Characterization of microbial communities associated with hydrocarbon seeps

Methane seeps can provide an abundant source of energy allowing multitudes of life to take hold. Recent insights into the microbial activity at such sites has suggested that methane-oxidizing bacteria are key to redirecting would be methane emissions into microbial mats. We analyzed the microbial community structure and function with depth at methane seeps where oxygen is present. Three hydrocarbon seeps were sampled by diver acquired push cores in the shallow, oxygen-rich waters at Coal Oil Point seep field offshore of Goleta, CA: Shane, Farrar, Superseep IV. Cores were taken from the microbial mats and underlying sediments at each seep and DNA was extracted at every inch of sediment depth. A second core was later taken from one of the seeps to examine seasonal variation. There were large variations in microbial communities as a function of sediment depth with major phyla being Proteobacteria, Atribacteria, Actinobacteria, Chloroflexi, and Deferribacteres. Using a modified version of the publicly-available PAPRICA metagenome prediction tool, function was inferred for the microbial community and collapsed into metabolic pathways. A majority of metabolic pathways were unaffected by depth, whereas changes in sulfur and methane metabolisms saw an inverted relationship as expected in marine sediment environments. Predicted genes were present for both methane production (Wood-Ljundahl) and methane oxidation via methane monooxygenases that may contribute to the carbon sequestered into these microbial mats. Seasonal resampling showed that trends between different metabolisms was largely conserved. Despite being in an oxygen-rich environment, microbial communities contained many strict anaerobes that also increased in abundance at depth. This rapid decrease in oxygen is indicative of rich metabolic activity, reinforcing how effective the microbial community can be at utilizing and distributing C1 carbon within these microbial mats.