Organic sulfur metabolisms in Eastern Lau Spreading Center hydrothermal vents

Abstract

Sulfur is a central element in deep-sea hydrothermal vent systems, and many thermophiles isolated from these environments have sulfur-based metabolisms. However, it is not known what role organic sulfur compounds might play in deep-sea vent microbial ecology. Geochemical models are used to predict fluid compositions resulting from mixing of end-member hydrothermal fluids from the Eastern Lau Spreading Center (ELSC) with bottom seawater. These fluid compositions combined with estimated activities of dimethylsulfide and methanethiol are used to evaluate the potential for organic sulfur-based metabolisms under hydrothermal conditions. The transition temperature at which aerobic metabolisms outcompete anaerobic metabolisms varies (from ~75˚C to >200˚C) with end-member vent fluid chemistry. Aerobic respiration has the highest energy yields (> 575 kJ/mol C) at lower temperatures, while anaerobic metabolisms such as sulfate reduction and methanogenesis are favored at higher temperatures (~100˚C to 200˚C). Enrichment cultures targeting organic sulfur-based metabolisms inoculated with ELSC chimney slurries were successfully established. The cultures contained species of Thermococcales, ε-Proteobacteria, Thermales, and Aquificales as well as 2 novel bacterial sequences. These data suggest that organic sulfur-based metabolisms may be viable within deep-sea hydrothermal vents.