Genetic and Biochemical Characterization of 2-Chloro-5-Nitrophenol Degradation in a Newly Isolated Bacterium, Cupriavidus sp. Strain CNP-8.

Jun Min,Jinpei Wang,Xiaoke Hu,Weiwei Chen

doi:10.3389/fmicb.2017.01778

Abstract

Compound 2-chloro-5-nitrophenol (2C5NP) is a typical chlorinated nitroaromatic pollutant. To date, the bacteria with the ability to degrade 2C5NP are rare, and the molecular mechanism of 2C5NP degradation remains unknown. In this study, Cupriavidus sp. strain CNP-8 utilizing 2-chloro-5-nitrophenol (2C5NP) and meta-nitrophenol (MNP) via partial reductive pathways was isolated from pesticide-contaminated soil. Biodegradation kinetic analysis indicated that 2C5NP degradation by this strain was concentration dependent, with a maximum specific degradation rate of 21.2 ± 2.3 μM h−1. Transcriptional analysis showed that the mnp genes are up-regulated in both 2C5NP- and MNP-induced strain CNP-8. Two Mnp proteins were purified to homogeneity by Ni-NTA affinity chromatography. In addition to catalyzing the reduction of MNP, MnpA, a NADPH-dependent nitroreductase, also catalyzes the partial reduction of 2C5NP to 2-chloro-5-hydroxylaminophenol via 2-chloro-5-nitrosophenol, which was firstly identified as an intermediate of 2C5NP catabolism. MnpC, an aminohydroquinone dioxygenase, is likely responsible for the ring-cleavage reaction of 2C5NP degradation. Gene knockout and complementation indicated that mnpA is necessary for both 2C5NP and MNP catabolism. To our knowledge, strain CNP-8 is the second 2C5NP-utilizing bacterium, and this is the first report of the molecular mechanism of microbial 2C5NP degradation.

Highlights

Chlorinated nitroaromatic compounds (CNAs) are a group of widely distributed pollutants in the environment throughout the world due to their massive use in the manufacture of herbicides, drugs, dyes and other chemicals (Liu et al, 2011; Tiwari et al, 2017)
Cupriavidus strains were grown at 30◦C in minimal salt medium (MSM, omitting the CaCl2) (Xiao et al, 2006) with different substrates (2C5NP was dissolved in Minimal salt medium (MSM) with initial concentration of 5 mM)
Succinate was proved as the best additional carbon source during 2C5NP degradation by strain CNP-8

Summary

Introduction

Chlorinated nitroaromatic compounds (CNAs) are a group of widely distributed pollutants in the environment throughout the world due to their massive use in the manufacture of herbicides, drugs, dyes and other chemicals (Liu et al, 2011; Tiwari et al, 2017). The natural formation of CNAs is extremely rare. Most of these xenobiotics in the environment are mainly derived from their manufacture, transport and use. Chemical or biological degradation of their derivatives in the environment is another major source. Many CNAs are listed as priority pollutants by the United State Environmental Protection Agency (USEPA). Removal of these toxicants from the environment has aroused wide concern

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Conclusion