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44969-AC2
Community Succession and Hydrocarbon Oxidation in Marine Microbial Mats: An in-situ Time Series Experiment
Microbial mats develop and thrive at the oxic-anoxic interface in marine environments, acquiring energy by the oxidation of sulfide to elemental sulfur and sulfate. Microbial mats are abundant in areas of petroleum seepage and are thought to be fueled by sulfide produced in the subsurface during anaerobic petroleum oxidation. Neither the rates at which such communities develop, the role of microbial mats in direct petroleum oxidation nor the development of these communities has been addressed previously. The goal of this project is to investigate the development of microbial mat communities and their role in petroleum oxidation through in-situ experimentation at the Coal Oil Point hydrocarbon seep field. Major milestones over the past year include the development and fabrication of a modular benthic system to cultivate microbial mat communities in seep environments, the successful deployment of the benthic system at 67 feet water depth, the successful recovery of a time series lasting nearly 4 months, and the preliminary analysis of data from the time series.
The benthic systems were constructed in the Fall of 2006, and deployed in December of 2006 at a petroleum seep located in 67 feet of water off the coast of Goleta, CA. Two systems were deployed within about 10m of each other - one in the seep and one outside the seep. Starting in January, 2007, modular surfaces (samples) were collected by scuba diver weekly through April of 2007. In April of 2007 wind storms scoured the sea floor, removing mat communities from the entire seep as well as from the benthic deployment. The mat communities were found to develop rapidly in the seep field, but not outside the seep. High levels of biomass accumulated within two weeks of deployment, owing to sulfide oxidizing bacteria. Within a month methanotrophic bacteria accounted for a large percentage of the mat community, at which time the communities appeared to oscillate irregularly in terms of dominance.
Each modular sample collected was split into several aliquots. We have begun analyzing these samples and will continue to do so for the remainder of the grant period. Analyses performed thus far include bulk elemental analysis (carbon, nitrogen, hydrogen and sulfur abundance), stable isotopic analysis of bulk material (d13C. d15N, d34S), lipid abundance, quantification of individual fatty acid concentrations as fatty acid methyl esters, quantification of d13C for individual fatty acids, and structural identification of all fatty acids - for each of the samples in the time series. Archived samples will be used to determine microbial community diversity changes (using terminal restriction fragment length polymorphism), phylogenetic identities of key organisms (using a clone library approach), and microscopic assessment of cellular identity using florescence in-situ hybridization.
In addition, we have conducted baseline investigations of additional natural mat communities for purposes of comparison. These communities were collected from the seep field where the in-situ incubation was conducted, and from other seeps where only sulfide drives chemosynthesis. These experiments contributed to a manuscript currently in review at the Journal of Geophysical Research - Biogeosciences. A second manuscript outlining the geochemical aspects of the in-situ incubation is currently in preparation.
Over the second year of this project effort will be directed toward completing molecular and microbial analyses with the archived samples. This data will be analyzed and prepared for publication. We also plan a second deployment of the remaining in-situ system, to collect material to conduct rate measurements and for other bulk analyses.
