Sulfate-Dependent Interspecies H2 Transfer between Methanosarcina barkeri and Desulfovibrio vulgaris during Coculture Metabolism of Acetate or Methanol

We compared the metabolism of methanol and acetate when Methanosarcina barkeri was grown in the presence and absence of Desulfovibrio vulgaris. The sulfate reducer was not able to utilize methanol or acetate as the electron donor for energy metabolism in pure culture, but was able to grow in coculture. Pure cultures of M. barkeri produced up to 10 μmol of H2 per liter in the culture headspace during growth on acetate or methanol. In coculture with D. vulgaris, the gaseous H2 concentration was ≤2 μmol/liter. The fractions of 14CO2 produced from [14C]methanol and 2-[14C]acetate increased from 0.26 and 0.16, respectively, in pure culture to 0.59 and 0.33, respectively, in coculture. Under these conditions, approximately 42% of the available electron equivalents derived from methanol or acetate were transferred and were utilized by D. vulgaris to reduce approximately 33 μmol of sulfate per 100 μmol of substrate consumed. As a direct consequence, methane formation in cocultures was two-thirds that observed in pure cultures. The addition of 5.0 mM sodium molybdate or exogenous H2 decreased the effects of D. vulgaris on the metabolism of M. barkeri. An analysis of growth and carbon and electron flow patterns demonstrated that sulfate-dependent interspecies H2 transfer from M. barkeri to D. vulgaris resulted in less methane production, increased CO2 formation, and sulfide formation from substrates not directly utilized by the sulfate reducer as electron donors for energy metabolism and growth.