Degradation pathways of chlorsulfuron and metsulfuron-methyl by a Pseudomonas fluorescens strain

Sulfonylureas are a relatively new class of herbicides characterised by several aspects that make them particularly interesting in comparison with other products. Two microbial consortia able to grow on two sulfonylureas, chlorsulfuron and metsulfuronmethyl, were selected in laboratory conditions using as inocula soil samples previously treated with sulfonylurea herbicides and from a laboratory enrichment culture obtained with chlorsulfuron. From these mixed cultures, a Pseudomonas fluorescens strain called B2, was able to degrade in co-metabolic conditions with a rich medium in two weeks about 21% of metsulfuron-methyl and 32% of chlorsulfuron. For both herbicides, three microbial metabolites were detected and characterized, suggesting two different degradation pathways in which the cleavage of sulfonylurea bridge takes place. Chemical hydrolysis, performed in acidic condition, in order to determine the chemical degradation pathways and to obtain pure standard for HPLC analyses, allowed to identify different compounds from those obtained with biodegradation; in fact the cleavage of triazinic ring happened. These results suggest that microbiological and chemical degradation can follow different pathways.