Seasonal and spatial variability of virio-, bacterio-, and picophytoplanktonic abundances in three peri-alpine lakes |
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Authors: | Sébastien Personnic Isabelle Domaizon Ursula Dorigo Lyria Berdjeb Stéphan Jacquet |
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Institution: | (1) INRA, UMR CARRTEL, Station d’Hydrobiologie Lacustre, 75 Avenue de Corzent, 74203 Thonon-les-Bains cedex, France;(2) Université de Savoie, UMR CARRTEL, 73376 Le Bourget du Lac cedex, France |
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Abstract: | Flow cytometry (FCM) was used to assess microbial community abundances and patterns in three natural, large and deep peri-alpine
hydrosystems, i.e., lakes Annecy (oligotrophic), Bourget, and Geneva (mesotrophic). Picocyanobacteria, small eukaryotic autotrophs,
heterotrophic prokaryotes, and viruses were studied in the 0–50 m surface layers to highlight the impact of both physical
and chemical parameters as well as possible biotic interactions on the functioning of microbial communities. Some specificities
were recorded according to the trophic status of each ecosystem such as the higher number of viruses and heterotrophic bacteria
in mesotrophic environments (i.e., Lakes Geneva and Bourget) or the higher abundance of picocyanobacteria in the oligotrophic
Lake Annecy. However, both seasonal (temperature) and spatial (depth) variations were comparatively more important than the
trophic status in driving the microbial communities’ abundances in these three lakes, as revealed by principal component analysis
(PCA). A strong viral termination of the heterotrophic bacterial blooms could be observed in autumn for each lake, in parallel
to the mixing of the upper lit layers. As virus to bacteria ratio (VBR) was indeed very high at this period with values varying
between 87 and 114, such important relationships between viruses and bacteria were likely. The magnitudes of seasonal variations
in VBR, with the highest values ever reported so far, were largely greater than the magnitude of theoretical variations due
to the trophic status, suggesting also a strong seasonality in virioplankton production associated to prokaryotic dynamics.
FCM analyses allowed discriminating several viral groups. Virus-Like Particles group 1 (VLP1) and group 2 (VLP2) were always
observed and significantly correlated to bacteria for the former and chlorophyll a and picocyanobacteria for the latter, suggesting that most of VLP1 and VLP2 could be bacteriophages and cyanophages, respectively.
On the basis of these results, new ways of investigation emerge concerning the study of relationships between specific picoplanktonic
groups; and overall these results provide new evidence of the necessity to consider further viruses for a better understanding
of lake plankton ecology.
Handling editor: Luigi Naselli-Flores |
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Keywords: | Viruses Bacteria Flow cytometry Lake Trophic status |
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