Biodegradation of S-Triazine Herbicides Under Saline Conditions by Paenarthrobacter ureafaciens PC, a New Halotolerant Bacterial Isolate: Insights into Both the Degradative Pathway and Mechanisms of Tolerance to High Salt Concentrations.

Abstract

In this study, a halotolerant bacterial strain was isolated and identified. This bacterium was confirmed to efficiently degrade s-triazine herbicides under saline conditions. The optimal conditions for the metabolism and growth of this strain were determined through single-factor tests. Furthermore, the biodegradation pathways of prometryne (the target compound) by this strain were proposed based on the detection of possible degradation intermediates and genome sequencing analysis. Additionally, a possible halotolerance mechanisms of this strain were also revealed through screening halotolerance-related genes in its genome. The results demonstrated that a halotolerant bacterial strain (designated PC), which completely degraded 20.00 mg/L prometryne within 12 h under saline conditions (30.0 g/L NaCl), was isolated and identified as Paenarthrobacter ureafaciens. The optimal conditions for the metabolism and growth of the strain PC were identified as follows: yeast extract as the additional carbon source with the concentration of ≥0.1 g/L, NaCl concentration of ≤30.0 g/L, initial pH of 7.0, temperature of 35.0 °C, and shaking speed of ≥160 rpm. Furthermore, the strain PC demonstrated efficient removal of other s-triazine herbicides, including atrazine, ametryne, simetryne, and cyanazine. The strain PC might degrade prometryne through a series of steps, including demethylthiolation, deisopropylamination, deamination, dealkalation, decarboxylation, etc., relying on the relevant functional genes involved in the degradation of s-triazine compounds. Furthermore, the strain PC might tolerate high salinity through the excessive uptake of K⁺ into cells, intracellular accumulation of compatible solutes, and production of halophilic enzymes. This study is expected to provide a potentially effective halotolerant bacterium for purifying s-triazine pollutants in saline environments.