Biodegradation of triazine herbicide metribuzin by the strain Bacillus sp. N1

By enrichment culturing of soil contaminated with metribuzin, a highly efficient metribuzin degrading bacterium, Bacillus sp. N1, was isolated. This strain grows using metribuzin at 5.0% (v/v) as the sole nitrogen source in a liquid medium. Optimal metribuzin degradation occurred at a temperature of 30ºC and at pH 7.0. With an initial concentration of 20 mg L(-1), the degradation rate was 73.5% in 120 h. If the initial concentrations were higher than 50 mg L(-1), the biodegradation rates decreased as the metribuzin concentrations increased. When the concentration was 100 mg L(-1), the degradation rate was only 45%. Degradation followed the pesticide degradation kinetic equation at initial concentrations between 5 mg L(-1) and 50 mg L(-1). When the metribuzin contaminated soil was mixed with strain N1 (with the concentration of metribuzin being 20 mg L(-1) and the inoculation rate of 10(11) g(-1) dry soil), the degradation rate of the metribuzin was 66.4% in 30 days, while the degradation rate of metribuzin was only 19.4% in the control soil without the strain N1. These results indicate that the strain N1 can significantly increase the degradation rate of metribuzin in contaminated soil.