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.