Comamonas testosteroni BR6020 possesses a single genetic locus for extradiol cleavage of protocatechuate

A key intermediate for biodegradation of various distinct aromatic growth s ubstrates in Comamonas testosteroni is protocatechuate (Pca), which is meta bolized by the 4,5-extradiol (meta) ring fission pathway. A locus harbourin g genes from C. testosteroni BR6020 was cloned, dubbed pmd, which encodes t he enzymes that degrade Pca. The identity of pmdAB, encoding respectively t he alpha- and beta -subunit of the Pca ring-cleavage enzyme, was confirmed by N-terminal sequencing and molecular mass determination of both subunits from the separated enzyme. Disruption of pmdA resulted in a strain unable t o grow on Pca and a variety of aromatic substrates funnelled through this c ompound (m- and p-hydroxybenzoate, p-sulfobenzoate, phthalate, isophthalate , terephthalate, vanillate, isovanillate and veratrate). Growth on benzoate and o-aminobenzoate (anthranilate) was not affected in this strain, indica ting that these substrates are metabolized via a different lower pathway. T entative functions for the products of other pmd genes were assigned based on sequence identity and/or similarity to proteins from other proteobacteri a involved in uptake or metabolism of aromatic compounds. This study provid es evidence for a single lower pathway in C. testosteroni for metabolism of Pca, which is generated by different upper pathways acting on a variety of aromatic substrates.