Paraquat is an herbicide widely used to control weeds in various crops. Due to its use in large quantities, its dispersal into the environment is frequent, leading to contamination and negative health effects on non-target organisms because of its high toxicity and persistence in soils. Therefore, it is necessary to develop sustainable strategies to remediate sites contaminated by this compound. Bacterial remediation is a promising alternative for removing paraquat from the environment; however, the metabolic pathways used by bacteria for its degradation have not yet been precisely described. In this context, it is essential to characterize bacterial species capable of resisting and degrading paraquat, as well as to elucidate the molecular mechanisms involved in these processes. The objective of this work was to evaluate the paraquat resistance and degradation potential of the bacterial strain Caballeronia zhejiangensis CEIB S4-3, and to identify genes with a possible role in the resistance and degradation of this herbicide by analyzing the strain’s genome. The results of this research showed that, in solid medium, C. zhejiangensis CEIB S4-3 can withstand concentrations of up to 200 mg/L of paraquat supplemented as a commercial formulation (Gramoxone®) and 400 mg/L of analytical-grade paraquat. In tryptic soy broth, the strain grew in the presence of both the commercial formulation and analytical-grade paraquat at concentrations up to 15 mg/L, whereas in mineral salts medium, supplemented with paraquat or its commercial formulation as the sole nutrient source, the strain survived exposure to paraquat at the same concentrations. Furthermore, the bacterial strain removed 40.8% of the paraquat supplemented in the culture medium at a concentration of 12 mg/L within 48 h. Finally, genomic analysis revealed the presence of genes related to paraquat resistance mechanisms and encoding enzymes involved in the degradation of this herbicide. These results position C. zhejiangensis CEIB S4-3 as a promising candidate for developing remediation alternatives for sites contaminated with this herbicide.
Morales-Olivares et al. (Fri,) studied this question.