No abstract

This work is a part of the PhD of the first author and was carried out in collaboration betweenall authors. Author BBM designed the study, authors BBM and IA performed the experiment and statistical analysis, wrote the protocol, and wrote the first draft of the manuscript. Authors JI and LN supervised the study and managed the literature searches, author EEF did the genotypic analysis. All authors read and approved the final manuscript.

Background: Soil microorganisms are exposed to herbicides after treatment, which leads to their interaction. The result of this interaction may be the degradation of the herbicides by the microorganisms and by the way, they use the degradation products as an energy source for their own physiological processes, or herbicides have a toxic effect on these microorganisms. Herbicide toxicity becomes severe instantly after application when its concentration in soil is the highest. Paraquat is one of the most widely used herbicides in agriculture; inappropriate use of this herbicide represents an immense pollution problem for soil, therefore on microorganisms. However, the knowledge about the effect of paraquat on soil microorganisms has been limited. Objectives: The purpose of the current study was to determine the effect of paraquat application on four nitrogen-fixing bacteria: Pantoea agglomerans, Rhizobium nepotum, Rhizobium tibeticum and Rhizobium radiobacter. Methods: Paraquat was applied as the sole source of carbon at a rate (0 g/L, 0.5 g/L, 1 g/L, 3 g/L, 6 g/L and 12 g/L). The effect of paraquat treatments was determined by agar diffusion method and the rate of the growth of bacterial colonies in each treatment. Results: In the agar diffusion method, the bacterial strains were inhibited by paraquat, in which the inhibition zone was wider with the increase of paraquat concentration; also, analysis of the Colony Forming Units (CFUs) mostly showed a declining in bacterial growth. In comparison with the control, the growth of the four strains was decreased by increasing the paraquat concentration. Comparing strains with each other, Pantoea agglomerans is the most resistant strain to paraquat. Conclusion: Our study has shown the impact of the irrational use of pesticide upon the beneficial bacteria in question. For that, the results of this research have a positive impact on the natural environment, which will have tangible social and economic impacts.

The presence of residual pesticides in the soil affect the microbial Communities, as well the continuous use of pesticides exacerbates this problem. Glyphosate is one of the most used herbicides in the world. Up to date several studies have evaluated the tolerance and resistance of bacteria to glyphosate. Nitrogen-fixing bacteria play an important role in soil fertility; thus, the alteration of these bacterial communities decrease soil fertility. The objective of this study was to evaluate the effect of glyphosate application on four bacterial strains Pantoea agglomerans, Rhizobium nepotum, Rhizobium radiobacter, and Rhizobium tibeticum. Glyphosate was applied as the sole source of carbon at the rate (0 g/l, 0.5 g/l, 1g/l, 3g/l, 6g/l and 12 g/l) with two methods. Microbial growth was measured by the Colony Forming Units (CFUs /ml) method. Comparing with the control, our results showed that the growth of the four strains decreased by increasing the concentration of glyphosate. The four strains have shown resistance to glyphosate in the direct enrichment compared to the continued enrichment method. Comparing strains with each other, Rhizobium radiobacter is the most resistant strain to glyphosate.

No abstract