Diversity, Dynamics, and Distribution of and Like Organisms in Perialpine Lakes

Microbes drive a variety of ecosystem processes and services, but many of them remain largely unexplored because of a lack of knowledge on both the diversity and functionality of some potentially crucial microbiological compartments. This is the case with and within the group of bacterial predators collectively known as and like organisms (BALOs). Here, we report the abundance, distribution, and diversity of three families of these obligate predatory Gram-negative bacteria in three perialpine lakes (Lakes Annecy, Bourget, and Geneva). The study was conducted at different depths (near-surface versus 45 or 50 m) from August 2015 to January 2016. Using PCR-denaturing gradient gel electrophoresis (PCR-DGGE) and cloning-sequencing approaches, we show that the diversity of BALOs is relatively low and very specific to freshwaters or even the lakes themselves. While the family was represented mainly by a single species (), it could represent up to 7% of the total bacterial cell abundances. Comparatively, the abundances of the two other families ( and ) were significantly lower. In addition, the distributions in the water column were very different between the three groups, suggesting various life strategies/niches, as follows: dominated near the surface, while and were more abundant at greater depths. Statistical analyses revealed that BALOs seem mainly to be driven by depth and temperature. Finally, this original study was also the opportunity to design new quantitative PCR (qPCR) primers for quantification. This study highlights the abundance, distribution, and diversity of a poorly known microbial compartment in natural aquatic ecosystems, the and like organisms (BALOs). These obligate bacterial predators of other bacteria may have an important functional role. This study shows the relative quantitative importance of the three main families of this group, with the design of a new primer pair, and their diversity. While both the diversity and the abundances of these BALOs were globally low, it is noteworthy that the abundance of the could reach important values.