Inhibitory Effects of Two Common Agricultural Pesticides (Benomyl and Diazinon) on Growth of Pseudomonas putida Population

Pseudomonas putida is one of the most well-known bacteria and many strains of this bacterium have been reported from all over the world. Some strains are considered as the most important phosphate solubilizing agents in the soil, maximizing plant access to this element and as a result improve the plants growth. Several factors influence the natural growth of the bacteria in soil of which, the most important factors are pesticides. In the present study, effects of two widely used agricultural pesticides, Diazinon and Benomyl in different doses (250, 500, 1000, 2500 and 5000 mg/L) and at different temperatures (25, 30, 35, 40 and 450C) were studied on a selected isolate of P. putida. The results showed that both pesticides even at the lowest dose (250 mg/L) significantly reduced bacterial growth but not completely. The bacterial population growth was very slow in the range of recommended dose (1000 mg/L) for both pesticides. Benomyl did not stop bacterial growth completely at any of the selected doses, whereas Diazinon at concentrations of 2500 and 5000 mg/L became lethal for bacterial cells. At temperatures above 300C a significant decrease was observed in normal bacterial growth which was higher in the presence of both pesticides.