Js. Liu et al., Microbial growth by a net heat up-take: A calorimetric and thermodynamic study on acetotrophic methanogenesis by Methanosarcina barkeri, BIOTECH BIO, 75(2), 2001, pp. 170-180
To answer the intriguing question whether or not endothermic microbial grow
th exists, and in particular, to verify Heijnen and van Dijken's prediction
(1992), acetotrophic methanogen, Methanosarcina barkeri, has been cultivat
ed in a highly sensitive bench-scale calorimeter (an improved Bio-RC1 react
ion calorimeter) in a pH auxostat fashion. A growth yield of 0.043 C-mol C-
mol(-1) has been obtained and a cell density as high as 3 g L-1 was attaine
d. Heat uptake during growth has indeed been quantitatively measured with c
alorimetry, resulting in a heat yield of +145 kJ C-mol(-1). Thermodynamics
of the growth of acetotrophic methanogens was analyzed in detail. The chang
es in Gibbs energy, enthalpy, and entropy during growth of M. barkeri were
compared with some typical aerobic and anaerobic growth processes of differ
ent microorganisms on various substrates. In the growth of M. barkeri on ac
etate, the retarding effect of the positive enthalpy change on the driving
force of growth is overcompensated by the large positive entropy change, re
sulting from converting one organic molecule acetic acid) to two gaseous pr
oducts, CH4 and CO2. Both the enthalpy and the entropy increases are due pa
rtially to the transition of these two products into the gaseous phase. The
thermodynamic role of this phase transition for the growth process is anal
yzed. Microbial growth characterized by enthalpy increase and corresponding
ly by a large increase in entropy may be called enthalpy-retarded growth. (
C) 2001 John Wiley & Sons, Inc.