In the methanogenic archaeon Methanosarcina barkeri Fusaro, the N 5-methyl-tetrahydrosarcinapterin (CH3-H 4SPT):coenzyme M (CoM) methyltransferase, encoded by the mtr operon, catalyzes the energy-conserving (sodium-pumping) methyl transfer from CH 3-H4SPT to CoM during growth on H2/CO 2 or acetate. However, in the disproportionate of C-1 compounds, such as methanol, to methane and carbon dioxide, it catalyzes the reverse, endergonic transfer from methyl-CoM to H4SPT, which is driven by sodium uptake. It has been proposed that a bypass for this energy-consuming reaction may occur via a direct methyl transfer from methanol to H 4SPT. To test this, an mtr deletion mutant was constructed and characterized in M. barkeri Fusaro. The mutant is unable to grow on methanol, acetate or H2/CO2, but can grow on methanol with H 2/CO2 and, surprisingly, methanol with acetate. 13C labeling experiments show that growth on acetate with methanol involves a previously unknown methanogenic pathway, in which oxidation of acetate to a mixture of CO2 and formic acid is coupled to methanol reduction. Interestingly, although the mutant is unable to grow on methanol alone, it remains capable of producing methane from this substrate. Thus, the proposed Mtr bypass does exist, but is unable to support growth of the organism.
|Original language||English (US)|
|Number of pages||6|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Jul 26 2005|
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