UC San Diego

The Mariana Forearc is home to the only known active serpentinite seamounts on Earth. Serpentinization, a reaction that occurs when ultramafic rock is exposed to water, fuels these unique environments. These seamounts are home to microbial communities that have barely begun to be explored; only one species of bacteria had been isolated and described prior to this research. During International Ocean Discovery Program Expedition 366, sediment samples were obtained from three seamounts. In this research, I characterized ten strains of bacteria isolated at atmospheric pressure from samples obtained from two of the seamounts, Asùt Tesoru and Fantangisña. All of the isolates are closely related to previously cultured microbes and represent three genera: Halomonas, Demequina, and Marinobacter. These ten isolates were examined for pH tolerance, pressure tolerance, salinity requirement and tolerance, and temperature tolerance. The majority of these isolates were pressure-sensitive and alkaliphilic. The only previously characterized bacterium isolated from the seamounts, Marinobacter alkalphilus str ODP1200D-1.5, was obtained from the Japan Collection of Microorganisms, tested alongside the isolates, and sent for genome sequencing along with three of the isolates. Genomic analyses revealed several adaptations and metabolic capabilities that could contribute to survival in the seamounts, including Na+/H+ antiporters and acetate metabolism. The results of this research indicate that the characterized isolates could be active in situ, and therefore likely represent a portion of the active community at the seamounts. This thesis contributes to the knowledge of the microbial communities and adaptations required for life at serpentinite seamounts.