Award: OCE-1357238

At the Guaymas Basin in the Gulf of California, hot fluids rich in petroleum, sulfide, methane and other gases emerge at the seafloor and sustain microorganisms that utilize these chemicals as a food and energy source. These microorgansisms are important since they capture the greenhouse gas methane and degrade petroleum to carbon dioxide, which can be taken up by living organisms; in this way, fossil carbon returns naturally into the biosphere. By genomic analysis of the naturally occurring microbes in Guaymas Basin sediments, we have discovered many new types of microorganisms (generally members of the domain archaea) living without oxygen in these sediments; these archaea can turn methane and other gases that originate deeply below the seafloor into carbon dioxide, and thus make it possible for these fossil carbon compounds to re-enter the biosphere. We have also continued previous work to understand how microorganisms that assimilate carbon dioxide into biomass obtain energy by respiration. These organisms (members of the family Beggiatoaceae) form large microbial mats on the seafloor, right on top of the sediments that contain the gas-processing archaea. It turned out that Beggiatoaceae can respire without oxygen, instead they can use nitrate and nitrite, and also some sulfur compounds (tetrathionate) that occur naturally at the seafloor interface. The Beggiatoaceae are in tun consumed by small worms and crabs, and enter the marine food chain. To summarize the ecology of Guaymas Basin, the archaea that utilize geothermal gas and other hydrocarbons and oxidize it to carbon dioxide, and the microbial mats that turn carbon dioxide into biomass, work together to recycle fossil carbon and to re-insert it into the marine foodchain. In addition, many archaea in Guaymas Basin, regardless of their hydrocarbon-processing capabilities, turned out to be extremely interesting from an evolutionary viewpoint. A major subgroup of archaea, the Asgardarchaea, can produce structural proteins and intracellular signal compounds that are otherwise typical of eukaryotic cells; these archaea are therefore considered descendants of the ancentral archaea that gave rise to the eukaryotic domain of life billions of years ago. Numerous genomes of different Asgardarchaea were found in Guaymas Basin hydrothermal sediments; this result was entirely unexpected and will certainly inspire future research directions. Not to forget, one of these Asgardarchaea, the newly discovered Helarchaea that were found so far only in Guaymas Basin, has the genes to process hydrocarbon gases. Last Modified: 07/22/2019 Submitted by: Andreas P Teske