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Dissipation, dehalogenation, and denitration of chloroaromatic compounds by Nocardioides sp. strain PD653: Characterization of the substrate specificity.

ABSTRACT: The substrate range of Nocardioides sp. strain PD653, capable of mineralizing hexachlorobenzene, was investigated based on the dissipation of substrates and the liberation of halogen ions. Strain PD653 dehalogenated 10 out of 18 halophenol congeners; however, it could dehalogenate only hexachlorobenzene out of seven halobenzene congeners tested. Moreover, dehalogenation activities were shown for chloronitrobenzenes, along with an increase in the number of substituted chlorine atoms except for 2,3,4,5-tetrachloro-1-nitrobenzene. These results suggested that this strain might be applicable to remediate soil contaminated with these persistent chloroaromatic compounds.

SUBMITTER: Ito K

PROVIDER: S-EPMC6718357 | biostudies-literature | 2019 Aug

REPOSITORIES: biostudies-literature

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Dissipation, dehalogenation, and denitration of chloroaromatic compounds by <i>Nocardioides</i> sp. strain PD653: Characterization of the substrate specificity.

Ito Koji K Takagi Kazuhiro K Kataoka Ryota R Kiyota Hiromasa H Iwasaki Akio A

Journal of pesticide science 20190801 3

The substrate range of <i>Nocardioides</i> sp. strain PD653, capable of mineralizing hexachlorobenzene, was investigated based on the dissipation of substrates and the liberation of halogen ions. Strain PD653 dehalogenated 10 out of 18 halophenol congeners; however, it could dehalogenate only hexachlorobenzene out of seven halobenzene congeners tested. Moreover, dehalogenation activities were shown for chloronitrobenzenes, along with an increase in the number of substituted chlorine atoms except ...[more]

PMID: 31530974

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Project description:Enzymes that are capable of detoxifying halogenated phenols (HPs) and nitrophenols (NPs) are valuable for bioremediation and waste biorefining. HadA monooxygenase was found to perform dual functions of oxidative dehalogenation (hydroxylation plus halide elimination) and denitration (hydroxylation plus nitro elimination). Rate constants associated with individual steps of HadA reactions with phenol, halogenated phenols and nitrophenols were measured using combined transient kinetic approaches of stopped-flow absorbance/fluorescence and rapid-quench flow techniques. Density functional theory was used to calculate the thermodynamic and electronic parameters associated with hydroxylation and group elimination steps. These parameters were correlated with the rate constants of hydroxylation, group elimination, and overall product formation to identify factors controlling individual steps. The results indicated that the hydroxylation rate constant is higher when the pK a of the phenolic group is lower, i.e. it is more easily deprotonated, but not higher when the energy gap between the E LUMO of the C4a-hydroperoxy-FAD intermediate and the E HOMO of the phenolate substrate is lower. These data suggest that the substrate deprotonation has a higher energy barrier than the -OH transfer, and thus controls the hydroxylation step. For the group elimination, the process is controlled by the ability of the C-X bond to break. For the overall product formation (hydroxylation and group elimination combined), this analysis showed that the rate constant of product formation is dependent on the pK a value of the substrate, indicating that the overall reaction is controlled by substrate deprotonation. This step also likely has the highest energy barrier and thus controls the overall process of oxidative dehalogenation and denitration by HadA. This report is the first to identify a key mechanistic factor controlling the enzymatic processes of oxidative dehalogenation and denitration.

Dataset Information

Dissipation, dehalogenation, and denitration of chloroaromatic compounds by Nocardioides sp. strain PD653: Characterization of the substrate specificity.

Publications

Dissipation, dehalogenation, and denitration of chloroaromatic compounds by <i>Nocardioides</i> sp. strain PD653: Characterization of the substrate specificity.

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