NOVEL EPSILONPROTEOBACTERIA FROM SAANICH INLET COUPLES BIOGEOCHEMICAL CYCLES IN ANOXIC MARINE ENVIRONMENTS

The oxygen content of the ocean is declining with currently unconstrained feedbacks on marine biogeochemical cycles and ocean ecology. Within low-oxygen environments (Oxygen Minimum Zones-OMZs), hydrogen sulfide can accumulate as a product of microbial sulfate respiration. The accumulation of hydrogen sulfide and depletion of oxygen in OMZs becomes toxic to higher order marine biota resulting in the formation of so-called marine dead zones. Such accumulations of sulfide, however, are often mitigated when marine microbes inhabiting OMZs couple sulfide oxidation to nitrate or oxygen reduction. Relative to the marine photoic zone, little is known of the ecology of OMZ microorganisms. Microbial fingerprinting using high throughput sequencing reveals conspicuous members of OMZ communities with metabolic potential to oxidize sulfide including the gammaproteobacteria SUP05, and the epsilonproteobacteria Sulfurimonas. Our work however suggests that these fingerprinting approaches may overlook key members of OMZ communities that play an important role in sulfide oxidation. We have applied cultivation and cultivation independent approaches to test for cryptic members of OMZ communities that might be involved in marine sulfide oxidation. Our enrichment cultures from Saanich Inlet, a stratified fjord in British Columbia Canada, yield sulfide oxidizing epsilonproteobacteria most closely related to Arcobacter. Physiological experiments with this Arcobacter reveal that it couples sulfide oxidation to nitrate reduction under anaerobic conditions, while metagenomic analyses reveal that it can comprise an appreciable component of the Saanich Inlet microbial community while remaining largely undetected in fingerprinting analyses. In this presentation, we will describe the metabolic and physiological potential of this Arcobacter and comment on its possible role in the ecology and biogeochemistry of OMZs.