The Responses of Soil Microbial Community to Glyphosate Stress Studied at Biochemical, Catabolic, and Genetic Levels.

Glyphosate, a broad-spectrum, non-selective and post-emergence organophosphate herbicide, is widely used in agriculture. We report here the in situ and ex situ effects of glyphosate on soil microbial community using culture-independent patterns of microbial biomass, phospholipid fatty acids (PLFAs), 16S rDNA-denaturing gradient gel electrophoresis (DGGE) and real-time quantitative PCR, as well as culture-dependent methods of plate enumeration and community level catabolic profiles (CLCPs). The results showed that microbial biomass reduced by 45%, and the numbers of cultivable bacteria and fungi decreased by 84% and 63%, respectively, whereas phosphobacteria were significantly enriched. PLFAs analysis showed that fungal and part of Gram-positive (G+) bacterial biomass were restrained remarkably by 29% and 21%, respectively, and followed by significant increase (38%) in the ratio of bacterial to fungal PLFAs in glyphosate input soils. On the other hand, the CLCPs showed that high dosage input of glyphosate had a significant boost on the catabolic activity of Gram-negative (G-) bacterial community. Furthermore, DGGE analysis indicated that the genetic diversity of bacterial community decreased in the soil contaminated by high dosage of glyphosate. Among 18 sequenced DGGE bands, 72% of which were related to G- bacteria. Real-time PCR result indicated that the copies of the glyphosate tolerance gene, 5-enolpyruvylshikimate-3-phosphate synthase gene (EPSPS), increased significantly in high glyphosate input soils. Our work demonstrated comprehensively that fungi and G+ bacteria were inhibited while G- bacteria played an important role in degrading glyphosate under the stress of high dosage of glyphosate. Soil fungi have been harmed even in the recommended concentration of glyphosate.