Investigations on methane and methanotrophic bacteria in geothermally active Yellowstone Lake
Abstract
The presence of sublacustrine geothermal activity in Yellowstone Lake, Yellowstone National Park, WY has resulted in an interesting freshwater ecosystem. Analyses of bulk lake and hydrothermal vent water have indicated that vent emanations contain increased levels of mineral nutrients and gases, which, similar to marine hydrothermal emanations, are capable of supporting diverse microbial communities. The data presented in this dissertation pertains to the distribution and concentration of methane in the hydrothermal features and water columns of Yellowstone Lake and the relative size and distribution of methanotroph communities within these features of geothermally active Mary Bay. Additionally, the methanotrophic community structure of selected vents within this basin will be discussed. The chemical constituents of hydrothermal fluids from Yellowstone Lake were known to be variable. Although many areas of the lake were shown to have hydrothermal activity, the concentration of methane in a given vent's fluid varied with respect to the basin in which that vent was located. Methane levels in vent fluids from the West Thumb were typically low, while vent fluids from the lake's northeastern basins, including Mary Bay, Sedge Bay, and the canyons off Stevenson Island, were significantly higher. Despite this variability, lake basins containing geothermal activity were shown to have increased methane concentrations in their water columns when compared to the Southeast Arm, a basin having no known geothermal activity. Based on the variable methane concentrations observed and the chemical and temperature gradients established by hydrothermal venting and thermal stratification of the lake, it was assumed that varying numbers of methanotrophs would be present within the fluids of different vents and at different depths within the water column. The differences observed between individual vents with respect to methane levels and temperature should also have resulted in different methanotrophic vent communities. Primers directed at a gene found in almost all known methanotrophs, the pmo A gene, confirmed their presence in both the water column and vent fluids of Mary Bay. Utilizing these primers in conjunction with serial dilutions and most probable number (MPN) methodology, the numbers of methanotrophs present in samples from Mary Bay were shown to vary between individual vents and within the water column. These variations in methanotroph numbers could not be attributed to any measured parameter of the individual vents or depths in the water column. Overall, the data indicated that the vents and water columns of the northern basins of Yellowstone Lake contained higher concentrations of methane than the rest of the lake and that the geothermal activity of a basin could influence the methane concentration of its water column. In geothermally active Mary Bay, vent waters were shown to support greater numbers of methane-oxidizing bacteria than the water column. The methanotroph communities of these fluids were demonstrated to be diverse and influenced by the nature of the vent's emanations. The data indicated that molecular techniques were useful to describe and enumerate methanotrophs in aquatic environments. (Abstract shortened by UMI.)
This paper has been withdrawn.