community genomics of hot-springs at manikaran

Bdellovibrio bacteriovorus is a small bacterial predator that can invade, kill and assimilate its microbial prey. While B. bacteriovorus has been characterised from mesophilic environments (soil, marine and freshwater, etc.) these communities are not ammenable to metagenomic re-assembly of predatory and prey genotypes due to high taxonomic diversity and community eveness. Here we present the first metagenomic analysis of the microbial mats of an arsenic rich (140ppb) hot spring (surface temperature > 90 °C) in which the predator-prey genotypes were characterized. The microbial mats were enriched with Bdellovibrio and several Gram negative bacteria including Bordetella (16%), Enterobacter (6.8%), Burkoldria (4.8%), Acinitobacter (2.3%), and Yersinia (1%). A high quality (51 contigs, 25X coverage; 3.5Mbp) draft genome of B. bacteriovoras (strain ‘Meta’) was reasembled, which lacked two genes associatd with the established method of prey interaction and invaision, but still contained genes coding for the hydrolytic enzymes necessary for prey assimilation. Using predation experiments, a predatory B. bacteriovoras was identified that manifest a novel mode of predation via flagella supported side-on prey contact, without cellular invasion. Furthermore, a draft pangenome of the dominant host taxon, Enterobacter cloacae sub. sp, (4.8Mb), along with 2 of its viral genotypes (n=2; 42 and 50kb) was assembled. Viral predation and mainatnce of strain specificity in E. cloacae was confirmed by the presence of CRISPERs. These data were used to construct a theoretical model describing potential predator avoidance strategies, whereby the E. cloacae strains can move between anaerobic and aerobic niches by quroum sensing population size, which is modulated by a ‘kill the winner’ viral mechanism, and predation by the obligate aerobe, B. bacteriovoras.