Journal
APPLIED AND ENVIRONMENTAL MICROBIOLOGY
Volume 76, Issue 9, Pages 2940-2945Publisher
AMER SOC MICROBIOLOGY
DOI: 10.1128/AEM.02990-09
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- Horticulture Australia Ltd.
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A highly efficient carbendazim (methyl-1H-benzimidazol-2-ylcarbamate, or MBC)-mineralizing bacterium was isolated from enrichment cultures originating from MBC-contaminated soil samples. This bacterium, Nocardioides sp. strain SG-4G, hydrolyzed MBC to 2-aminobenzimidazole, which in turn was converted to the previously unknown metabolite 2-hydroxybenzimidazole. The initial steps of this novel metabolic pathway were confirmed by growth and enzyme assays and liquid chromatography-mass spectrometry (LC-MS) studies. The enzyme responsible for carrying out the first step was purified and subjected to N-terminal and internal peptide sequencing. The cognate gene, named mheI (for MBC-hydrolyzing enzyme), was cloned using a reverse genetics approach. The MheI enzyme was found to be a serine hydrolase of 242 amino acid residues. Its nearest known relative is an uncharacterized hypothetical protein with only 40% amino acid identity to it. Codon optimized mheI was heterologously expressed in Escherichia coli, and the His-tagged enzyme was purified and biochemically characterized. The enzyme has a K-m and k(cat) of 6.1 mu M and 170 min(-1), respectively, for MBC. Radiation-killed, freeze-dried SG-4G cells showed strong and stable MBC detoxification activity suitable for use in enzymatic bioremediation applications.
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