Biodegradation of ortho-Cresol by a Mixed Culture of Nitrate-Reducing Bacteria Growing On Toluene

John Flyvbjerg, Claus Jørgensen, Erik Arvin, Bjørn K. Jensen, Susan K. Olsen

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    A mixed culture of nitrate-reducing bacteria degraded o-cresol in the presence of toluene as a primary growth substrate. No degradation of o-cresol was observed in the absence of toluene or when the culture grew on p-cresol and 2,4-dimethylphenol. In batch cultures, the degradation of o-cresol started after toluene was degraded to below 0.5 to 1.0 mg/liter but continued only for about 3 to 5 days after the depletion of toluene since the culture had a limited capacity for o-cresol degradation once toluene was depleted. The total amount of o-cresol degraded was proportional to the amount of toluene metabolized, with an average yield of 0.47 mg of o-cresol degraded per mg of toluene metabolized. Experiments with (ring-U-14C)o-cresol indicated that about 73% of the carbon from degraded o-cresol was mineralized to CO-2 and about 23% was assimilated into biomass after the transient accumulation of unidentified water-soluble intermediates. A mathematical model based on a simplified Monod equation is used to describe the kinetics of o-cresol degradation. In this model, the biomass activity toward o-cresol is assumed to decay according to first-order kinetics once toluene is depleted. On the basis of nonlinear regression of the data, the maximum specific rate of o-cresol degradation was estimated to be 0.4 mg of o-cresol per mg of biomass protein per h, and the first-order decay constants for o-cresol-degrading biomass activity was estimated to be 0.15 h-1. We hypothesize that the mixed culture degrades o-cresol by a cometabolic mechanism in which the enzymes necessary for the degradation of o-cresol are induced by toluene and not by o-cresol.
    Original languageEnglish
    JournalApplied and Environmental Microbiology
    Issue number7
    Pages (from-to)2286-2292
    Publication statusPublished - 1993


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