Competition between homoacetogenic bacteria and methanogenic archaea for hydrogen at low temperature

Methanogens and homoacetogens compete for available H(2) in anoxic environments. The competitiveness of these microorganisms was studied by measuring H(2) consumption kinetics (V(max), K(m), threshold) in different psychroactive strains as function of temperature, Methanogenic strains MSB and MSP and homoacetogenic Acetobacterium bakii, A. paludosum, A. fimertarium, A. tundrae, which were isolated from different low-temperature environments, were all able to grow and consume H(2) in a temperature range of 4-30degreesC. The H(2) thresholds steadily decreased with decreasing temperature in cultures of A. bakii, A. tundrae and strain MSB. In A. paludosum, A. fimertarium and especially in strain MSP, however, H(2) thresholds again increased below 10-15degreesC. With exception of strain MSP at less than or equal to10degreesC, H(2) thresholds were generally lower in the methanogens (< 2 Pa H(2)) than homoacetogens (< 200 Pa H(2)). The measured thresholds decreased in parallel to those predicted from thermodynamic theory, and thus allowed the calculation of a critical Gibbs' free energy required for H(2) consumption, i.e. approximately -5 to -8 W mol(-1), being similar for methanogens and homoacetogens. V(max) increased with temperature. The increase was more pronounced in the methanogenic strains than in A. bakii, but the values of the latter were generally higher K(m) also increased with temperature and was higher in A. bakii (about 190-520 Pa H(2)) than in the methanogens (about 50-190 Pa H(2)). The values of H(2) threshold, V(max) and K(m), were used to compare the relative competitiveness of the different microorganisms over the entire temperature range Using a kinetic model. A. bakii revealed a generally strong competitiveness for H(2) at high H(2) concentrations because of higher V(max). It also outcompeted the methanogenic strain MSP at low H(2) and low temperature. However, the capacity of the methanogens to compete with A. bakii for H(2) increased with decreasing H(2) concentration because of more favorable K(m) and threshold. In the methanogenic strain MSB, the H(2) thresholds were generally lower than those of the homoacetogens irrespective of the temperature, and thus it outcompeted A. bakii. Methanogenic strain MSP, on the other hand, was outcompeted by A. bakii at low temperature because of insufficient psychrotolerance. (C) 2001 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.