Why Sequence Hypersaline Microbial Mats?

Hypersaline microbial mats are complex, integrated ecosystems that have become models for studies of chemical and energetic factors that support photosynthesis-driven communities. Although the overall energy influx is photosynthetic, metabolism and turnover of photosynthetic organisms creates a rich and complex chemical ecosystem. Hypersaline mats popularly are considered simple communities. However, recent studies of the extensive (~150 sq. km) hypersaline mats at Guerrero Negro, Baja California, one of the best studied of such ecosystems, have revealed that in fact those mats are enormously complex and highly stratified with respect to both chemical and microbial diversity. To interpret the distributions of phylogenetic kinds of organisms (phylotypes) and metabolisms observed in any environmental survey, it is critical to understand the local (microscopic) chemical conditions. Thus, the Guerrero Negro hypersaline mats offer a system for understanding the interdependence of microbial community composition and biogeochemistry.

The Guerrero Negro mats offer a spectacularly fruitful ground for exploration of phylogenetic and metabolic diversity. Bacterial diversity is driven by chemical gradients that establish different metabolic niches, not by geographic location. Correlation of the phylogenetic and physiological makeup of the mat community with the detailed chemistry will provide the most comprehensive view ever obtained of the workings of a microbial ecosystem. The phylogenetic information obtained will allow for direct comparison of microbial diversity with geochemistry. Analysis of rDNA clones will provide a substantial increase in the numbers and detail of microbial phylogeny, which will be applicable to a very large community of microbiologists. Additionally, this study will be the first trial of comparative metagenomics with unassembled sequence data at a sub-habitat level. This approach holds great promise for providing detailed correlations of function, phylogeny, and geochemistry in a complex community. The project is a model of what microbial biologists need to do to begin to understand the myriad and interwoven microbial ecosystems that drive the biosphere.

CSP project participants: Norman R. Pace (proposer, Univ. of Colorado, Boulder) and Phil Hugenholtz (JGI).