µ-algae
- culturing of marine bacteria
From ca 1950 – Serial dilution cultures of µ-algae
several descriptions of µ-algae
From ca 1970 – Electron microscopy – species identification
-- Fluorescence microscopy – cell numbers
-- HPLC (high performance - pigments
liquid chromatography)
-- Flow cytometry – distribution, cell numbers
From ca 1990 – Molecular methods
- FISH probes(fluorescent in situ
hybridisation)
- Clone libraries
- DGGE (denaturing gel
electrophoresis
From ca 2000 – sequencing of whole genoms
-- genomics – functional genes
Photosynthetic picoplankton
Fluorescence microscopy, blue light – autoflourescence
Yellow cells – cyanobacteria
Red cells - eukaryotes
Heterotrophic picoplankton
Miller 2004
fluorescens microscopy of heterotrophic bacteria
stained with DAPI, ultra violet light
In most studies picoplankton
is usually defined as cells
passing trough a 3 µm filter
(A-K) Photosynthetic and
eukaryotic picoplankton
(A-C) Micromonas pusilla
(F-G) prasinophyte
(D-E) prasinophyte
Imantonia rotunda
Phaeocystis pouchetii
Scanning electron microscopy; (C)
Transmission electron microscopy
of thin sections (A, B, E, K)
and whole-mounts (F, H, J)
Indian Ocean
Transect from
Africa to Australia
DCM – deep chlorphyll max
Picoprokaryote – Prochlorococcus, Synecochoccus
Picoeukaryotes < 3 µm, large cells > 3µm
Not et al 2008
surface
Indian Ocean - transect
Station 1 – African coast
Station 23 – Cook Island
DCM
From clone libraries
Not et al 2008
< 5 µm fraction
dominates
chlorphyll max at
all stations
Masquelier & Vaulot 2008
Prasinophytes and haptophytes are
important components of the
picoplankton of Norwegian waters
(A) Variations in Chl a
biomass as measured by
HPLC (total <200-µm
and fraction <3-µm) at
the ASTAN station.
(B) Contributions of the
division Chlorophyta and
of the orders
Mamiellales,
Prasinococcales, and
Pseudoscourfieldiales to
the picoplankton fraction
(<3-µm diameter)
according to the
CHEMTAX algorithm
applied to HPLC data.
Not et al. 2004
English Channel
(A) Picoeukaryotic photosynthetic cells
detected by flow cytometry counts (Flow
Cytometry); picoeukaryotic cells targeted
by the mix of the general probes
EUK1209R, CHLO01, and NCHLO01
(EUK1209R+CHLO01+NCHLO01); and
cells belonging to the division
Chlorophyta detected by the probe
CHLO02 (CHLO02).
(B) Cells targeted by the probe CHLO02 and
cells detected by the probes specific for
the clades PRAS01, PRAS03, PRAS04,
PRAS05, and PRAS06.
(C) Cells targeted by the probe specific for
Mamiellales (PRAS04) and cells detected
by the probes (MICRO01, BATHY01, and
OSTREO01) specific for the species and
genera.
Not et al. 2004
Abundances (number of cells ml–1) of photosynthetic picoplankton off Roscoff (western
English Channel) between July 2000 and September 2001. The average percentages over
the time series of the different groups are represented in pie charts.
Picoplankton important fraction of the phytoplankton
Temperate waters; often dominant in numbers,
sometimes in biomass
Tropical-oligotrophic waters
numbers and biomass often dominated by picoplankton e.g. in deep chlorophyll max (DCM)
Pico-eukaryotes dominates the picoplankton fraction in
Arctic waters
• Cyanobacteria;
• Important in all oceans except the polar
seas.
• Synechococcus; temperate and tropical
• Prochlorococcus; sub tropical and tropical
Micromonas pusilla
Scanning electron microscopy
Light microscopy
Micromonas pusilla (Butcher) Manton
& Parke 1960
1.5-2.5 µm
Pico sized prasinophyte common in all oceans