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Open Access Highly Accessed Research article

Identification of the para-nitrophenol catabolic pathway, and characterization of three enzymes involved in the hydroquinone pathway, in pseudomonas sp. 1-7

Shuangyu Zhang, Wen Sun, Li Xu, Xiaomei Zheng, Xiaoyu Chu, Jian Tian, Ningfeng Wu* and Yunliu Fan

Author Affiliations

Biotechnology Research Institute, Chinese Academy of Agricultural Sciences, 12 Zhongguancun South Street, Haidian District, Beijing 100081, PR China

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BMC Microbiology 2012, 12:27  doi:10.1186/1471-2180-12-27

Published: 2 March 2012

Abstract

Background

para-Nitrophenol (PNP), a priority environmental pollutant, is hazardous to humans and animals. However, the information relating to the PNP degradation pathways and their enzymes remain limited.

Results

Pseudomonas sp.1-7 was isolated from methyl parathion (MP)-polluted activated sludge and was shown to degrade PNP. Two different intermediates, hydroquinone (HQ) and 4-nitrocatechol (4-NC) were detected in the catabolism of PNP. This indicated that Pseudomonas sp.1-7 degraded PNP by two different pathways, namely the HQ pathway, and the hydroxyquinol (BT) pathway (also referred to as the 4-NC pathway). A gene cluster (pdcEDGFCBA) was identified in a 10.6 kb DNA fragment of a fosmid library, which cluster encoded the following enzymes involved in PNP degradation: PNP 4-monooxygenase (PdcA), p-benzoquinone (BQ) reductase (PdcB), hydroxyquinol (BT) 1,2-dioxygenase (PdcC), maleylacetate (MA) reductase (PdcF), 4-hydroxymuconic semialdehyde (4-HS) dehydrogenase (PdcG), and hydroquinone (HQ) 1,2-dioxygenase (PdcDE). Four genes (pdcDEFG) were expressed in E. coli and the purified pdcDE, pdcG and pdcF gene products were shown to convert HQ to 4-HS, 4-HS to MA and MA to β-ketoadipate respectively by in vitro activity assays.

Conclusions

The cloning, sequencing, and characterization of these genes along with the functional PNP degradation studies identified 4-NC, HQ, 4-HS, and MA as intermediates in the degradation pathway of PNP by Pseudomonas sp.1-7. This is the first conclusive report for both 4-NC and HQ- mediated degradation of PNP by one microorganism.

Keywords:
para-Nitrophenol; Catabolism; Hydroquinone pathway; Hydroxyquinol pathway; Pseudomonas