Metsulfuron Degrading Bacteria, Degradation Characteristics And Application Base

Metsulfuron-methyl belongs to the group of sulfonylurea herbicides characterized by low application rates and high herbicidal activity. It is widely used for weed control in cereals and other crops and is highly active against a wide range of broadleaf weeds. The residues of metsulfuron-methyl in soil have been reported to cause damage to ratation and substitution crops. There is a need to develop a method for the detoxification of metsulfuron-methyl residues in agricultural soil and elimination of its harmful effect on crops. In the present study, a strain MD of Curvularia sp. capable of degrading metsulfuron-methyl was isolated from soil. The kinetics of metsulfuron-methyl in soil and water degraded by the isolated strain Curvularia sp. MD and the biodegradation pathway was investigated. The possibility of using the isolated strain MD to detoxify metsulfuron-methyl residues in water and soil and to eliminate the harmful effect was also studied. The main results were summarized as follows:1. One fungal strain MD capable of utilizing metsulfuron-methyl as sole carbon source was isolated from soil. The strain is identified as Curvularia sp. according to its physiological and biochemical characteristics. In pure culture, optimal conditions for biodegradation is under 30 and pH7.0. The rate constants for degradation of metsulfuron-methyl at concentrations of 0.10,1.0 and 10.0mg/L by the isolated strain MD were measured to be 0.4259,0.3465 and 0.169, respectively. The differences among the degradation rates indicate that the concentration of metsulfuron-methyl affects degradation rate significantly. It could be concluded that the isolated strain MD is more suitable to degrade metsulfuron-methyl at low concentrations.2. Four possible compounds were determined as degradation products of metsulfuron-methly by the isolated strain MD with HPLC-MS. Based on the possible degradation products, Microbial degradation pathways of metsulfuron-methyl is concluded as follows: after the cleavage of the sulfonylurea bridge, 2-amino-4-methoxy-6-methyl-triazine is demethylated and the annularity reaction of sulphanilamide occurs. In that the strain MD can utilize metsulfuron-methyl as sole carbon source, the metabolites might ultimately mineralize into CO2.3. From the experiments of metsulfuron-methyl degradation in soils, rate constants for the degradation of metsulfuron-methyl in nonsterile soil, nosterile soil inoculated with MD, sterile soil and sterile soil inoculated with MD were determined to be 0.0079,0.0298,0.0029 and 0.0219 at l0.0mg/kg, 0.0372,0.1010,0.0180 and 0.0600 at l.0mg/kg, respectively. The degradation rate of metsulfuron-methyl at l.0mg/kg in soil is more rapid than at l0.0mg/kg. In water culture trials, crops grow well with the increase of inoculated time. Biomass of seedling planted 10 days after inoculation was similar to that of the control with percentages of 94.4%, 137.2% and 99.7% for cotton, bean and corn .respectively. For soil trials, similar results were obtained and biomass of cotton ,bean and corn, were 82.0%, 95.5% and 90.1% of the control, respectively.