Methanosarcina barkeri

About: Methanosarcina barkeri is a research topic. Over the lifetime, 703 publications have been published within this topic receiving 32151 citations.

Biosynthesis of Methane from the Methyl Moiety of Methylcobalamin in Extracts of Methanosarcina Barkeri

Abstract: Methanol is reduced to methane, according to reaction 1, by a mechanism not involving equilibration with carbon dioxide in the system.2 When C14-labeled acetate is fermented by M . barkeri (reaction 2 ) the methane is derived almost exclusively from the methyl carbon and the carboxyl carbon is converted to carbon dioxide.3~~ In studies with deuterium-labeled substrates it was f ~ u n d ~ , ~ that the methyl moieties of both methanol and acetate are transformed to methane without loss of any deuterium. The recent discovery of Guest et aZ.7 that methylcobalamin can serve as methyl donor to homocysteine to form methionine, suggested that these observations might all be explained by an enzymic transfer of the methyl moiety of the fermented substrates to a cobamide compound forming a methyl-B12 type derivative followed by a cleavage yielding methane. In preliminary experiments to test this hypothesis, substrate level amounts of methylcobalamin were added to broken cell preparations of Methanosarcina barkeri to see if it could serve as a source of methane. On the assumption that an external reducing agent might be required to form methane from methyl-B12, pyruvate was added as electron donor. In experiment 1 of TABLE 1 it can be seen that 2.3 pmoles of methane were produced in a sample containing 3 pmoles of methyl-BI2 and 30 pmoles of pyruvate. If the methyl derivative was replaced with 3 pmoles of cyano-vitamin BIZ, no methane was formed. In experiment 2, the yield of methane is seen to parallel the amount of methyl-B12 added and finally, in experiment 3, the dependency on pyruvate is illustrated. To establish that the methyl moiety of methylcobalamin is actually transformed to methane, similar experiments were conducted using the C4-methyl-labeled derivative (TABLE 2 ) . Unlabeled pyruvate (30 pmoles) was present in all of these samples. Aliquots of the gas phase, freed of carbon dioxide by equilibration with alkali, were combusted over hot

Antigenic mosaic of Methanosarcinaceae: partial characterization of Methanosarcina barkeri 227 surface antigens by monoclonal antibodies.

Abstract: Hybridomas were constructed with spleen cells from mice immunized against Methanosarcina barkeri 227. The reaction with the resulting monoclonal antibodies identified two antigenic determinants. Determinant 8A is present in M. barkeri 227, where it is accessible to antibody on whole bacterial cells. 8A is undetectable in (or absent from) M. barkeri R1M3, an immunologically closely related strain. Determinant 8C is present in both strains, but with M. barkeri 227 it is found only in extracts and cannot be demonstrated in whole cells. It therefore appears to be hidden. A soluble form of antigen 8A (antigen 227) was obtained treating whole M. barkeri 227 cells with absolute methanol. This antigen was further purified by affinity chromatography with antibody 8A. Chemical and immunochemical analyses of these preparations showed that antigen 227 is a high-molecular-weight (4 X 10(5)) structure composed mainly of one carbohydrate, glucose, and small amounts of amino acids. Its solubility properties suggest that this molecule is associated with a lipid moiety.

Putative Extracellular Electron Transfer in Methanogenic Archaea.

Abstract: It has been suggested that a few methanogens are capable of extracellular electron transfers. For instance, Methanosarcina barkeri can directly capture electrons from the coexisting microbial cells of other species. Methanothrix harundinacea and Methanosarcina horonobensis retrieve electrons from Geobacter metallireducens via direct interspecies electron transfer (DIET). Recently, Methanobacterium, designated strain YSL, has been found to grow via DIET in the co-culture with Geobacter metallireducens. Methanosarcina acetivorans can perform anaerobic methane oxidation and respiratory growth relying on Fe(III) reduction through the extracellular electron transfer. Methanosarcina mazei is capable of electromethanogenesis under the conditions where electron-transfer mediators like H2 or formate are limited. The membrane-bound multiheme c-type cytochromes (MHC) and electrically-conductive cellular appendages have been assumed to mediate the extracellular electron transfer in bacteria like Geobacter and Shewanella species. These molecules or structures are rare but have been recently identified in a few methanogens. Here, we review the current state of knowledge for the putative extracellular electron transfers in methanogens and highlight the opportunities and challenges for future research.

Expanding the Genetic Code for a Dinitrophenyl Hapten.

Abstract: Haptens, such as dinitrophenyl (DNP) are small molecules that induce strong immune responses when attached to proteins or peptides and, as such, have been exploited for diverse applications. We engineered a Methanosarcina barkeri pyrrolysyl-tRNA synthetase (mbPylRS) to genetically encode a DNP-containing unnatural amino acid, N(6) -(2-(2,4-dinitrophenyl)acetyl)lysine (DnpK). Although this moiety was unstable in Escherichia coli, we found that its stability was enhanced in mammalian HEK 293T cells and was able to induce selective interactions with anti-DNP antibodies. The capability of genetically introducing DNP into proteins is expected to find broad applications in biosensing, immunology, and therapeutics.