Research Article: Biodegradation of 2-chloro-4-nitrophenol via a hydroxyquinol pathway by a Gram-negative bacterium, Cupriavidus sp. strain CNP-8

Date Published: March 20, 2018

Publisher: Springer Berlin Heidelberg

Author(s): Jun Min, Jinpei Wang, Weiwei Chen, Xiaoke Hu.

http://doi.org/10.1186/s13568-018-0574-7

Abstract

Cupriavidus sp. strain CNP-8 isolated from a pesticide-contaminated soil was able to utilize 2-chloro-4-nitrophenol (2C4NP) as a sole source of carbon, nitrogen and energy, together with the release of nitrite and chloride ions. It could degrade 2C4NP at temperatures from 20 to 40 °C and at pH values from 5 to 10, and degrade 2C4NP as high as 1.6 mM. Kinetics assay showed that biodegradation of 2C4NP followed Haldane substrate inhibition model, with the maximum specific growth rate (μmax) of 0.148/h, half saturation constant (Ks) of 0.022 mM and substrate inhibition constant (Ki) of 0.72 mM. Strain CNP-8 was proposed to degrade 2C4NP with hydroxyquinol (1,2,4-benzenetriol, BT) as the ring-cleavage substrate. The 2C4NP catabolic pathway in strain CNP-8 is significant from those reported in other Gram-negative 2C4NP utilizers. Enzymatic assay indicated that the monooxygenase initiating 2C4NP catabolism had different substrates specificity compared with previously reported 2C4NP monooxygenations. Capillary assays showed that strain CNP-8 exhibited metabolism-dependent chemotactic response toward 2C4NP at the optimum concentration of 0.5 mM with a maximum chemotaxis index of 37.5. Furthermore, microcosm studies demonstrated that strain CNP-8, especially the pre-induced cells, could remove 2C4NP rapidly from the 2C4NP-contaminated soil. Considering its adaptability to pH and temperature fluctuations and great degradation efficiency against 2C4NP, strain CNP-8 could be a promising candidate for the bioremediation of 2C4NP-contaminated sites.

Partial Text

Chloronitrophenols (CNPs) are typical representatives of chlorinated nitroaromatics, which are widely utilized in synthesizing pesticides, fungicides, drugs, dyes, among others (Arora et al. 2012a, b). The natural formation of CNPs is extremely rare, and most of these xenobiotics in the environment are mainly coming from their manufacture and use, and the chemical or biological degradation of their derivatives. As the most common isomer of CNPs, 2-chloro-4-nitrophenol (2C4NP) is used for production of herbicide dicapthon and fungicide nitrofungin (Min et al. 2014). Due to its water solubility and high mobility, 2C4NP has caused serious contamination to agricultural soils and water resources, and has caused severe health effects to humans and animals (Arora et al. 2014a). Therefore, removal of 2C4NP from the environment has recently aroused wide concern.

To estimate the kinetics parameters of 2C4NP degradation, the effect of initial 2C4NP concentration (0.05–2 mM) on growth of strain CNP-8 was investigated. Cell growth kinetics was modeled by the following equation as described (Wang et al. 2010):1documentclass[12pt]{minimal}
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begin{document}$$mu = frac{{ln left( {X/X_{0} } right)}}{{t – t_{0} }}$$end{document}μ=lnX/X0t-t0where X represents the biomass (mg/L), µ represents the specific growth rate (h−1) and t represents the time.

Several pure bacterial cultures have been isolated based on their ability to degrade 2C4NP (Ghosh et al. 2010; Arora and Jain 2011; Pandey et al. 2011; Arora and Jain 2012; Tiwari et al. 2017), but strain CNP-8 reported in present study is able to tolerate and degrade higher concentrations of 2C4NP than any other 2C4NP-utilizers. Our 2C4NP-degrading isolate can utilize 2C4NP up to concentration of 1.6 mM, while 2C4NP more than 0.5 mM has been reported to completely inhibit the growth of previously reported 2C4NP-utilizers including Burkholderia sp. RKJ800 (Arora and Jain 2012) and Cupriavidus strain a3 (Tiwari et al. 2017). Moreover, strain CNP-8 can adapt to a wide range of pH from 5 to 10, whereas strain a3 was reported to be unable to degrade 2C4NP at pH lower than 6 or higher than 9 (Tiwari et al. 2017). On the other hand, strain CNP-8 is also capable to utilize 2C5NP, which is the isomer of 2C4NP and usually coexist with 2C4NP in the industrial wastewater. However, there are no documented cases of 2C5NP degradation by other 2C4NP-degrading bacteria. From a practical point of view, these combined advantages of strain CNP-8 indicated that it could be a promising candidate for bioremediation of chloronitrophenols-contaminated environment.

 

Source:

http://doi.org/10.1186/s13568-018-0574-7

 

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