Isolation, Screening, and Degradation Characteristics of a Quinclorac-Degrading Bacterium, Strain D, and Its Potential for Bioremediation of Rice Fields Polluted by Quinclorac

Quinclorac (QNC) is a persistent, highly selective, hormonal herbicide of low toxicity. QNC accumulates in soil and affects the growth and development of crops planted subsequent to its application. In this study, we isolated and screened a QNC-degrading bacterial strain, strain D, from rice paddy soil. Morphological analysis, physiological and biochemical tests, and 16S rRNA gene sequencing led us to identify strain D as a Cellulosimicrobium cellulans strain. We investigated the characteristics of strain D in relation to QNC degradation. Under optimal culture conditions, the QNC degradation rate was 45.9% after 21 days of culture. QNC degradation by strain D in the field was modeled and quantified by a pot experiment. The results show that strain D promotes rice growth and degrades QNC. This research has identified a new bacterial species that degrades QNC, providing a foundation for further research into QNC remediation. IMPORTANCE QNC-degrading bacteria have been isolated from different environments, but there are no reports of Cellulosimicrobium cellulans strains that degrade QNC. In this study, a previously unidentified bacterial strain that degrades QNC, strain D, was screened from paddy soil. The characteristics of strain D that relate to QNC degradation were investigated in detail. The results showed that strain D effectively degraded QNC. Two degradation products of QNC formed by strain D that have not been reported previously, i.e., 3-pyridylacetic acid (m/z 138.0548) and 3-ethylpyridine (m/z 108.0805), were identified using high-performance liquid chromatography–quadrupole time of flight mass spectrometry. Strain D has the capacity to degrade QNC in a QNC-polluted paddy.