Activity, biomass and composition of microbial communities and their degradation pathways in exposed propazine soil.

Propazine is a s-triazine herbicide widely used for controlling weeds for crop production. Its persistence and contamination in environment nagatively affect crop growth and food safety. Elimination of propazine residues in the environment is critical for safe crop production. This study identified a microbial community able to degrade propazine in a farmland soil. About 94% of the applied propazine was degraded within 11 days of incubation when soil was treated with 10mgkg-1 propazine as the initial concentration. The process was accompanied by increased microbial biomass and activities of soil enzymes. Denaturing gradient gel electrophoresis (DGGE) revealed multiple bacterial strains in the community as well as dynamic change of the composition of microbial community with a reduced microbial diversity (H' from 3.325 to 2.78). Tracking the transcript level of degradative genes AtzB, AtzC and TrzN showed that these genes were induced by propazine and played important roles in the degradation process. The activities of catalase, dehydrogenase and phenol oxidase were stimulated by propazine exposure. Five degradation products (hydroxyl-, methylated-, dimeric-propazine, ammeline and ammelide) were characterized by UPLC-MS2 , revealing a biodegradation of propazine in soil. Several novel methylated and dimeric products of propazine were characterized in thepropazine-exposed soil. These data help understand the pathway, detailed mechanism and efficiency of propazine biodegradation in soil under realistic field condition.