title: Trophic interactions between viruses, bacteria and nanoflagellates under various nutrient conditions and simulated climate change.
abstract: Population dynamics in the microbial food web are influenced by resource availability and predator/parasitism activities. Climatic changes, such as an increase in temperature and/or UV radiation, can also modify ecological systems in many ways. A series of enclosure experiments was conducted using natural microbial communities from a Mediterranean lagoon to assess the response of microbial communities to top-down control [grazing by heterotrophic nanoflagellates (HNF), viral lysis] and bottom-up control (nutrients) under various simulated climatic conditions (temperature and UV-B radiations). Different biological assemblages were obtained by separating bacteria and viruses from HNF by size fractionation which were then incubated in whirl-Pak bags exposed to an increase of 3°C and 20% UV-B above the control conditions for 96 h. The assemblages were also provided with an inorganic and organic nutrient supply. The data show (i) a clear nutrient limitation of bacterial growth under all simulated climatic conditions in the absence of HNF, (ii) a great impact of HNF grazing on bacteria irrespective of the nutrient conditions and the simulated climatic conditions, (iii) a significant decrease in burst size (BS) (number of intracellular lytic viruses per bacterium) and a significant increase of VBR (virus to bacterium ratio) in the presence of HNF, and (iv) a much larger temperature effect than UV-B radiation effect on the bacterial dynamics. These results show that top-down factors, essentially HNF grazing, control the dynamics of the lagoon bacterioplankton assemblage and that short-term simulated climate changes are only a secondary effect controlling microbial processes.
authors: UMR 5119, ECOSYM, Ecologie des systèmes marins côtiers, UM2, CNRS, IRD, Ifremer, UM1. Université Montpellier 2, Place Eugène Bataillon, Case 093, 34095 Montpellier cedex 5, France. marc.bouvy@ird.fr
authors: M
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authors: Bouvy
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authors: Bettarel
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authors: Bouvier
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authors: Domaizon
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authors: Jacquet
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authors: Le Floc'h
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authors: Montanié
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authors: Mostajir
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authors: Sime-Ngando
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authors: Torréton
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authors: Vidussi
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authors: Bouvier