Enhanced Degradation Of Diuron By Two Bacillus Species Isolated From Diuron Contaminated Sugarcane And Pineapple-Cultivated Soils In Kenya

It has been shown from diverse geographical locations that soils with repeated applications of pesticides display enhanced degradation of the pesticides which usually remain recalcitrant for a long time. In Kenya, agricultural activities have been using many different persistent pesticides for pest control. A study was undertaken to determine if the soils with repeated application history could show enhanced degradation of diuron. Laboratory degradation studies using non sterile sugarcane and pineapple-cultivated soils with over 5 years' application history showed enhanced degradation amounting to 80.2% and 86.2% of 5 mg/g initially applied diuron while sugarcane and pineapple-cultivated soils without application history degraded 34.4% and 48.4% of initially applied diuron after 146 days of incubation, respectively. Through liquid culture experiments with sugarcane and pineapple-cultivated soils and diuron as the carbon source, two bacterial strains capable of degrading diuron were isolated. By use of 16S rRNA comparative gene sequence technique, the strains were shown to be closely related to Bacillus muralis/Bacillus simplex and Bacillus pseudomycoides, respectively. These pure isolates were able to degrade diuron up to 51.0% and 54% of 50 mg/L after 46 days of incubation, respectively. The metabolites N-(3,4-dichlorophenyl)-N-methylurea and 3,4-dichloroaniline were reported as major by-products of diuron degradation in the two study sites with adapted microbes. The biodegradation capability of the strains isolated in this study indicates their microbial bioremediation potential for diuron mineralization in the contaminated soils.