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Appl. Environ. Microbiol., Sep 1997, 3345-3351, Vol 63, No. 9
Copyright © 1997, American Society for Microbiology

The Low Biomass Yields of the Acetic Acid Bacterium Acetobacter pasteurianus Are Due to a Low Stoichiometry of Respiration-Coupled Proton Translocation

MAH Luttik, R Van Spanning, D Schipper, JP Van Dijken and JT Pronk
Department of Microbiology and Enzymology, Kluyver Laboratory of Microbiology, Delft University of Technology, 2628 BC Delft, Department of Microbiology, Free University of Amsterdam, 1081 HV Amsterdam, and Gist-brocades NV, 2600 MA Delft, The Netherlands

Growth energetics of the acetic acid bacterium Acetobacter pasteurianus were studied with aerobic, ethanol-limited chemostat cultures. In these cultures, production of acetate was negligible. Carbon limitation and energy limitation were also evident from the observation that biomass concentrations in the cultures were proportional to the concentration of ethanol in the reservoir media. Nevertheless, low concentrations of a few organic metabolites (glycolate, citrate, and mannitol) were detected in culture supernatants. From a series of chemostat cultures grown at different dilution rates, the maintenance energy requirements for ethanol and oxygen were estimated at 4.1 mmol of ethanol (middot) g of biomass(sup-1) (middot) h(sup-1) and 11.7 mmol of O(inf2) (middot) g of biomass(sup-1) (middot) h(sup-1), respectively. When biomass yields were corrected for these maintenance requirements, the Y(infmax) values on ethanol and oxygen were 13.1 g of biomass (middot) mol of ethanol(sup-1) and 5.6 g of biomass (middot) mol of O(inf2)(sup-1), respectively. These biomass yields are very low in comparison with those of other microorganisms grown under comparable conditions. To investigate whether the low growth efficiency of A. pasteurianus might be due to a low gain of metabolic energy from respiratory dissimilation, (symbl)H(sup+)/O stoichiometries were estimated during acetate oxidation by cell suspensions. These experiments indicated an (symbl)H(sup+)/O stoichiometry for acetate oxidation of 1.9 (plusmn) 0.1 mol of H(sup+)/mol of O. Theoretical calculations of growth energetics showed that this low (symbl)H(sup+)/O ratio adequately explained the low biomass yield of A. pasteurianus in ethanol-limited cultures.