Exposure effect of fungicide kasugamycin on bacterial community in natural river sediment.

The degradation of kasugamycin in water and the effects of kasugamycin on the bacterial communities in sediment and overlying water were analyzed over a 30-day period. Kasugamycin is generally regarded as nontoxic to microorganisms, but in this study we demonstrated that kasugamycin inhibited the growth of some aquatic bacteria but also stimulated the growth of other resistant bacteria. Microcosms were contaminated with kasugamycin at the 168.4 mg/L (700 times field application rate), and 1462.9 mg/L (6000 times field application rate). The percentages of kasugamycin degraded after 30 days of exposure were 34.1%, and 12.1% in the overlying water treated with 168.4 mg/L and 1462.9 mg/L, respectively. The degradation rates of kanamycin after 30 days of exposure were 1.92 mg/L/day for 164.8 mg/L treated water and 5.88 mg/L/day for 1462.9 mg/L treated water. Degradation rate of kasugamycin in overlying water was associated with an increase in the concentration of kasugamycin. Comparison of DGGE (denaturing gradient gel electrophoresis) profiles showed that the bacterial communities in treated microcosms were varied. Certain species were eliminated whereas some species were stimulated by the application of kasugamycin. The DGGE profiles and UPGMA (unweighted pair-group method using arithmetic averages) dendrograms revealed that the bacterial communities were more complex in treated sediment than in treated overlying water.