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Appl Environ Microbiol. 1983 May; 45(5): 1466-1473

Kinetics of Microbial Dehalogenation of Haloaromatic Substrates in Methanogenic Environments

Joseph M. Suflita, Joseph A. Robinson and James M. Tiedje

¹ Departments of Crop and Soil Sciences and of Microbiology and Public Health, ² Michigan State University, East Lansing, Michigan 48824

ABSTRACT

The kinetic parameters associated with the microbial dehalogenation of 3-chlorobenzoate, 3,5-dichlorobenzoate, and 4-amino-3,5-dichlorobenzoate were measured in anoxic sediment slurries and in an enriched methanogenic culture grown on 3-chlorobenzoate. The initial dehalogenation of the substrates exhibited Michaelis-Menten kinetics. The apparent K_m values for the above substrates ranged from 30 to 67 µM. The pattern of degradation, however, was unusual. The enrichment culture accumulated partially dehalogenated intermediates to 72 and 98% of that possible when incubated with either 3,5-dichloro- or 4-amino-3,5-dichlorobenzoate, respectively, but did not accumulate significant amounts of benzoate when 3-chlorobenzoate was the sole carbon and energy source. The accumulated intermediates were rapidly metabolized only after the parent substrate concentrations were nearly depleted (<5 µM). A sequential Michaelis-Menten model was developed to account for the observed pattern of biodegradation. Using this model, we found that relative differences in the K_m and V_max parameters for substrate and intermediate dehalogenations alone were insufficient to explain the transitory accumulation of intermediates. However, by inserting a competitive inhibition term, with the primary substrate as the inhibitor, the observed pattern of degradation was simulated. Apparently, the dichlorinated substrates competitively inhibit the dehalogenation of the monochlorinated substrates. Similar kinetic patterns were noted for sediments, although the rates were slower than in the enrichment culture.

Present address: Department of Botany and Microbiology, University of Oklahoma, Norman, OK 73019.

Present address: Department of Civil Engineering, Montana State University, Bozeman, MT 59717.

Published as journal article no. 10665 of the Michigan Agricultural Experiment Station.