Bacterioplankton is mainly responsible for the recycling of nutrients and the decomposition of organic matter in freshwater ecosytems (Fisher et al., 2000).
Relative importance of nutrients and mortality factors on prokaryotic community composition in two lakes of different trophic status Ludwig JARDILLIER (FEMS Microb Ecol, in revision)
Laboratory of Protist Biology UMR CNRS 6023 Clermont-Ferrand, FRANCE
The bacterioplankton ! Bacterioplankton is mainly responsible for the recycling of nutrients and the decomposition of organic matter in freshwater ecosytems (Fisher et al., 2000) ! Resources, predation & viral lysis are the main factors controlling bacterial dynamics ! Bottom-up and top-down controls seems to be more important in oligotrophic and eutrophic systems, respectively (Sanders et al., 1992).
The Prokaryotic Community Composition (PCC) ! Some studies have indicated variations in the Bacterial Community Composition (BCC) with time ! Many studies have shown that predation by protists and zooplankton can bring to changes in BCC ! Some seasonal studies or experiments have shown that resources influence BCC ! Current knowledge of the main factors controlling PCC is on the whole not well advanced
Questions ! What is the impact of predation, viruses and resources on prokaryotic communities (Eubacteria and Archaea)? ! What is the relative importance of each of these two variables? ! Does this relative importance depend on trophic status?
Study sites SEP RESERVOIR
AYDAT LAKE
OLIGO-MESOTROPHIC
EUTROPHIC
Altitude : 500 m
825 m Max depth :
37 m
15 m area :
33 ha
60 ha
Microcosms experiments < 1.2 µm
< 10 µm
Lake level = NP(-) Enrichment = NP(+) t=0h
t = 24 h
t = 48 h
CONCOMITANT CONTROL of: - predation by differential filtration -and resources level by enrichment
UNF
Fluorescent in situ hybridization (FISH) DAPI-stained cells
FISH
Groups targeted and oligonucleotidic probes used : - Eubacteria : EUB338 - alpha-proteobacteria : ALF1b - beta-proteobacteria : BET42a - Cytophaga-Flavobacterium : CF319a - Archaea : ARCH915
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