LLE: Life Electric: Interactions, physiology, and ecosystem impact of cooperative microbial methane-oxidation in anoxic deep ocean sediments

Anaerobic oxidation of methane (AOM) is a globally significant methane sink in the ocean. It is mediated by slow-growing microorganisms that have been challenging to culture in the laboratory. In deep-sea cold seeps, where methane is advected to the seabed, AOM is largely mediated through syntrophic relationships between diverse methane-oxidizing archaea (ANME) and sulfate-reducing bacteria (SRB). We have found that these syntrophs form highly structured consortia and appear to cooperate metabolically through a process known as direct interspecies electron transfer. These consortia serve as ecosystem engineers in the seep environment. They change the local chemistry and ecology through the active production of chemosynthetic substrates like hydrogen sulfide, and they alter the physical landscape through the conversion of methane into authigenic carbonate rocks, paving large areas of the seafloor. Despite the global importance of these methane-oxidizing syntrophs, fundamental aspects of their physiology, community ecology, and evolution remain poorly resolved. In this presentation, I will highlight our geobiological research on these enigmatic methane-oxidizing partnerships in seep sediments and carbonates and chemical strategies to manipulate this microbial metabolic partnership in the laboratory. Through the integration of metagenomic sequencing targeting single consortia, in tandem with transcriptomics and the application of spatially resolved single cell stable isotope analysis by nanoSIMS and click chemistry-based activity tracers (BONCAT), we are building new understanding about the network of microbial interactions and metabolic potential shaping these productive methane-fueled deep ocean ecosystems.

Speaker Bio:

Victoria J. Orphan is the James Irvine Professor of Environmental Science and Geobiology in the Divisions of Geological and Planetary Science and Biology and Biological Engineering at Caltech. Orphan’s multidisciplinary research program spans the interface between environmental microbiology, geochemistry, and geology. Through the integrated application of environmental ‘omics approaches, stable isotope analysis, and imaging, her group is characterizing the interspecies interactions and ecological physiology of archaea, bacteria, and viruses linked to the cycling of methane, sulfur, nitrogen, and metals in ocean sediments and extreme environments. Orphan received her B.A. in 1994 and Ph.D. in 2001 from the University of California, Santa Barbara, in the ecology, evolution and marine biology program. Prior to joining the faculty at Caltech in 2004, she was a National Research Council fellow at the NASA Ames research center. She is the director of Caltech’s Kerckhoff Marine laboratory and the Center for Environmental Microbial Interactions (CEMI). She is a fellow of the American Geophysical Union and American Academy of Microbiology, a member of the American Academy of Arts and Sciences and was named a MacArthur Fellow in 2016.