Isolation and characterization of carbendazim-degrading Rhodococcus erythropolis djl-11.

Carbendazim (methyl 1H-benzimidazol-2-yl carbamate) is one of the most widely used fungicides in agriculture worldwide, but has been reported to have adverse effects on animal health and ecosystem function. A highly efficient carbendazim-degrading bacterium (strain dj1-11) was isolated from carbendazim-contaminated soil samples via enrichment culture. Strain dj1-11 was identified as Rhodococcus erythropolis based on morphological, physiological and biochemical characters, including sequence analysis of the 16S rRNA gene. In vitro degradation of carbendazim (1000 mg·L(-1)) by dj1-11 in minimal salts medium (MSM) was highly efficient, and with an average degradation rate of 333.33 mg·L(-1)·d(-1) at 28°C. The optimal temperature range for carbendazim degradation by dj1-11 in MSM was 25-30°C. Whilst strain dj1-11 was capable of metabolizing cabendazim as the sole source of carbon and nitrogen, degradation was significantly (P<0.05) increased by addition of 12.5 mM NH4NO3. Changes in MSM pH (4-9), substitution of NH4NO3 with organic substrates as N and C sources or replacing Mg(2+) with Mn(2+), Zn(2+) or Fe(2+) did not significantly affect carbendazim degradation by dj1-11. During the degradation process, liquid chromatography-mass spectrometry (LC-MS) detected the metabolites 2-aminobenzimidazole and 2-hydroxybenzimidazole. A putative carbendazim-hydrolyzing esterase gene was cloned from chromosomal DNA of djl-11 and showed 99% sequence homology to the mheI carbendazim-hydrolyzing esterase gene from Nocardioides sp. SG-4G

Phylogenetic tree based on the 16S rDNA sequence of strain djl-11 and related species.

<p>Strain djl-11 is marked with “▴”. The percentages of replicate trees in which the associated species clustered together in the bootstrap test (1000 replicates) are shown next to the branches. Genbank accession numbers are shown.</p

Effects of omitting and substituting NH₄NO₃ with organic substrates (N and C sources) on MBC biodegradation.

<p>The means of three independent experiments were plotted with error bars indicating standard deviations. Different letters above each column indicate significant differences among treatments (P<0.05).</p

Effects of metal ions on MBC biodegradation.

<p>The means of three independent experiments were plotted with error bars indicating standard deviations. Different letters above each column indicate significant differences among treatments (P<0.05).</p

Chemical kinetics of MBC, 2-AB and 2-HB in liquid culture of strain djl-11.

<p>◊, MBC; ○, 2-AB; △, 2-HB. Values are the means of three replicates with standard deviation.</p