4-Chlorobenzoate Metabolism by Acinetobacter SP. 4-CB 1 and Its Relevance to Biodegradation of 4,4′-Dichlorobiphenyl

Abstract

A microorganism was isolated from a PCB-contaminated soil by liquid culture enrichment on 4-chlorobenzoate (4-CB) as a sole source of carbon and energy. It was identified as an Acinetobacter sp. The pure culture was able to grow on benzoate, 4-hydroxybenzoate, 3-hydroxybenzoate, and mixtures of 3-chlorobenzoate + 3-hydroxybenzoate and 2-chlorobenzoate + 2-hydroxybenzoate. No growth was observed on 2-hydroxybenzoate, 2-chlorobenzoate, and 3-chlorobenzoate as the sole carbon and energy sources. Oxygen uptake measurements with resting cells, grown on benzoate or 4-chlorobenzoate, yielded low oxygen uptake rates with 4-hydroxybenzoate or protocatechuate, as compared to uptake rates of 4-hydroxybenzoate-grown cells (about 10%). This indicates that 4-CB degradation does not follow the protocatechuate pathway and that dechlorination of the aromatic ring is unlikely. The rate of oxygen uptake of resting cells grown on 4-CB was in the following order: 4-chlorobenzoate > 2-chlorobenzoate > 3-chlorobenzoate. Aerobic assays with cells grown on each of the previously mentioned substrates were performed over an incubation period of four hours to check substrate disappearance and chloride release. Acinetobacter P6 (Furukawa et al., 1979) was incubated with 0.5 mM 4,4′-dichlorobiphenyl (4,4′-DCB) and 2.0 mM biphenyl in liquid culture alone and in co-culture with Acinetobacter sp. 4-CB 1. Whereas 4-CB accumulated in the monoculture, no 4-CB was found in the co-culture.