Degradation of 3-chlorobenzoate by benzoate or 3-methylbenzoate-utilising cultures: 3-chlorobenzoate; mixed cultures; total degradation; incompatible substrates

Abstract

3-Chlorobenzoate (3CB) was incompletely degraded by bacterial cultures growing continuously with benzoate (Ben) or 3-methylbenzoate (3MB). Accumulation of chlorocatechols as dead-end metabolites was avoided if, prior to the exposure to 3CB, the population had been supplemented with Pseudomonas sp. strain B13 as a chlorocatechol-assimilating member. After acclimatisation, the substrate mixture Ben/3CB was completely degraded via 2 compatible ortho-cleavage pathways. In contrast, 3MB and 3CB were found to be incompatible substrates: as a result of suicide and genetic inactivation of catechol 2,3-dioxygenase, methylcatechols are subject to unproductive ortho-cleavage. In a defined mixed culture ( Pseudomonas putida mt-2 plus strain B13), 4-carboxymethyl-2-methylbut-2-en-4-olide and 4-carboxymethyl-4-methylbut-2-en-4-olide were excreted as dead-end products, whereas in an undefined mixed culture, degraders of these metabolites became stable members of the community. Characteristically, with increasing 3CB load, the relative number of 3CB-degrading organisms increased which were Ben + or 3MB + and which had acquired from Pseudomonas sp. strain B13 the ability to assimilate chlorocatechols.