LAUSR

Abstract The aim of the current study was to evaluate the effects of four organophosphate pesticides on the siderophores producing soil microorganisms or plant growth promoting rhizobacteria (PGPR). Individual effects of acephate, glyphosate, monocrotophos and phorate as well as in combinations of two were tested against the five siderophore producing soils microorganisms viz, Pseudomonas fluorescens (NCIM-5096), Rhizobium leguminosarum (NCIM-2749), Bacillus brevis (NCIM-2532), Azotobacter vinelandii (NCIM-2821), and Salmonella typhimurium (NCIM-2501). The dose dependent effect was observed for the siderophore production assay. The effects of combinations were found to be more significant as compared to single pesticide(s). The overall sequence of adverse effect of the four pesticides on the siderophore production observed was: phorate > acephate > monocrotophos > glyphosate which was linear with the toxicity of pesticides. Further, it was noticed that PGPR strain Pseudomonas fluorescens (13–66%) was the least affected by the pesticides under study and Salmonella typhimurium (20–75%) was the most affected PGPR strain. The overall order of adverse effect of pesticides on the PGPR strains was as: Bacillus brevis (19–80%) > Salmonella typhimurium (20–75%) > Rhizobium leguminosarum (21–72%) > Azotobacter vinelandii (22–81%) > Pseudomonas fluorescens (13–66%). In combination, applications of Acpt + Phor have shown more adverse effects as compared to other combinations. Combination of Gly + Mono has no or least adverse effects on the PGPR strains. Present study may contribute to understand the role of siderophores and siderophores producing microorganisms in the metal ion uptake and risk associated with the applications of pesticides.