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Chlorothalonil (2, 4, 5, 6-tetrachloroisophthalonitrile, TPN) has been widely used as a wide-spectrum fungicide in China and other countries, and is considered to be an important soil and water contaminant. Here we report the isolation and characterization of a novel TPN-degrading bacterial strain TP-D1 from a heavily TPN-polluted soil in Henan Province, China, and identified it as a strain of Ochrobactrum lupini based on 16S rRNA gene sequence analysis and its morphological, biochemical, and physiological characteristics. Strain TP-D1 could degrade 90.4 and 99.7% of TPN after 4- and 7-day incubation in mineral salt broth with 50 mg TPN l and in autoclaved soil with 50 μg TPN g, respectively. Two new metabolites, methyl 2, 5, 6-trichloro-3-cyano-4-methoxy-benzoate (metabolite C) and methyl 3-cyano-2, 4, 5, 6-tetrachlorobenzoate (metabolite D), were detected besides previously reported 4-hydroxy-2, 5, 6-trichloroisophthalonitrile (TPN-OH, metabolite A). This result suggests that the cyano-group in TPN could be converted into amide groups by strain TP-D1, and reveal the biodegradation mechanism of TPN in soil. [ABSTRACT FROM AUTHOR]