Efficiency of hydrogen utilization during unitrophic and mixotrophic growth of Acetobacterium woodii on hydrogen and lactate in the chemostat

• Published in: FEMS microbiology ecology Vol. 26; no. 4; pp. 317 - 324
• Main Authors: Peters, V., Janssen, P.H., Conrad, R.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-08-1998; Blackwell; Oxford University Press
• Subjects: Acetate; Acetic acid; Acetobacterium woodii; Bacteria; Bacteriology; Biological and medical sciences; Carbon dioxide; Chemostats; Continuous culture; Dilution; Ecology; Fundamental and applied biological sciences. Psychology; Growth rate; Growth yield; Heat treating; Homoacetogenesis; Hydrogen; Lactate; Lactic acid; Metabolism. Enzymes; Methanogenic bacteria; Microbiology; Steady state; Substrates; Threshold; Homoacetogenesis; Acetate; Lactate; Hydrogen; Growth yield; Threshold; Lactates; Microorganism growth; Substrate specificity; Acetobacterium woodii; Bacteria; Acetogenesis; Chemostat
• ISSN: 0168-6496; 1574-6941
• DOI: 10.1111/j.1574-6941.1998.tb00516.x

Abstract
Acetobacterium woodii is able to grow chemolithoautotrophically on H2 plus CO2 or heterotrophically on lactate by forming acetate as sole product (homoacetogenesis). In order to investigate the effect of a second substrate on the utilization of H2, the bacteria were grown under substrate limitation in chemostat culture using H2/CO2 or lactate for unitrophic and H2/CO2+lactate for mixotrophic growth. The chemostat was run at different dilution rates (0.007–0.035 h−1) until steady state was reached. Substrate consumption was balanced by production of acetate and biomass (96–115% recovery). Growth yields increased with increasing dilution rates giving maximum values of 7.7, 9.6, and 9.6 g-dw bacteria per mol acetate produced for growth on H2/CO2, lactate, and H2/CO2+lactate, respectively. The maintenance coefficients (expressed as acetate production) were 0.4, 0.08 and 0.17 mmol g-dw−1 h−1, respectively. Residual concentrations of lactate were usually below the detection limit (5 μM). However, H2 partial pressures could always be analyzed and generally increased with increasing dilution rate. It is noteworthy that steady state H2 concentrations (11–20 Pa) were also detected in lactate-grown chemostats demonstrating that H2 was produced. During growth on H2/CO2 residual H2 partial pressures were much higher (50–2450 Pa, depending on dilution rate) than on lactate. Mixotrophic growth, on the other hand, resulted in intermediate H2 partial pressures (25–160 Pa, depending on dilution rate). A similar pattern of H2 partial pressures was obtained when the bacteria were grown at 25°C instead 30°C. Growth yields and H2 partial pressures were not affected by the concentration of lactate (0.1–1.0 mM) under both unitrophic and mixotrophic conditions. The H2 partial pressures at the half maximum growth rate on lactate, lactate+H2/CO2, and H2/CO2 were 16, 42, and 94 Pa, respectively. These results demonstrate that A. woodii is able to utilize H2 down to lower partial pressures when a second heterotrophic substrate is available. However, the residual H2 partial pressures were still too high to allow successful competition with H2-utilizing methanogens.