Microbiology of Methanogenesis in Thermal, Volcanic Environments

Publisher Website
Google Scholar
Abstract
Microbial methanogenesis was examined in thermal waters, muds and decomposing algal-bacterial mats associated with volcanic activity in Yellowstone National Park, USA. Radioactive tracer studies with [14C]glucose, acetate or carbonate and enrichment culture techniques demonstrated that methanogenesis occurred at temperatures near 70.degree. C but below 80.degree. C and correlated with H2 production from either geothermal processes or microbial fermentation. Three Methanobacterium thermoautotrophicum strains (YT1, YTA and YTC) isolated from diverse volcanic habitats differed from the neotype sewage strain .DELTA.H in DNA G-plus-C content and immunological properties. Microbial methanogenesis was characterized in more detail at a 65.degree. C site in the Octopus Spring algal-bacterial mat ecosystem. Here methanogenesis was active, was associated with anaerobic microbial decomposition of biomass, occurred concomitantly with detectable microbial H2 formation, and displayed a temperature activity optimum near 65.degree. C. Enumeration studies estimated more than 109 chemoorganotrophic hydrolytic bacteria and 106 chemolithotrophic methanogenic bacteria/g (dry wt) of algal-bacterial mat. Enumeration, enrichment and isolation studies revealed that the microbial population was predominantly rod shaped and asporogenous. A prevalent chemoorganotrophic organism in the mat that was isolated from an end dilution tube was a taxonomically undescribed gram-negative obligate anaerobe (strain HTB2), whereas a prevalent chemolithotrophic methanogen isolated from an end dilution tube was identified as M. thermoautotrophicum (strain YTB). Taxonomically recognizable obligate anaerobes that were isolated from glucose and xylose enrichment cultures included Thermoanaerobium brockii strain HTB and Clostridium thermohydrosulfuricum strain 39E. The nutritional properties, growth temperature optima, growth rates, and fermentation products of thermophilic bacterial strains 39E, HTB2 and YTB were determined.