The presence of herbicides residues in soil represents a serious problem for agriculture. Quinclorac is a common herbicide applied in rice field, but its residue can cause abnormal growth in successive crop of tobacco in Southern China. Remediation by microorganisms is considered to be an environmentally friendly method to remove such pollutants injury. The aims of this study were to obtain quinclorac remediation isolates and to investigate the possible mechanism(s) of remediation. Six bacterial isolates were obtained from rhizosphere of rice-tobacco rotation fields, and were found to be capable of degrading quinclorac on a mineral salt medium (MSM), with degradation efficiency ranging from 2.1 to 23.7%. Among these isolates, J5 had the highest degradation efficiency, and was identified as Klebsiella variicola based on phylogenetic analyses and a metabolic profile generating by Biolog GEN III system. Bioremediation of quinclorac injury was confirmed using pot assays with tobacco, in which J5 reversed the detrimental effect of quinclorac on leaf area, leaf number, and plant height. The J5 isolate also seemed to promote plant growth, in terms of tobacco seedling growth and seed germination, which were 2.2 times and 1.6 times higher compared to untreated control, respectively. The mechanisms of plant growth promoting (PGP) traits were found to involve nitrogen-fixing, indole-3-acetic acid (IAA) production, and phosphate solubilization ability. In addition, proteomic analysis and relative quantitative PCR revealed an elevated level of 4-hydroxyphenylacetate 3-monooxygenase (HPMO) in quinclorac-treated J5, suggesting that this enzyme may play an important role in quinclorac remediation. This study showed that the J5 isolate could be exploited to not only assist in soil remediation due to quinclorac residue issues but also promote tobacco growth.
Keywords: Bioremediation; Herbicide; Klebsiella variicola; Plant growth-promoting bacterium; Tobacco.
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