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With a new enrichment protocol, pentachlorophenol (PCP)-degrading bacteria were isolated from soil, water, and sewage. When characterized, all isolates were related and shared characteristics of the genus Arthrobacter. Growth rates for strain NC were determined for a number of substrates, including PCP and 2,4,6-trichlorophenol. Changes in PCP concentration affected growth rate and length of the lag phase but not cell yield. Increasing the pH from 6.8 to 7.8 decreased the length of the lag phase for growth on PCP. Cessation of growth, upon incremental addition of PCP, was found to be related to a decrease in pH rather than to a buildup of a toxic metabolite. Degradation of PCP by strain NC was shown to be complete.

The growth of a pseudomonad on 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4-DCP (2,4-dichlorophenol) was studied in batch and continuous culture. The optimum growth rate using 2,4-D was 0.14/h at 25 C in a pH range from 6.2 to 6.9. Highest specific growth rate using 2,4-DCP was 0.12/h at 25 C in a pH range from 7.1 to 7.8. Growth was strongly inhibited by 2,4-DCP above a concentration of 25 mg/liter whereas no appreciable inhibition was observed with 2,4-D at concentrations up to 2,000 mg per liter. Growth on 2,4-DCP was described by Monod kinetics at subinhibitory concentrations but the inhibition by 2,4-DCP exhibited an unusual linear response to substrate concentration, and did not fit a model based on noncompetitive inhibition. The lag phase of batch cultures was found to depend on both 2,4-DCP concentration and prior adaptation of the inoculum. A study such as this on the kinetics of growth on related substrates may be useful as a method of finding the rate-limiting step in a metabolic sequence.

The degradation of p-nitrobenzoate (p-NBA) by domestic sewage was inhibited by benzoate, and a model for this behavior was found in a soil isolate. The isolate, a pseudomonad, utilized p-NBA and benzoate by separate adaptive enzyme pathways. In oxygen uptake experiments, the degradation of p-NBA was competitively inhibited by benzoate, but the degradation of benzoate was not affected by the presence of p-NBA. 4-Nitrocatechol was not implicated in the inhibition. p-Hydroxybenzoate, which is the p-NBA degradation pathway, also had a decreased rate od degradation when benzoate was present. The growth rate of the isolate on the aromatic substrates and on glucose autoclaved in the medium was 0.3 h-1. When glucose was autoclaved separately, the growth rate was less, about 0.2 h-1. The apparent Km in oxygen uptake experiments was 25 micrometer for p-NBA and benzoate and 5 micrometer for p-hydroxybenzoate.