Open AccessEfficiency of hydrogen utilization during unitrophic and mixotrophic growth of Acetobacterium woodii on hydrogen and lactate in the chemostat
Author(s) -
Peters V,
Janssen P.H,
Conrad R
Publication year - 1998
Publication title -
fems microbiology ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.377
H-Index - 155
eISSN - 1574-6941
pISSN - 0168-6496
DOI - 10.1111/j.1574-6941.1998.tb00516.x
Subject(s) - chemostat , dilution , biology , substrate (aquarium) , steady state (chemistry) , biochemistry , food science , zoology , bacteria , chemistry , ecology , organic chemistry , genetics , physics , thermodynamics
Acetobacterium woodii is able to grow chemolithoautotrophically on H 2 plus CO 2 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 H 2 , the bacteria were grown under substrate limitation in chemostat culture using H 2 /CO 2 or lactate for unitrophic and H 2 /CO 2 +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 H 2 /CO 2 , lactate, and H 2 /CO 2 +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, H 2 partial pressures could always be analyzed and generally increased with increasing dilution rate. It is noteworthy that steady state H 2 concentrations (11–20 Pa) were also detected in lactate‐grown chemostats demonstrating that H 2 was produced. During growth on H 2 /CO 2 residual H 2 partial pressures were much higher (50–2450 Pa, depending on dilution rate) than on lactate. Mixotrophic growth, on the other hand, resulted in intermediate H 2 partial pressures (25–160 Pa, depending on dilution rate). A similar pattern of H 2 partial pressures was obtained when the bacteria were grown at 25°C instead 30°C. Growth yields and H 2 partial pressures were not affected by the concentration of lactate (0.1–1.0 mM) under both unitrophic and mixotrophic conditions. The H 2 partial pressures at the half maximum growth rate on lactate, lactate+H 2 /CO 2 , and H 2 /CO 2 were 16, 42, and 94 Pa, respectively. These results demonstrate that A. woodii is able to utilize H 2 down to lower partial pressures when a second heterotrophic substrate is available. However, the residual H 2 partial pressures were still too high to allow successful competition with H 2 ‐utilizing methanogens.