AME 45:277-289 (2006)  -  doi:10.3354/ame045277

Effects of resource availability and bacterivory on leucine incorporation in different groups of freshwater bacterioplankton, assessed using microautoradiography

Karel Hornák1,2,*, Jan Jezbera1,2, Jirí Nedoma1, Josep M. Gasol3, Karel Simek1,2

1Biology Centre of the Academy of Sciences of the Czech Republic, Institute of Hydrobiology, Na Sádkách 7, 370 05 Ceské Budejovice, Czech Republic
2Faculty of Biological Sciences, University of South Bohemia, Branisovská 31, 370 05 Ceské Budejovice, Czech Republic
3Institute of Marine Sciences, CMIMA, Pg. Marítim de la Barceloneta 37–49, 08003 Barcelona, Spain

ABSTRACT: We examined changes in the phylogenetic structure and leucine incorporation of bacterioplankton assemblages exposed to variable levels of available resources and bacterivory in a freshwater reservoir. Fluorescence in situ hybridization (FISH) combined with microautoradiography was used to determine bacterial phylogenetic affiliations and the proportions of cells incorporating leucine. Grazing-free and grazing-enhanced treatments were incubated in both P-limited and P-rich areas of the reservoir using dialysis bags, and bottle treatments with and without P enrichment. β-Proteobacteria, mainly the R-BT065 cluster (subcluster of Rhodoferax sp. BAL47), became the dominant leucine-active bacteria in all treatments. Proportions of active cells belonging to R-BT065 phylotypes considerably increased under conditions of enhanced protistan grazing and phosphorus availability. In contrast, proportions of cells from the Sphingobacteria/Flavobacteria group usually decreased and exhibited very low rates of leucine uptake. γ-Proteobacteria was the least abundant but nevertheless a highly active part of the assemblage. Phosphorus addition supported incorporation of leucine by all bacterial groups. Although highly vulnerable to predation, only R-BT065 cells exhibited marked increases in both relative abundance within the bacterial community and in proportions of active cells. The phylogenetic composition and leucine-uptake of bacterioplankton was more markedly affected by resource availability than by grazing pressure, which only had a strong effect on the dynamics of R-BT065 bacteria within the P-limited area of the reservoir.

KEY WORDS: Reservoir bacteria · Resource availability · Bacterivory · Leucine incorporation · Bacterioplankton structure · Bacterioplankton function

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