Hydrogen Regulation Of Growth, Growth Yields, And Methane Gene Transcription In Methanobacterium Thermoautotrophicum Delta H

Changes in growth rate, methanogenesis, growth yield (Y-CH4), and methane gene transcription have been correlated with changes in the supply of H-2 to Methanobacterium thermoautotrophicum Delta H cells growing on H-2 plus CO2 in fed-batch cultures. Under conditions of excess H-2, biomass and methanogenesis increased exponentially and in parallel, resulting in cultures with a constant Y-CH4 and transcription of the mth and mrt genes that encode the H-2-dependent N-5,N-10-methenyltetrahydromethanopterin (methenyl-H(4)MPT) reductase (MTH) and methyl coenzyme M reductase II (MRII), respectively. Reducing the H-2 supply, by decreasing the percentage of H-2 in the input gas mixture or by reducing the mixing speed of the fermenter impeller, decreased the growth rate and resulted in lower and constant rates of methanogenesis, Under such H-2-limited growth conditions, cultures grew with a continuously increasing Y-CH4 and the Mtd and mcr genes that encode the reduced coenzyme F-420-dependent N-5,N-10-methenyl-H(4)MPT reductase (MTD) and methyl coenzyme M reductase I (MRT), respectively, were transcribed. Changes in the kinetics of growth, methanogenesis, and methane gene transcription directed by reducing the H-2 supply could be reversed by restoring a high H-2 supply, Methane production continued, but at a low and constant rate, and only mcr transcripts could be detected when the H-2 supply was reduced to a level insufficient for growth, ftsA transcripts, which encode coenzyme F-390 synthetase, were most abundant in cells growing with high H-2 availability, consistent with coenzyme F-390 synthesis signaling a high exogenous supply of reductant.