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Genetics and Molecular Biology |
Institute of Biology, College of Natural Sciences, Carleton University, Ottawa, Ontario, CanadaK1S 5B61
Faculty of Biology, The University, D-78457, Konstanz, Germany2
Author for correspondence: R. Campbell Wyndham. Tel: +1 613 520 2600 ext. 3651. Fax: +1 613 520 3539. e-mail: cwyndham{at}ccs.carleton.ca
A key intermediate for biodegradation of various distinct aromatic growth substrates in Comamonas testosteroni is protocatechuate (Pca), which is metabolized by the 4,5-extradiol (meta) ring fission pathway. A locus harbouring genes from C. testosteroni BR6020 was cloned, dubbed pmd, which encodes the enzymes that degrade Pca. The identity of pmdAB, encoding respectively the 
- and ß-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 to grow on Pca and a variety of aromatic substrates funnelled through this compound (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, indicating that these substrates are metabolized via a different lower pathway. Tentative functions for the products of other pmd genes were assigned based on sequence identity and/or similarity to proteins from other proteobacteria involved in uptake or metabolism of aromatic compounds. This study provides 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.
Keywords: aromatic, biodegradation, meta ring fission, lig genes
Abbreviations: Ap, ampicillin; Cm, chloramphenicol; HCMS, 2-hydroxy-4-carboxymuconate semialdehyde; HCMSD, HCMS dehydrogenase; Km, kanamycin; MMA, minimal medium A; OCA, 4-oxalocitramalate aldolase; Pca, protocatechuate; PDCH, 2-pyrone-4,6-dicarboxylic acid hydrolase; PMD, Pca 4,5-dioxygenase
The GenBank accession number for the sequence reported in this paper is AF305325.
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