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Appl Environ Microbiol. 1987 February; 53(2): 434-439
Copyright © 1987, American Society for Microbiology. All Rights Reserved.

Kinetics of Butyrate, Acetate, and Hydrogen Metabolism in a Thermophilic, Anaerobic, Butyrate-Degrading Triculture

Birgitte K. Ahring^,* and Peter Westermann

Department of General Microbiology, University of Copenhagen, Sølvgade 83 H, 1307 Copenhagen K, Denmark

ABSTRACT

Kinetics of butyrate, acetate, and hydrogen metabolism were determined with butyrate-limited, chemostat-grown tricultures of a thermophilic butyrate-utilizing bacterium together with Methanobacterium thermoautotrophicum and the TAM organism, a thermophilic acetate-utilizing methanogenic rod. Kinetic parameters were determined from progress curves fitted to the integrated form of the Michaelis-Menten equation. The apparent half-saturation constants, K_m, for butyrate, acetate, and dissolved hydrogen were 76 µM, 0.4 mM, and 8.5 µM, respectively. Butyrate and hydrogen were metabolized to a concentration of less than 1 µM, whereas acetate uptake usually ceased at a concentration of 25 to 75 µM, indicating a threshold level for acetate uptake. No significant differences in K_m values for butyrate degradation were found between chemostat- and batch-grown tricultures, although the maximum growth rate was somewhat higher in the batch cultures in which the medium was supplemented with yeast extract. Acetate utilization was found to be the rate-limiting reaction for complete degradation of butyrate to methane and carbon dioxide in continuous culture. Increasing the dilution rate resulted in a gradual accumulation of acetate. The results explain the low concentrations of butyrate and hydrogen normally found during anaerobic digestion and the observation that acetate is the first volatile fatty acid to accumulate upon a decrease in retention time or increase in organic loading of a digestor.

^* Corresponding author.

Present address: Institute of Biotechnology, The Technical University of Denmark, 2800 Lyngby, Denmark.

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