Factors influencing the ability of Pseudomonas putida strains epI and II to degrade the organophosphate ethoprophos

TWO strains of Pseudomonas putida (epI and epII), isolated previously from ethoprophos-treated soil, were able to degrade ethoprophos (10 mg I-1) in a mineral salts medium plus nitrogen (MSMN) in less than 50 h with a concurr ent population growth. Addition of glucose or succinate to MSMN did not inf luence the degrading ability of Ps. putida epI, but increased the lag phase before rapid degradation commenced with Ps. putida epII. The degrading abi lity of the two isolates was lost when the pesticide provided the sole sour ce of phosphorus. Degradation of ethoprophos was most rapid when bacterial cultures were incubated at 25 and 37 degrees C. Pseudomonas putida epI was capable of completely degrading ethoprophos at a slow rate at 5 degrees C, compared with Ps. putida epII which could not completely degrade ethopropho s at the same time. Pseudomonas putida epI was capable of degrading ethopro phos when only 60 cells ml(-1) were used as initial inoculum. In contrast, Ps. putida epII was able to totally degrade ethoprophos when inoculum densi ties of 600 cells ml(-1) or higher were used. In general, longer lag phases accompanied the lower inoculum levels. Both isolates rapidly degraded etho prophos in MSMN at pHs ranging from 5.5 to 7.6, but not at pH 5 or below.