pWW174: A large plasmid from Acinetobacter calcoaceticus encoding benzene catabolism by the β‐ketoadipate pathway

Abstract

Acinetobacter calcoaceticus RJE74 contains a large transmissible catabolic plasmid, pWW174, of about 200 kb, which encodes its ability to grow on benzene (Bzn+). pWW174 was unstable in Acinetobacter hosts and was lost at high frequency in the absence of selection for Bzn+. The catabolic pathway appeared to be via benzene cis-glycol, catechol and the beta-ketoadipate (ortho) pathway. pWW174 encodes a catechol 1,2-oxygenase which is significantly more thermolabile than the chromosomally determined enzyme. pWW174 was able to complement all cat mutants (catechol to central metabolites) of A. calcoaceticus ADP1 (BD413) tested. Two regions of the plasmid were cloned, one carrying catA, the gene for catechol 1,2-oxygenase, and another carrying catBCDE, the subsequent four enzymes of the beta-ketoadipate pathway: these two regions appeared to be separated by at least 10 kbp. Hybridization indicated homology between the plasmid cat genes and the corresponding chromosomal genes of ADP1.

The biodegradation of aromatic hydrocarbons by bacteria

“…Although there have been recent reports of the isolation of new bacterial strains which can grow on benzene (Shirai 1986;van den Tweel et al 1988;Winstanley et al 1987, as examples) the biodegradation routes were, not surprisingly, the same as those outlined above (Fig. 1).…”

“…1). Winstanley et al (1987) described a new benzene utilising bacterium, Acinectobacter calcoaceticus RJE74, which carries a large plasmid (pWW174) encoding the enzymes for the catabolism of benzene via the ~-ketoadipate pathway (that involving catechol 1,2-dioxygenase). This was the first report of the ortho pathway being plasmid encoded and was one of very few citations of plasmids in this genus.…”

Characterization of Acinetobacter calcoaceticus catM, a repressor gene homologous in sequence to transcriptional activator genes

“…Genes for enzymes mediating consecutive catabolic reactions are frequently clustered within operons on Pseudomonas plasmids, and transcription of the operons tends to be under positive control exerted by the products of activator genes (10,34). Although catabolic genes have also been located on plasmids associated with Acinetobacter calcoacticus strains (47), little is known about the regulation of either plasmid or chromosomal genes in this genus.…”

The fluorene catabolic linear plasmid in Terrabacter sp. strain DBF63 carries the β-ketoadipate pathway genes, pcaRHGBDCFIJ, also found in proteobacteria

“…The bketoadipate pathway is widely distributed among diverse soil microbes, and plays an important role in the metabolism of naturally occurring aromatic compounds and environmental pollutants. The pathway genes are usually located chromosomally in proteobacteria (Harwood & Parales, 1996), although there are some exceptions such as pWW174 from Acinetobacter calcoaceticus (Winstanley et al, 1987) and pSymB from Sinorhizobium meliloti (Finan et al, 2001). Similarly, in actinobacteria the pca genes are not located on plasmids.…”