para-Nitrophenol 4-monooxygenase and hydroxyquinol 1,2-dioxygenase catalyze sequential transformation of 4-nitrocatechol in Pseudomonas sp. strain WBC-3
Pseudomonas sp. strain WBC-3 utilizes para-nitrophenol (PNP) as a sole source of carbon, nitrogen and energy. PnpA (PNP 4-monooxygenase) and PnpB (para-benzoquinone reductase) were shown to be involved in the initial steps of PNP catabolism via hydroquinone. We demonstrated here that PnpA also catalyzed monooxygenation of 4-nitrocatechol (4-NC) to hydroxyquinol, probably via hydroxyquinone. It was the first time that a single-component PNP monooxygenase has been shown to catalyze this conversion. PnpG encoded by a gene located in the PNP degradation cluster was purified as a His-tagged protein and identified as a hydroxyquinol dioxygenase catalyzing a ring-cleavage reaction of hydroxyquinol. Although all the genes necessary for 4-NC metabolism seemed to be present in the PNP degradation cluster in strain WBC-3, it was unable to grow on 4-NC as a sole source of carbon, nitrogen and energy. This was apparently due to the substrate’s inability to trigger the expression of genes involved in degradation. Nevertheless, strain WBC-3 could completely degrade both PNP and 4-NC when PNP was used as the inducer, demonstrating its potential in bioremediation of the environment polluted by both 4-NC and PNP.
Keywords4-Nitrocatechol Hydroxyquinol 1,2-dioxygenase para-Nitrophenol 4-monooxygenase Pseudomonas Transformation
We acknowledge financial supports from the National High Technology Research and Development Program of China (2006AA10Z403) and National Natural Science Foundation of China (30570021).
- Moonen MJ, Synowsky SA, van den Berg WA, Westphal AH, Heck AJ, van den Heuvel RH, Fraaije MW, van Berkel WJ (2008) Hydroquinone dioxygenase from Pseudomonas fluorescens ACB: a novel member of the family of nonheme-iron(II)-dependent dioxygenases. J Bacteriol 190(15):5199–5209CrossRefPubMedGoogle Scholar
- Takeo M, Murakami M, Niihara S, Yamamoto K, Nishimura M, Kato D, Negoro S (2008) Mechanism of 4-nitrophenol oxidation in Rhodococcus sp. Strain PN1: characterization of the two-component 4-nitrophenol hydroxylase and regulation of its expression. J Bacteriol 190(22):7367–7374CrossRefPubMedGoogle Scholar