Factors influencing the ability of Pseudomonas putida epI to degrade ethoprophos in soil

An ethoprophos-degrading Pseudomonas putida strain (epI) was used in laboratory-based experiments to inoculate soils containing residues of the nematicide. Inoculum densities as low as 104 cells g−1 were sufficient to degrade a fresh addition of ethoprophos within 16 days. P. putida epI was able to rapidly degrade aged as well as freshly applied ethoprophos residues. However, slower degradation of aged residues was observed in the later stages of incubation suggesting that a fraction of the pesticide residues had become inaccessible to the introduced bacteria. The effects of environmental and soil factors on the ability of P. putida epI to degrade ethoprophos were also studied. The bacterium was able to rapidly degrade ethoprophos at 20 and 35°C and at soil water potentials of −33 and −10 kPa. However, its degrading ability was significantly reduced but not completely inhibited at 5°C or at a soil water potential of −1500 kPa. The P. putida strain was active in soils with pH 6.8 and 8.3, but there was a complete loss of degrading ability in a soil with pH 5.4. Efficient degradation of ethoprophos by P. putida epI was observed in soils with organic matter contents varying from 0.3 to 8.5%. However, degradation was somewhat slower in the soil with the higher organic matter content, presumably due to increased pesticide adsorption and decreased bioavailability. The results indicate that the ethoprophos-degrading P. putida epI was efficient as a bioremediation agent in a range of environmental and soil conditions.