Extreme environments Genome sequencing

For plants and animals, the relation between environmental limiting factors and patterns of abundance and diversity has been described since 1931 by Shelford’s law of tolerance. Microbial community studies to date suggest that this law can also be applied to the microbial world. However, whether and how trends observed in microbial communities can be extrapolated to specific microbial groups within them remains unclear. One such group is endospore-forming firmicutes (EFF) that, at spore state, can survive various adverse conditions. We hypothesize that the co-existence of multiple stressing environmental parameters, rather than a single limiting factor, favors the relative abundance of EFF and influences their diversity in extreme environments. In order to address this hypothesis we have collected 126 samples worldwide. 16S rRNA gene (total bacteria) and sporulation transcriptional factor spo0A gene (endospore-specific) copy numbers were estimated by quantitative PCR. Moreover, community composition based on 16S rRNA amplicon sequencing, was analysed in 9 samples representing environments with multiple, single or no stressing factors. The quantification showed that EFF are favored when a combination of stressing factors is present in the environment. At such sites, EFF are highly prevalent while in single factor and non-extreme environments they represent a small fraction of the microbial community. Diversity is also influenced by environmental parameters, depicting the high EFF metabolic diversity. These observations suggest that in extreme environments EFF behave as a ‘system within a system’ and are influenced by their environment in a different way than the whole bacterial community.