Extremophilic Microbes from Serpentinite Mud Volcanoes

The study of environmental and biological analogs on Earth is central to astrobiology and the search for extraterrestrial life. The deep sea is an analog for liquid oceans found on icy moons within our solar system. The oceans within Europa and Titan may extend hundreds of kilometers below the surface, reaching high pressures; the pH of Enceladus’ ocean is predicted as high as 12, presumably due to serpentinization. The Mariana forearc serpentinite mud volcanoes are strong terrestrial analogs for these extraterrestrial environments. We are investigating the culturable piezophilic (high pressure adapted) and alkaliphilic (high pH adapted) microbes within this ecosystem using sediments collected during IODP Expedition 366. Three seamounts were drilled – Yinazao, Fantangisña, and Asùt Tesoru – and sediments from as deep as 139 meters were recovered. These seamounts lay 1.2-3.6 kilometers below sea level, where hydrostatic pressures are great enough to influence microbial activity. Microbes may also follow conduit fluid flow from far below the seafloor, where pressures are even greater. The porewaters of these sediments are high in pH (up to 12.5) and laden with H₂, CH₄, and small molecule organics such as formate and acetate. Isolates belonging to the genera Halomonas, Marinobacter, and Demiquina were obtained by plating the sediments on rich media of pH 7.4 and 10.5; their adaptation to extreme conditions is being assessed. 180 high-pressure, high-pH microcosms were also established, targeting a range of metabolisms. Preliminary 16S tag sequencing of cDNA from successfully enriched microcosms reveals unexpected diversity. These sequences span the phyla Proteobacteria, Cyanobacteria, Planctomycetes, Bacteroidetes, Acidobacteria, and Firmicutes. Future work includes targeted isolation and characterization of microbes from these sediments and microcosms. This work will assist in our investigation of microbial adaptation to extreme environments – on Earth and beyond.