Geology topics

J.C. Murrell

Publications and source records attributed to J.C. Murrell.

4 recordsLinked to original sources

USGS2004

Degradation of methyl bromide and methyl chloride in soil microcosms: Use of stable C isotope fractionation and stable isotope probing to identify reactions and the responsible microorganisms

Bacteria in soil microcosm experiments oxidized elevated levels of methyl chloride (MeCl) and methyl bromide (MeBr), the former compound more rapidly than the latter. MeBr was also removed by chemical reactions while MeCl was not. Chemical degradation dominated the early removal of MeBr and accounted for more than half of its total loss. Fractionation of stable carbon isotopes during chemical degradation of MeBr resulted in a kinetic isotope effect (KIE) of 59 ± 7‰. Soil bacterial oxidation dominated the later removal of MeBr and MeCl and was characterized by different KIEs for each compound. The KIE for MeBr oxidation was 69 ± 9‰ and the KIE for MeCl oxidation was 49 ± 3‰. Stable isotope probing revealed that different populations of soil bacteria assimilated added 13 C-labeled MeBr and MeCl. The identity of the active MeBr and MeCl degrading bacteria in soil was determined by analysis of 16S rRNA gene sequences amplified from 13 C-DNA fractions, which identified a number of sequences from organisms not previously thought to be involved in methyl halide degradation. These included Burkholderia , the major clone type in the 13 C-MeBr fraction, and Rhodobacter, Lysobacter and Nocardioides the major clone types in the 13 C-MeCl fraction. None of the 16S rRNA gene sequences for methyl halide oxidizing bacteria currently in culture (including Aminobacter strain IMB-1 isolated from fumigated soil) were identified. Functional gene clone types closely related to Aminobacter spp. were identified in libraries containing the sequences for the cmuA gene, which codes for the enzyme known to catalyze the initial step in the oxidation of MeBr and MeCl. The cmuA gene was limited to members of the alpha-Proteobacteria whereas the greater diversity demonstrated by the 16S rRNA gene may indicate that other enzymes catalyze methyl halide oxidation in different groups of bacteria.

Geochimica et Cosmochimica Acta↗

USGS2002

A review of bacterial methyl halide degradation: Biochemistry, genetics and molecular ecology

Methyl halide‐degrading bacteria are a diverse group of organisms that are found in both terrestrial and marine environments. They potentially play an important role in mitigating ozone depletion resulting from methyl chloride and methyl bromide emissions. The first step in the pathway(s) of methyl halide degradation involves a methyltransferase and, recently, the presence of this pathway has been studied in a number of bacteria. This paper reviews the biochemistry and genetics of methyl halide utilization in the aerobic bacteria Methylobacterium chloromethanicum CM4 T , Hyphomicrobium chloromethanicum CM2 T , Aminobacter strain IMB‐1 and Aminobacter strain CC495. These bacteria are able to use methyl halides as a sole source of carbon and energy, are all members of the α ‐Proteobacteria and were isolated from a variety of polluted and pristine terrestrial environments. An understanding of the genetics of these bacteria identified a unique gene ( cmuA ) involved in the degradation of methyl halides, which codes for a protein (CmuA) with unique methyltransferase and corrinoid functions. This unique functional gene, cmuA , is being used to develop molecular ecology techniques to examine the diversity and distribution of methyl halide‐utilizing bacteria in the environment and hopefully to understand their role in methyl halide degradation in different environments. These techniques will also enable the detection of potentially novel methyl halide‐degrading bacteria.

Environmental Microbiology↗

USGS2002

Leisingera methylohalidivorans gen. nov., sp. nov., a marine methylotroph that grows on methyl bromide

A marine methylotroph, designated strain MB2T, was isolated for its ability to grow on methyl bromide as a sole carbon and energy source. Methyl chloride and methyl iodide also supported growth, as did methionine and glycine betaine. A limited amount of growth was observed with dimethyl sulfide. Growth was also noted with unidentified components of the complex media marine broth 2216, yeast extract and Casamino acids. No growth was observed on methylated amines, methanol, formate, acetate, glucose or a variety of other substrates. Growth on methyl bromide and methyl iodide resulted in their oxidation to CO2 with stoichiometric release of bromide and iodide, respectively. Strain MB2T exhibited growth optima at NaCl and Mg2+ concentrations similar to that of seawater. Phylogenetic analysis of the 16S rDNA sequence placed this strain in the alpha-Proteobacteria in proximity to the genera Ruegeria and Roseobacter. It is proposed that strain MB2T (= ATCC BAA-92T = DSM 14336T) be designated Leisingera methylohalidivorans gen. nov., sp. nov..

International Journal of Systematic and Evolutiona↗

USGS2001

Identification of methyl halide-utilizing genes in strain IMB-1, a methyl bromide-utilizing bacterium suggests a high degree of conservation of methyl halide-specific genes in gram-negative bacteria

Strain IMB-1, an aerobic methylotrophic member of the alpha subgroup of the Proteobacteria, can grow with methyl bromide as a sole carbon and energy source. A single cmu gene cluster was identified in IMB-1 that contained six open reading frames: cmuC, cmuA, orf146, paaE, hutI, and partial metF. CmuA from IMB-1 has high sequence homology to the methyltransferase CmuA from Methylobacterium chloromethanicum and Hyphomicrobium chloromethanicum and contains a C-terminal corrinoid-binding motif and an N-terminal methyl-transferase motif. However, cmuB, identified in M. chloromethanicum and H. chloromethanicum, was not detected in IMB-1.

Applied and Environmental Microbiology↗