Marine microbial endoliths: biodiversity and function

Organisms that colonize the interior of rocks, shell hash and other skeletal fragments are known as endoliths. Coastal euendoliths are ideal model systems for microbial biogeographical studies, as coasts comprise the most abundant biome on the Earth that is stable, characterized by relatively low productivity and turnover rates. Euendoliths of marine environments especially along the intertidal and supratidal ranges of carbonate coasts are significant contributors to marine bioerosion, as documented by microscopic, but hardly any molecular studies. Endoliths expand our understanding about the ability of organisms to survive and even thrive in extreme conditions. They also raise new ideas regarding the possibility of extraterrestrial life and may alter our ideas about the origin of life on Earth.

Despite their environmental relevance, the mechanism that enables them to dissolve carbonates, even in waters supersaturated with respect to calcite and aragonite, has remained elusive. In our study we provide a comparative sequence analysis using MiSeq DNA and RNA pyrosequencing of the 16S rRNA gene combined with extensive microscopy of the endolithic community from different geographical regions, and different nutrient regimes.

Our forte is the use of molecular tools for the first time to carbonate penetrating microorganisms, where they naturally occur, an approach that will provide a direct information link between cell´s phylogenetic and metabolic markers. Our data provide information concerning16S rRNA RNA-seq vs. DNA pyrosequencing of heterotrophic bacteria and cyanobacteria in order to differentiate between active and dormant populations from coastal endoliths.

We applied for the first time single cell genomics (SCG) to endolithic organisms, matching phylogeny and metabolism in the uncultured cyanobacterial endoliths that dominate marine rocks and biochemical cycles.