Methanol utilization in defined mixed cultures of thermophilic anaerobes in the presence of sulfate.

We studied thermophilic sulfate reduction with methanol as electron donor in continuous cultures. Mixed cultures of selected microorganisms were used, representing different methanol degrading pathways followed by various trophic groups of microorganisms. Our results show that direct competition for methanol between a homoacetogen, Moorella thermoautotrophica, and a sulfate reducer, Desulfotomaculum kuznetsovii, is in favour of the sulfate reducer due to its affinity for methanol. Methanogenesis as a result of interspecies hydrogen transfer between D. kuznetsovii and a hydrogen-consuming methanogenic archaeon, Methanothermobacter thermoautotrophicus occurred only below 5 mM total sulfide. A similar result was obtained when M. thermoautotrophica was grown on methanol in the presence of Mb. thermoautotrophicus. Interestingly, D. kuznetsovii could coexist with a non-methanol-utilizing sulfate reducer (Thermodesulfovibrio species). Our data show that it is possible to maintain a dominant sulfate-reducing process with methanol as electron donor at 60 degrees C in mixed continuous cultures.