Photosynthetic microbial mats are complete microbial ecosystems that can construct laminated “miniature reefs” called stromatolites. Their fossilized equivalents are among the oldest most abundant evidence of early life. Dr. Des Marais and his colleagues have studied cyanobacterial mats in an arid coastal environment at the Exportadora de Sal, S.A. (ESSA) salt works, Guerrero Negro, Baja California Sur, Mexico. He will show how the mats' oxygenated zone reflects a dynamic balance between vigorous photosynthetic O2 production and O2 consumption by diverse sulfide-oxidizing and heterotrophic bacteria.
Anoxygenic phototrophs and sulfate-reducing bacteria are quantitatively important consumers of dissolved organic matter. He will show how several previously unknown rRNS gene sequences of bacteria and eukarya were identified, indicating that these mats can extend our understanding of the diversity and early evolution of benthic microbial communities. He continues to catalog the diversity of lipid biosignatures, whose fossil equivalents can record the diversity of ancient microbial ecosystems.