Victoria Orphan, Ph.D.
California Institute of Technology
Division of Geological and Planetary Sciences
Role of methane-consuming microbial symbiosis in nutrient cycling and trophic structuring
of cold seep sediment and carbonate ecosystems in the deep sea
Wednesday — June 13, 2012
Pacific Forum — 3:00 p.m.
The ability to decipher the metabolic roles of microorganisms within living microbial ecosystems and to connect microbial metabolism with biosignatures preserved in the rock record represents some of the grand challenges in the field of Microbial Geobiology. The combination of molecular methods with stable isotope analysis (both natural abundance and as tracers) in modern environments represents a multidisciplinary approach that has been used successfully to characterize links between specific microorganisms and their ecophysiology in situ.
In particular, the introduction of micron-scale isotopic analyses by secondary ion mass spectrometry (SIMS and nanoSIMS) to the study of microorganisms has enabled an unprecedented level of inquiry into the inner workings of microbial ecosystems. Integrating SIMS-based stable isotope analysis with microscopy and culture-independent metagenomics techniques, we have been investigating carbon and nutrient utilization by deep-sea microorganisms and symbiotic microbial consortia fuelled by methane in sediments and associated authigenic carbonates. Single cell characterization of methane-cycling archaea and sulphate-reducing bacteria have revealed significant inter- and intra-group heterogeneity in both stable carbon isotopic signatures and nitrogen utilization, including differences in nitrogen fixation and assimilatory nitrate reduction. These cell-specific analyses have yielded new information regarding the isotopic variability, metabolic potential and interactions between individual microorganisms and the greater biological community in methane-based ecosystems.