Microbes drive a variety of ecosystem processes and services but still many of them remain largely unexplored because of our lack of knowledge on both diversity and functionality of some potentially key microbiological compartments. This is typically the case with and within the group of bacterial predators collectively known as Bdellovibrio and like organisms (BALOs). Here we report for the first time the abundance, distribution and diversity of the three main families of these natural and obligatory predators of gram negative bacteria in three peri-alpine lakes (e.g. lakes Annecy, Bourget and Geneva) at different depths (surface vs. 45 or 50 m) and along a few months (from August 2015 to January 2016). We show that, using PCR-DGGE and cloning-sequencing approaches, the diversity appeared relatively low and very specific to fresh waters or even of the lakes themselves. While the Peredibacteraceae family was represented mainly by a single species (i.e. Peredibacter starii), it could constitute up to 7% of the total bacterial cell abundances. Comparati vel y, the abundances of the two other families (referred to as Bdellovibrionaceae and Bacteriovaracaceae) were significantly lower. More interestingly, the distribution in the water column was very different between the three groups suggesting various life strategies/niches for each of them:Peredibactereacea dominated near surface while the Bdellovibrionaceae and the Bacteriovaracaceae were more abundant at depth. All in all, our results suggest that these bacterial predators are likely to play a significant role in mortality, carbon fluxes and prokaryotic community structure in lakes.Date: September, 2017 Correspondence : S Jacquet, INRA, UMR CARRTEL, 75 avenue de Corzent, 4200 Thonon -les-Bains, France Email : stephan.jacquet@inra.fr 1 Current address : Laboratoire MAPIEM, Université de Toulon, CS 60584, 83041 Toulon cedex 9, France not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission.The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/194688 doi: bioRxiv preprint first posted online Sep. 27, 2017;
IntroductionOver the last few years, studies on western European large and deep peri-alpines lakes have shown that these ecosystems own a very diverse and dynamic auto-and heterotrophic prokaryotic community (Comte et al., 2006 ; Personnic et al., 2009 ;Debroas et al., 2009, Berdjeb et al., 2011Berdjeb et al., 2013 ;Domaizon et al., 2013 ;Ammini et al., 2014). These studies and others have also revealed that a large variety of both biotic and abiotic factors are likely to regulate these communities. Among these factors, inorganic nutrients, viruses, nanoflagellates and other heterotrophic grazers (including ciliates and/or metazooplankto n) have been identified as key players in the dynamics of abundance or community compositio n structure patterns (Domaizon et al., 2003 ; Comte et al., 2006 ;Personnic et al., 2009b ; Thomas et al., 2011 ; Berdjeb et al., 2011;Berdjeb et al., 2013;Perga ...