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Methanosarcina barkeri strain 227 produced ethane during growth on H2/CO2 when ethanol was added to the medium in concentrations of 89–974 mM; ethane production varied from 14 to 38 nmoles per tube (20 ml gas phase, 5.7 ml liquid) with increasing ethanol concentrations. Cells grown to mid-logarithmic phase (A600 ∼0.46, protein = 64 μg/ml) on H2/CO2, thoroughly flushed with H2/CO2, then exposed to ethanol, produced maximal ethane levels (at 585 and 974 mM ethanol) of about 215 nmoles per tube, with an ethane/methane ratio of 1×10-3. Mid-logarithmic-phase cultures of Methanosarcina barkeri strain Fusaro also produced ethane (up to 20 nmoles per tube) when exposed to ethanol. Cultures of strain 227 growing on methanol in the absence of H2 produced ≦6 nmoles per tube of ethane when supplemented with ethanol whereas those lacking ethanol but containing H2 and/or methanol produced ≦1.6 nmoles per tube. Cultures of Methanococcus deltae strains ΔLH and ΔRC, Methanospirillum hungatei or Methanobacterium thermoautotrophicum produced ≦5 nmoles ethane per tube when grown in medium containing ethanol. Ethanol concentrations of 177–886 mM were inhibitory to growth of all methanogens examined. Production of ethane by Methanosarcina was inhibited by >62 mM methanol, and both methanogenic inhibitors tested, CCl4 and Br−CH2−CH2−SO inf3 sup- , inhibited ethane and methane production concurrently. The data suggest that ethanol is converted to ethane by Methanosarcina species using the terminal portion of the methanol-to-methane pathway.
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