2,3-Dihydroxybenzoate meta-Cleavage Pathway is Involved in o-Phthalate Utilization in Pseudomonas sp. strain PTH10

Pseudomonas sp. strain PTH10 can utilize o -phthalate which is a key intermediate in the bacterial degradation of some polycyclic aromatic hydrocarbons. In this strain, o -phthalate is degraded to 2,3-dihydroxybenzoate and further metabolized via the 2,3-dihydroxybenzoate meta -cleavage pathway. Here, the opa genes which are involved in the o -phthalate catabolism were identified. Based on the enzymatic activity of the opa gene products, opaAaAbAcAd , opaB , opaC , and opaD were found to code for o -phthalate 2,3-dioxygenase, dihydrodiol dehydrogenase, 2,3-dihydroxybenzoate 3,4-dioxygenase, and 3-carboxy-2-hydroxymuconate-6-semialdehyde decarboxylase, respectively. Collectively, these enzymes are thought to catalyze the conversion of o -phthalate to 2-hydroxymuconate-6-semialdehyde. Deletion mutants of the above opa genes indicated that their products were required for the utilization of o -phthalate. Transcriptional analysis showed that the opa genes were organized in the same transcriptional unit. Quantitative analysis of opaAa , opaB , opaC , opaD , opaE , and opaN revealed that, except for opaB and opaC , all other genes were transcriptionally induced during growth on o -phthalate. The constitutive expression of opaB and opaC , and the transcriptional induction of opaD located downstream of opaB , suggest several possible internal promoters are existence in the opa cluster. Together, these results strongly suggest that the opa genes are involved in a novel o -phthalate catabolic pathway in strain PTH10.