How Divergent Is The Cuatro Cienegas Oasis? Genomic Studies Of Microbial Populations And Niche Differentiation

In this chapter, we describe some genomic studies that have been conducted in the CCB to describe the microdiversity of different microbial taxa. Firstly, we describe the genomic variation in the endemic species B. coahuilensis, for which we analyzed three strains, and the evolutionary mechanism that have shaped their genomes, in particular for their adaptations to a low phosphorus environment. Secondly, we describe population genomics of Proteobacteria such as Pseudomonas, Vibrio, Photobacterium, and Aeromonas, finding many genes related to bacterial interactions, such as type III and VI secretion systems, which led us to propose that these systems play an important role in interactions among bacterial communities. Many of these interaction genes have been classified previously as virulence factors. However, at CCB these genes were not found in a cassette configuration-such as an integron or a pathogenicity island-in any strain suggesting that they are very ancestral adaptive responses to keep both the cohesion within the community and the cheaters out of the community. Interestingly, even if B. coahuilensis presents many mobile elements, these elements are rare in the surveyed Proteobacteria, whose genomes present many CRISPS elements. The presence of CRISPR regions may also explain why there are few ISs or plasmids since it has been reported that CRISPR spacers can act as barriers against HGT.