Thermodynamic analysis of growth of Methanobacterium thermoautotrophicum

Growth of Methanobacterium thermoautotrophicum, an anaerobic archaebacteriu m using methanogenesis as the catabolic pathway, is characterized by large heat production rates, up to 13 W g(-1), and low biomass yields, in the ord er of 0.02 C-mol mol(-1) H-2 consumed. These values, indicating a possibly "inefficient" growth mechanism, warrant a thermodynamic analysis to obtain a better understanding of the growth process. The growth-associated heat pr oduction (Delta(r)H(X)(0,min)) and the growth-associated Gibbs energy dissi pation per mot biomass formed (Delta(r)G(X)(min)) were -3730 kJ C-mol(-1) a nd -802 kJ C-mol(-1), respectively. The Gibbs energy change found in this s tudy is indeed unusually high as compared to aerobic methylotrophes, but no t untypical for methanogens grown on CO2. It explains the low biomass yield . Based on the information available on the energetic metabolism and on an ATP balance, the biomass yield can be predicted to be approximately in the range of the experimentally determined value. The fact that the exothermici ty exceeds vastly even the Gibbs energy change can be explained by a dramat ic entropy decrease of the catabolic reaction. Microbial growth characteriz ed by entropy reduction and correspondingly by unusually large heat product ion may be called entropy-retarded growth. (C) 1999 John Wiley & Sons, Inc.