In summer, the differences in the structure induced by the size fractionation were the strongest, and sample discrimination was clearly linked to the fractionation (1.6 vs. 5 μm). Similar patterns were obtained for Lake Bourget in summer. Finally, treatment VFA was highly divergent from GSK2245840 V and VF (between 42% and 58% of similarity) during the early spring experiment for Lake Bourget. Figure 5 Cluster analysis of DGGE profiles based on band position

and intensity. Scale bars indicated the Bray-Curtis similarity index in Lake Annecy (A) and Lake Bourget (B). V0 and VFinal, treatment Viruses+Bacteria at the beginning and the end of experiments; VF0 and VFfinal, treatment Viruses+Bacteria+Flagellates at the beginning and the end of experiments, VFAfinal, treatment Viruses+Bacteria+Flagellates+Autotrophs at the end of experiments. Discussion Experimental buy Rabusertib approach In order

to study the influence of both predation pressure and the autotrophic activity on bacterial community of Lakes Annecy and Bourget, we carried out a fractioning approach and performed incubation in either darkness or ambient light. The originality and strength of this study comes from the fact that such experiments were conducted (i) in two ecosystems with either oligotrophic or Y-27632 mouse mesotrophic status and (ii) at two distinct periods of the year (i.e. early-spring and summer) where microbial planktonic dynamics and composition are likely to display clear differences [8, 24, 25]. Although the use of microcosms may introduce some bias into the development of microbial communities compared with those occurring naturally in the field (due to confinement and handling effects), these experimental tools are still very useful for investigating how processes such as mortality Ceramide glucosyltransferase factors induce temporal variation in bacterial dynamics, structure and activity [26]. Incubation time (4 days) coupled

with the volume of microcosms (2.5 L) considered in this study have previously been used successfully in other experimental studies [18, 22]. We assumed that our design was thus realistic enough compared to the generation time of microorganisms and aimed to obtain significant changes in bacterial and viral activity [27]. A comparison of virus and flagellate abundances at the onset of the experiments with in situ conditions and among treatments with different viral and flagellate effects was successful. However, the experimental protocol resulted in a reduction of HNF at the start of the experiment and we thus might have underestimated their influence. Clear effects of HNF were observed at the end of the experiment, when flagellate abundance was about twice as high as in situ (Tables 1 and 2). Grazing effect on viral activity According to the model of Miki and Yamamura [28], grazers should reduce the role of the viral loop.