Abstract
Heavy metal co-contamination in crude oil-polluted environments may inhibit microbial bioremediation of hydrocarbons. The model heavy metal-resistant bacterium Cupriavidus metallidurans CH34 possesses cadmium and mercury resistance, as well as genes related to the catabolism of hazardous BTEX aromatic hydrocarbons. The aims of this study were to analyze the aromatic catabolic potential of C. metallidurans CH34 and to determine the functionality of the predicted benzene catabolic pathway and the influence of cadmium and mercury on benzene degradation. Three chromosome-encoded bacterial multicomponent monooxygenases (BMMs) are involved in benzene catabolic pathways. Growth assessment, intermediates identification, and gene expression analysis indicate the functionality of the benzene catabolic pathway. Strain CH34 degraded benzene via phenol and 2-hydroxymuconic semialdehyde. Transcriptional analyses revealed a transition from the expression of catechol 2,3-dioxygenase (tomB) in the early exponential phase to catechol 1,2-dioxygenase (catA1 and catA2) in the late exponential phase. The minimum inhibitory concentration to Hg (II) and Cd (II) was significantly lower in the presence of benzene, demonstrating the effect of co-contamination on bacterial growth. Notably, this study showed that C. metallidurans CH34 degraded benzene in the presence of Hg (II) or Cd (II).
Highlights
IntroductionToluene, ethylbenzene, and xylene isomers, commonly known as BTEX, are volatile monoaromatic hydrocarbons often present in crude oil spilled sites and polluted industrial areas [1,2]
The aromatic catabolism of C. metallidurans CH34 was reconstructed on the basis of its genome and using the genomic information of aromatic-degrading bacteria
We reported a wide variety of aromatic compounds that can be used as carbon source by C. metallidurans CH34, and the aromatic catabolic pathways including the routes to degrade BTEX, chlorobenzoates, and lignin-derived compounds were inferred from genomic studies
Summary
Toluene, ethylbenzene, and xylene isomers, commonly known as BTEX, are volatile monoaromatic hydrocarbons often present in crude oil spilled sites and polluted industrial areas [1,2]. These compounds can spread to distant locations from their original locations, polluting natural water bodies, groundwater, and atmospheric air [3]. BTEX are hazardous to living organisms; their toxicity, mutagenicity, and carcinogenic effects increase during bioaccumulation in animal and human tissues. Benzene is the most unsafe and toxic component of this group, causing cancer and leukemia in humans [4]
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