Stable carbon isotope fractionation during methanogenesis is affected by the availability of substrates. The effects of different substrates on methanogen biomass, total lipid extract, biomarkers and methane under both abundant and limiting substrate conditions were studied. Methanosarcina barkeri was grown with methanol, acetate, trimethylamine (TMA) and H2/CO2, and carbon isotope fractionation in methane production was greatest with methanol, followed by H2/CO2, TMA and acetate. In contrast, biomass was isotopically lightest in M.barkeri grown on methanol, followed by TMA, H2/CO2 and acetate. Generally, fractionation was greater in cultures grown with abundant substrate availability as compared to those supplied with limiting substrate. During autotrophic growth, fractionation was greatest during slower growth for both methane and biomass production. The results of these fractionation studies under controlled laboratory conditions can be applied to the interpretation of isotopic signatures for methane and methanogen biomarkers, and ecological processes, in marine environments. Several hypersaline springs off the western shore of Lake Winnipegosis, MB support unique microbial mat communities. These low temperature springs contain water with a mean salinity as high as 6.1%. Studies were undertaken to contrast the anaerobic microbial communities of these springs, specifically the methanogens and sulphate-reducing bacteria (SRB), and their contributions to biogeochemical cycling in these mats. Comparisons of lipid profiles revealed changes in the proportions of the dominant fatty acids related to the amount of mat growth. Cultures of SRB and methanogens were established with six different substrates. Methanogenic cultures grew best on TMA and methanol, but could use formate, H2/CO2 and glycine betaine as well. In contrast, H2/CO2 was the preferred substrate of the SRB enrichment cultures, which were also able to use formate, but not TMA, the breakdown product of the compatible solute glycine betaine. Maximum methane production occurred at 5% salinity. The lipid composition of the mats, including methanogen biomarkers, and the results of the enrichments on different substrates and at different salinities, suggest that methanogenesis in these springs is supported by compatible solutes whereas sulphate reduction is linked to availability of hydrogen and formate. / February 2005

Stable carbon isotope fractionation during methanogenesis is affected by the availability of substrates. The effects of different substrates on methanogen biomass, total lipid extract, biomarkers and methane under both abundant and limiting substrate conditions were studied. Methanosarcina barkeri was grown with methanol, acetate, trimethylamine (TMA) and H2/CO2, and carbon isotope fractionation in methane production was greatest with methanol, followed by H2/CO2, TMA and acetate. In contrast, biomass was isotopically lightest in M.barkeri grown on methanol, followed by TMA, H2/CO2 and acetate. Generally, fractionation was greater in cultures grown with abundant substrate availability as compared to those supplied with limiting substrate. During autotrophic growth, fractionation was greatest during slower growth for both methane and biomass production. The results of these fractionation studies under controlled laboratory conditions can be applied to the interpretation of isotopic signatures for methane and methanogen biomarkers, and ecological processes, in marine environments. Several hypersaline springs off the western shore of Lake Winnipegosis, MB support unique microbial mat communities. These low temperature springs contain water with a mean salinity as high as 6.1%. Studies were undertaken to contrast the anaerobic microbial communities of these springs, specifically the methanogens and sulphate-reducing bacteria (SRB), and their contributions to biogeochemical cycling in these mats. Comparisons of lipid profiles revealed changes in the proportions of the dominant fatty acids related to the amount of mat growth. Cultures of SRB and methanogens were established with six different substrates. Methanogenic cultures grew best on TMA and methanol, but could use formate, H2/CO2 and glycine betaine as well. In contrast, H2/CO2 was the preferred substrate of the SRB enrichment cultures, which were also able to use formate, but not TMA, the breakdown product of the compatible solute glycine betaine. Maximum methane production occurred at 5% salinity. The lipid composition of the mats, including methanogen biomarkers, and the results of the enrichments on different substrates and at different salinities, suggest that methanogenesis in these springs is supported by compatible solutes whereas sulphate reduction is linked to availability of hydrogen and formate.

Stable carbon isotope fractionation during methanogenesis is affected by the availability of substrates. The effects of different substrates on methanogen biomass, total lipid extract, biomarkers and methane under both abundant and limiting substrate conditions were studied. Methanosarcina barkeri was grown with methanol, acetate, trimethylamine (TMA) and H2/CO2, and carbon isotope fractionation in methane production was greatest with methanol, followed by H2/CO2, TMA and acetate. In contrast, biomass was isotopically lightest in M.barkeri grown on methanol, followed by TMA, H2/CO2 and acetate. Generally, fractionation was greater in cultures grown with abundant substrate availability as compared to those supplied with limiting substrate. During autotrophic growth, fractionation was greatest during slower growth for both methane and biomass production. The results of these fractionation studies under controlled laboratory conditions can be applied to the interpretation of isotopic signatures for methane and methanogen biomarkers, and ecological processes, in marine environments. Several hypersaline springs off the western shore of Lake Winnipegosis, MB support unique microbial mat communities. These low temperature springs contain water with a mean salinity as high as 6.1%. Studies were undertaken to contrast the anaerobic microbial communities of these springs, specifically the methanogens and sulphate-reducing bacteria (SRB), and their contributions to biogeochemical cycling in these mats. Comparisons of lipid profiles revealed changes in the proportions of the dominant fatty acids related to the amount of mat growth. Cultures of SRB and methanogens were established with six different substrates. Methanogenic cultures grew best on TMA and methanol, but could use formate, H2/CO2 and glycine betaine as well. In contrast, H2/CO2 was the preferred substrate of the SRB enrichment cultures, which were also able to use formate, but not TMA, the breakdown product of the compatible solute glycine betaine. Maximum methane production occurred at 5% salinity. The lipid composition of the mats, including methanogen biomarkers, and the results of the enrichments on different substrates and at different salinities, suggest that methanogenesis in these springs is supported by compatible solutes whereas sulphate reduction is linked to availability of hydrogen and formate.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on November 1, 2007) Includes bibliographical references.

Carboxylated macromolecules such as alginate and glycoproteins are abundant components of modern shallow marine sediments where they are secreted by bacteria and marine infauna. Both organic compounds are proton and metal reactive; hence, they have the potential to facilitate metal sorption and biomineralization reactions. In this study, lab experiments were coupled to field-based sampling to assess the role that these compounds play in microbial mats, with particular emphasis on the hypersaline lagoons of Los Roques, Venezuela. Here I applied a surface complexation approach to model proton and Cd adsorption behaviour of both uronic acid-rich alginate and mucin. Measured total site concentrations, available for metal adsorption, demonstrate that these compounds have the potential to induce metal partitioning in early diagenetic microenvironments. Field results from Venezuela are consistent with Mg- and trace metal- enrichment that follows a likely correlation with the degradation states of microbial biomass trapped during accretion of modern microbialites.

No description available.

Thesis (M.S.)--University of Nevada, Reno, 2006. / "December, 2006." Includes bibliographical references (leaves 39-44). Online version available on the World Wide Web. Library also has microfilm. Ann Arbor, Mich. : ProQuest Information and Learning Company, [2006]. 1 microfilm reel ; 35 mm.

Thesis (M.S.)--Duquesne University, 2007. / Title from document title page. Abstract included in electronic submission form. Includes bibliographical references (p. 67-70) and index.

No description available.

Mature microbial mats from sandy intertidal beaches of the Texas Gulf coast demonstrated substantial levels of nitrogenase activity. Two species of non-heterocystous cyanobacteria, a Hydrocoleum and a Microcoleus, dominated the upper green layer of mature mats. Subsurface layers of cyanobacteria, but not mature mats, appeared during dry seasons. These "proto-mats" contained almost exclusively Microcoleus and demonstrated neither nitrogenase activity nor detectable nitrogenase reductase (Fe-protein). Hydrocoleum, identified from its morphology and 16s rDNA, was isolated and cultivated as unialgal cultures. Similar diel patterns of nitrogenase activity and Fe-protein expression were found in intact mature mats and in isolated Hydrocoleum cultures. Primers and a probe specific for the Hydrocoleum nifH gene, along with q-rtPCR measurements, demonstrated similar levels, but slightly different patterns, of expression in intact mature mats and cultures of isolated Hydrocoleum. Increased levels of nifH transcripts and Fe-protein in Hydrocoleum cultures appeared before the end of the light period of a diel cycle, and the light period was required for nitrogenase activity in the subsequent dark period. Levels of nifH transcripts stayed very low and nitrogen fixation stopped when cultures were maintained under continuous darkness. The pattern of nitrogenase activity in Hydrocoleum cultures was not affected by elimination of ambient O₂, increasing or decreasing temperature in a range from 20 ˚C to 35 ˚C, or light intensity. However, the level of nitrogenase activity did vary with environmental conditions. Highest nitrogenase activities were observed when assays were conducted in an aerobic rather than an anaerobic environment, at 25 ˚C rather than a higher or lower temperature, and illuminated with bright (~ 900 [mu]E/m²s¹), rather than less intense light. Average levels of nifH transcripts were positively correlated with levels of nitrogenase activity. Isolated cultures of Hydrocoleum formed mat-like structures in undisturbed flasks, suggesting that Hydrocoleum may be an early colonizer of intertidal sand for mat formation. However, observations of subsurface proto-mats indicate that Microcoleus is more likely to serve as the foundation for cyanobacterial mats, with Hydrocoleum later providing structural integrity and nitrogen availability. A process of successional development of microbial mats from the South Texas Gulf Coast is hypothesized. / text