M. thermoautotrophicum was grown on a defined mineral salts medium under strictly anaerobic conditions with H2 and CO2 as the sole energy and C source, resp. The cultivation medium was optimized with respect to inorg. components, including Se(IV), W(VI), N, Ni(II), Fe(II), Co(II), and Mo(VI). S2- concn. in the medium was maintained const. using an online regulatory system by the addn. of 0.5M Na2S. A max. supply rate of 0.6 VVM of a mixt. of 80% H2 and 20% CO2 was achieved for the gaseous substrates. Under these conditions, the max. sp. growth rate (m) was 0.30/h and the cell concn. reached 4.8 g cell dry wt./L, representing a 140% increase over previously published results, in <20 h. At the end of the culture, the prodn. of CH4 was stationary at 0.09 VVM, corresponding to a substrate conversion of 75%. [on SciFinder (R)]