Thermodynamic analysis of growth of Methanobacterium thermoautotrophicum

Abstract

Growth of Methanobacterium thermoautotrophicum, an anaerobic archaebacterium 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 order 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 production (⌬ r H X 0,min ) and the growth-associated Gibbs energy dissipation per mol biomass formed (⌬ r G X min ) were −3730 kJ C-mol −1 and −802 kJ C-mol −1 , respectively. The Gibbs energy change found in this study is indeed unusually high as compared to aerobic methylotrophes, but not untypical for methanogens grown on CO 2 . 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 exothermicity exceeds vastly even the Gibbs energy change can be explained by a dramatic entropy decrease of the catabolic reaction. Microbial growth characterized by entropy reduction and correspondingly by unusually large heat production may be called entropy-retarded growth.

Biothermodynamics of live cells: a tool for biotechnology and biochemical engineering

“…In the way of an example at the opposite extreme, the catabolism of autotrophic methanogenesis leads to a reduction of chemical entropy in the medium, which has to be overcome by an overly negative enthalpic driving force. These growth processes are therefore very exothermic [52] and could be called entropy retarded.…”

Perspectives on biotechnological applications of archaea

“…Rinker et al (1999) cultivated the hyperthermophilic heterotrophs Metallosphera sedula, P. furiosus and Thermococcus litoralis in a chemostat (Table 2) and observed the production of exopolysaccharides. Continuous cultures of Methanobacterium thermoautotrophicum were performed at different gassing rates using continuous measurements of the growth-limiting factor H 2 , and a simple unstructured mathematical model was developed and verified (Schill et al 1999). Another extremely thermophilic methanogen, Methanococcus jannaschii, was grown in continuous culture to evaluate the correlation between hydrogenase activity and parameters such as growth rate and pressure (Tsao et al 1994).…”

Expanded thermodynamic model for microbial true yield prediction

“…Prediction of bacterial yield has been the focus of numerous studies (Heijnen and Roels, 1981;McCarty, 1965;Roels, 1980;Roels, 1983). The method of McCarty (McCarty, 1965, 1969, 1971, 1972a,b, 1975Rittmann and McCarty, 2001) has been widely used in environmental engineering (see for example: Alvarez et al, 1994;Arcangeli and Arvin, 1999;Beller et al, 1996;Burland and Edwards, 1999;Corseuil and Weber, 1994;Edwards and Grbic-Galic, 1994;Hayes et al, 1998;Hooker et al, 1994;Muller et al, 2003;Noguera et al, 1988;Nowak et al, 1999;Schill et al, 1999;Woo and Rittmann, 2000;Zitomer, 1998). This method was expanded by VanBriesen and Rittmann (2000) to predict step-wise yields for multi-step biodegradation reactions.…”