Pendimethalin Nitroreductase Is Responsible for the Initial Pendimethalin Degradation Step in Bacillus subtilis Y3.
Pendimethalin [N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine] is a selective preemergence dinitroaniline herbicide. Several fungi and bacteria have been reported to degrade pendimethalin, but the enzymes or genes involved in this process have not been characterized. Nitroreduction is the initial degradation and detoxification step for pendimethalin. In this study, a pendimethalin nitroreductase (PNR), responsible for the nitroreduction of pendimethalin, was purified from the pendimethalin-degrading strain Bacillus subtilis Y3. Based on a comparison of its mass fingerprints with all of the deduced proteins from the draft genome of strain Y3, a protein annotated as a nitroreductase was identified, and its corresponding encoding gene was termed pnr PNR was a functional homodimer with a subunit molecular mass of approximately 23 kDa. PNR reduced the C-6 nitro group of the aromatic ring of pendimethalin, yielding 2-nitro-6-amino-N-(1-ethylpropyl)-3,4-xylidine. PNR could also catalyze the nitroreduction of three other major varieties of dinitroaniline herbicides, including butralin, oryzalin, and trifluralin. However, the number of reduced nitro groups was two instead of one, which differed from the nitroreduction of pendimethalin by PNR and which may be due to the symmetry in the chemical structures of the two nitro groups. A detoxification assay revealed that 2-nitro-6-amino-N-(1-ethylpropyl)-3,4-xylidine (PNR-reduced pendimethalin) showed no inhibitory effect on the growth of Saccharomyces cerevisiae BY4741, whereas pendimethalin showed an obvious inhibitory effect on its growth, indicating the detoxification effect of pendimethalin by PNR. Therefore, PNR has potential in pendimethalin detoxification applications. This report describes an enzyme (and corresponding gene) involved in the biodegradation of pendimethalin and dinitroaniline herbicides.



Pendimethalin [N-(1-ethylpropyl)-2,6-dinitro-3,4-xylidine] is a widely used selective preemergence dinitroaniline herbicide, and its residue has been frequently detected in the environment. The U.S. Environmental Protection Agency (EPA) has classified pendimethalin as a persistent bioaccumulative toxin. To date, no enzymes or genes involved in pendimethalin biodegradation have been reported. In the present study, the gene pnr, which encodes the nitroreductase PNR, responsible for the nitroreduction of pendimethalin, was cloned from the pendimethalin-degrading strain Bacillus subtilis Y3. PNR could also catalyze the nitroreduction of three other major varieties of dinitroaniline herbicides, including butralin, oryzalin, and trifluralin. The reduction of pendimethalin by PNR might eliminate its toxicity against Saccharomyces cerevisiae BY4741, indicating the application potential of PNR in the detoxification of pendimethalin.
Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, People's Republic of China.
Hai-Yan
HY
Ni
Jiangxi Engineering Laboratory for the Development and Utilization of Agricultural Microbial Resources, College of Bioscience and Bioengineering, Jiangxi Agricultural University, Nanchang, Jiangxi, People's Republic of China.
Fei
F
Wang
Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, People's Republic of China.
Na
N
Li
Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, People's Republic of China.|Department of Biological Sciences, College of Ocean and Biology Engineering, Yancheng Teachers University, Yancheng, Jiangsu, People's Republic of China.
Li
L
Yao
Laboratory Center of Life Sciences, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, People's Republic of China.
Chen
C
Dai
Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, People's Republic of China.
Qin
Q
He
Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, People's Republic of China.|Laboratory Center of Life Sciences, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, People's Republic of China.
Jian
J
He
Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu, People's Republic of China hongqing@njau.edu.cn.
Qing
Q
Hong
D000814:Aniline Compounds / Q000737:chemistry / Q000378:metabolism*; D001412:Bacillus subtilis / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001673:Biodegradation, Environmental; D006540:Herbicides / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D015394:Molecular Structure; D009601:Nitroreductases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny
D000814:Aniline Compounds; D001426:Bacterial Proteins; D006540:Herbicides; D009601:Nitroreductases; C030856:pendimethalin
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