ISSN:
1574-6941
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Biology
Notes:
Methanogens and homoacetogens compete for available H2 in anoxic environments. The competitiveness of these microorganisms was studied by measuring H2 consumption kinetics (Vmax, Km, threshold) in different psychroactive strains as function of temperature. Methanogenic strains MSB and MSP and homoacetogenic Acetobacterium bakii, A. paludosum, A. fimetarium, A. tundrae, which were isolated from different low-temperature environments, were all able to grow and consume H2 in a temperature range of 4–30°C. The H2 thresholds steadily decreased with decreasing temperature in cultures of A. bakii, A. tundrae and strain MSB. In A. paludosum, A. fimetarium and especially in strain MSP, however, H2 thresholds again increased below 10–15°C. With exception of strain MSP at ≤10°C, H2 thresholds were generally lower in the methanogens (〈2 Pa H2) than homoacetogens (〈200 Pa H2). 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 H2 consumption, i.e. approximately −5 to −8 kJ mol−1, being similar for methanogens and homoacetogens. Vmax 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. Km also increased with temperature and was higher in A. bakii (about 190–520 Pa H2) than in the methanogens (about 50–190 Pa H2). The values of H2 threshold, Vmax and Km, 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 H2 at high H2 concentrations because of higher Vmax. It also outcompeted the methanogenic strain MSP at low H2 and low temperature. However, the capacity of the methanogens to compete with A. bakii for H2 increased with decreasing H2 concentration because of more favorable Km and threshold. In the methanogenic strain MSB, the H2 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.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1574-6941.2001.tb00893.x
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