Hydrogen and carbon isotope fractionation during degradation of chloromethane by methylotrophic bacteria

Chloromethane (CH3Cl) is a widely studied volatile halocarbon involved in the destruction of ozone in the stratosphere. Nevertheless, its global budget still remains debated. Stable isotope analysis is a powerful tool to constrain fluxes of chloromethane between various environmental compartments which involve a multiplicity of sources and sinks, and both biotic and abiotic processes. In this study, we measured hydrogen and carbon isotope fractionation of the remaining untransformed chloromethane following its degradation by methylotrophic bacterial strains Methylobacterium extorquens CM4 and Hyphomicrobium sp. MC1, which belong to different genera but both use the cmu pathway, the only pathway for bacterial degradation of chloromethane characterized so far. Hydrogen isotope fractionation for degradation of chloromethane was determined for the first time, and yielded enrichment factors (epsilon) of -29 parts per thousand and -27 parts per thousand for strains CM4 and MC1, respectively. In agreement with previous studies, enrichment in C-13 of untransformed CH3Cl was also observed, and similar isotope enrichment factors (e) of -41 parts per thousand and -38 parts per thousand were obtained for degradation of chloromethane by strains CM4 and MC1, respectively. These combined hydrogen and carbon isotopic data for bacterial degradation of chloromethane will contribute to refine models of the global atmospheric budget of chloromethane

Tetrachloromethane-degrading bacterial enrichment cultures and isolates from a contaminated aquifer

The prokaryotic community of a groundwater aquifer exposed to high concentrations of tetrachloromethane (CCl₄) for more than three decades was followed by terminal restriction fragment length polymorphism (T-RFLP) during pump-and-treat remediation at the contamination source. Bacterial enrichments and isolates were obtained under selective anoxic conditions, and degraded 10 mg·L(-1) CCl₄, with less than 10% transient formation of chloroform. Dichloromethane and chloromethane were not detected. Several tetrachloromethane-degrading strains were isolated from these enrichments, including bacteria from the Klebsiella and Clostridium genera closely related to previously described CCl₄ degrading bacteria, and strain TM1, assigned to the genus Pelosinus, for which this property was not yet described. Pelosinus sp. TM1, an oxygen-tolerant, Gram-positive bacterium with strictly anaerobic metabolism, excreted a thermostable metabolite into the culture medium that allowed extracellular CCl₄ transformation. As estimated by T-RFLP, phylotypes of CCl₄-degrading enrichment cultures represented less than 7%, and archaeal and Pelosinus strains less than 0.5% of the total prokaryotic groundwater community

Practical Application of Methanol-Mediated Mutualistic Symbiosis between Methylobacterium Species and a Roof Greening Moss, Racomitrium japonicum

Bryophytes, or mosses, are considered the most maintenance-free materials for roof greening. Racomitrium species are most often used due to their high tolerance to desiccation. Because they grow slowly, a technology for forcing their growth is desired. We succeeded in the efficient production of R. japonicum in liquid culture. The structure of the microbial community is crucial to stabilize the culture. A culture-independent technique revealed that the cultures contain methylotrophic bacteria. Using yeast cells that fluoresce in the presence of methanol, methanol emission from the moss was confirmed, suggesting that it is an important carbon and energy source for the bacteria. We isolated Methylobacterium species from the liquid culture and studied their characteristics. The isolates were able to strongly promote the growth of some mosses including R. japonicum and seed plants, but the plant-microbe combination was important, since growth promotion was not uniform across species. One of the isolates, strain 22A, was cultivated with R. japonicum in liquid culture and in a field experiment, resulting in strong growth promotion. Mutualistic symbiosis can thus be utilized for industrial moss production

Various microbial communities reduce methane efflux from Håkon Mosby Mud Volcano

Sediments of Håkon Mosby Mud Volcano (HMMV) are characterized by different microbial communities, which are oxidizing methane that is advectively transported to the sediment surface. Combined molecular and geochemical data reveal the presence of anaerobic oxidation of methane (AOM) in Beggiatoa and Pogonophera sediment areas whereas aerobic oxidation of methane is observed in the thermal center of HMMV. The activity is limited in each case to a narrow subsurface sediment horizon whereas the deeper layers are mostly inactive. Evidence for AOM is provided by lipid biomarker and fluorescence in situ hybridization (FISH) analyses, targeting microbial consortia of sulfate-reducing bacteria and methanotrophic archaea. The archaea detected could be assigned to a new group affiliated with Methanosarcinales, which is distinct from known phylogenetic groups involved in AOM (i.e., ANME1, ANME2). Comparative analyses show a correlating vertical distribution pattern with a sharp decline of sulfate concentration, biomarker concentration, aggregate number and AOM rate. A similar biogeochemical scenario is observed at the thermal center where, in contrast, aerobic methanotrophic gamma-proteobacteria dominate the microbial community. Biomarker analyses suggest that these bacteria are close relatives of known Methylomonas species. Without the processes of methane oxidation, the emission of methane to the hydrosphere would be even greater. Thus, the activity of the various microbial communities is an effective biological filter for methane seepage at HMMV