44969-AC2
Community Succession and Hydrocarbon Oxidation in Marine Microbial Mats: An in-situ Time Series Experiment
The purpose of this project was to investigate the development of microbial mat communities at the oxic-anoxic interface in marine petroleum seeps. The experimental approach was to conduct deployments of modular surfaces in petroleum seeps, which enabled the growth of mat communities in-situ and provided a controlled sampling environment. The first successful deployment was conducted in the first year of this project.
The focus of research during the second and final year of this award was divided between three primary areas. The first area was the publication of results from initial sampling and experiments conducted as part of this project, with the result of one publication included also with this report. Two additional publications are planned in the near future. The second area was laboratory analyses of samples collected in the previous deployment. Analyses included bulk elemental and isotopic quantification for carbon, nitrogen, sulfur and hydrogen, the quantification, identification and carbon isotopic determination for membrane lipids, as well as the extraction, purification, amplification, fragment digestion and sequencing of key genes (16SrRNA and methane monooxygenase) to identify the members of the microbial community. The third area was the deployment of additional growth modules for purposes of providing fresh mat material for a manipulative laboratory experiment. This experiment involved incubating fresh mats with a headspace of methane and tracking the loss of methane over time. Incubations with 13C-labelled methane were also performed to allow tracking of methane carbon into microbial biomarkers such as DNA, RNA and lipids.
While results are still being analyzed from these experiments, we have collected sufficient data to understand the function and activity of microbial mats in these petroleum seeps. We find that methanotrophs constitute a significant fraction of the microbial population in mat communities, perhaps as much as half. The development of the communities occurs first through the growth of sulfide oxidizing autotrophs – who we discovered fix carbon dioxide from thermogenic gas. The methanotropic members of the community gradually grow in, as do heterotrophs who might be relying on waste products from the methanotrophs. Within a period of one month, methanotrophs grow in to a maximal extent, with subsequent temporal or spatial shifts in their relative importance. We have also found that winter storm events completely scour the microbial mats from the sea floor and act to reset their development. Our incubations have enabled the determination of biomass specific methanotrophic potential, and the molecular analyses are poised to reveal the identities of the dominant microbes in the mats.
Several individuals have been associated with and benefited from this project. Dr. Haibing Ding served as a postdoctoral researcher and conducted much of the work described here. Dr. Ding was recently offered a faculty position in his home country, China – partially because of his productivity enabled by this project. Two graduate students, Frank Kinnman and George Wardlaw also benefited from this project – both are anticipating receiving Ph.D. degrees in 2008. A new graduate student, Mr. Blair Paul has also benefited from this project, and has conducted the most recent incubation and isotope probing studies. Two undergraduates also benefited from this study, Ms. Sarah Stanley and Ms. Kendra Swain. Both worked on the molecular biological aspects of mat composition. Ms Stanley is continuing with this line of research for another year for her honors thesis, and Ms. Swain is now a Ph.D. student in microbiology at the University of British Columbia.
