ISOLATION AND CHARACTERIZATION OF METHANOBACTERIUM-THERMOAUTOTROPHICUM DELTA-H MUTANTS UNABLE TO GROW UNDER HYDROGEN-DEPRIVED CONDITIONS

By using random mutagenesis and enrichment by chemostat culturing, me have developed mutants of Methanobacterium thermoautotrophicum that me re unable to grow under hydrogen-deprived conditions. Physiological ch aracterization showed that these mutants had poorer growth rates and g rowth yields than the wild-type strain. The mRNA levels of several key enzymes mere lower than those in the wild-type strain. A fed-batch st udy showed that the expression levels mere related to the hydrogen sup ply. In one mutant strain, expression of hath methyl coenzyme M reduct ase isoenzyme I and coenzyme F-420-dependent 5,10-methylenetetrahydrom ethanopterin dehydrogenase mas impaired. The strain was also unable to form factor F-390, lending support to the hypothesis that the factor functions in regulation of methanogenesis in response to changes in th e availability of hydrogen.