Degradation of three monochlorobenzoate isomers by different bacteria isolated from a contaminated soil

Three monochlorobenzoate isomer-utilizing bacterial strains, Pseudomonas sp. 2-CBA, Pseudomonas sp. 3-CBA, and Hydrogenophaga sp. 4-CBA, were isolated from a haloaromatic-contaminated soil in a disused chemical factory in Nanjing, China. Compared to strain 3-CBA and strain 4-CBA, which could only utilize its corresponding monochlorobenzoate isomer (3-chlorobenzoate and 4-chlorobenzoate) as the sole carbon source for growth, strain 2-CBA could utilize both 2-chlorobenzoate and 3-chlorobenzoate for growth. The three monochlorobenzoate isomers were catabolized via three different dechlorination pathways in the three isolates, respectively. 3-Chlorobenzoate was initially catabolized by the benzoate 1,2-dioxygenase (BenABCD) in strain 3-CBA, whereas 2-chlorobenzoate was catabolized by the hybrid 2-halobenzoate 1,2-dioxygenase system in strain 2-CBA, which comprised of the terminal oxygenase component of 2-halobenzoate dioxygenase system (CbdAB) and the reductase component of benzoate 1,2-dioxygenase system (BenC). For 4-chlorobenzoate, it was catabolized via the classic hydrolytic dehalogenation pathway in strain 4-CBA. While, strain 4-CBA seemed to have a more compact gene cluster of fcbABC compared to previously reported strains. This study provides new insights into the catabolic diversity of structurally similar isomers in a contaminated niche.