Identifying and sequencing a Mycobacterium sp. strain F4 as a potential bioremediation agent for quinclorac.

Yingying Li,Yue Li,Wu Chen,Feng Luo,Lianyang Bai,Yunsheng Wang,Kun Luo,Shihui Yang

doi:10.1371/journal.pone.0185721

Yingying Li, Yue Li + Show 6 more

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https://doi.org/10.1371/journal.pone.0185721

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Abstract

Quinclorac is a widely used herbicide in rice filed. Unfortunately, quinclorac residues are phytotoxic to many crops/vegetables. The degradation of quinclorac in nature is very slow. On the other hand, degradation of quinclorac using bacteria can be an effective and efficient method to reduce its contamination. In this study, we isolated a quinclorac bioremediation bacterium strain F4 from quinclorac contaminated soils. Based on morphological characteristics and 16S rRNA gene sequence analysis, we identified strain F4 as Mycobacterium sp. We investigated the effects of temperature, pH, inoculation size and initial quinclorac concentration on growth and degrading efficiency of F4 and determined the optimal quinclorac degrading condition of F4. Under optimal degrading conditions, F4 degraded 97.38% of quinclorac from an initial concentration of 50 mg/L in seven days. Our indoor pot experiment demonstrated that the degradation products were non-phytotoxic to tobacco. After analyzing the quinclorac degradation products of F4, we proposed that F4 could employ two pathways to degrade quinclorac: one is through methylation, the other is through dechlorination. Furthermore, we reconstructed the whole genome of F4 through single molecular sequencing and de novo assembly. We identified 77 methyltransferases and eight dehalogenases in the F4 genome to support our hypothesized degradation path.

Highlights

Bioremediation using microorganisms is an important method to reduce the contamination of toxic chemical residue [1]
After culturing quinclorac contaminated soil, we isolated three bacteria strains with clear zone colonies, which had the capability to degrade quinclorac
Two degradation products by F4 were identified as quinclorac methyl ester, 3-chloro-7-hydroxyquinoline-8-carboxylic acid or 7-chloro-3-hydroxyquinoline-8-carboxylic acid

Summary

Introduction

Bioremediation using microorganisms is an important method to reduce the contamination of toxic chemical residue [1]. Due to the low dosage, longevity and especially effective control of barnyard grass and certain dicot grasses, quinclorac (3,7-dichloro-8-quinoline-carboxylic acid) is widely used in rice fields [2]. The quinclorac causes the cyanide accumulation in the tissues of susceptible plants, and eventually leads to their death [2,3]. The quinclorac residues are phytotoxic to many crops and vegetables. In fields of rice-economic crops and vegetables rotation, the phytotoxicity of quinclorac can significantly reduce the yield and quality of economic crops and vegetables, such as rice and tobacco [4].

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