SURVIVAL OF A LACZY-CONTAINING PSEUDOMONAS-PUTIDA STRAIN UNDER STRESSFUL ABIOTIC SOIL-CONDITIONS

Little is known about the effect of soil factors on genetically altere d bacteria. We altered Pseudomonas putida PH6 to contain the Escherich ia coli genes for lactose utilization (lacZY). Except for lactose util ization, the genetically altered mutant, P. putida PH6(L1019), and the wild type strain were indistinguishable in the tests we employed. Bot h strains were tested for survival in eight different soils, and in on e soil at temperatures of 15, 25, 35, and 40-degrees-C and soil water pressures of -0.03, -0.07, and -1.5 MPa. Few differences in survival o f the two strains were observed in seven of the eight soils, but in th e most acid soil (pH 5.0), numbers of PH6 were at least 100-fold highe r than PH6(L1019) after 28 d. The percentage of lactose-positive (lac) isolates averaged >95% in all eight soils unless PH6(L1019) numbers declined below 10(4) colony-forming units (CFU) g-1 of soil. Neither P H6 nor PH6(L1019) survived at 40-degrees-C after 3 d, and few differen ces in survival were observed between the two strains at 15 and 25-deg rees-C. At 35-degrees-C, PH6 declined from almost equal to 10(8) to al most-equal-to 10(3) CFU g-1 of soil after 35 d, whereas PH6(L1019) dec lined from almost-equal-to 10(8) CFU g-1 of soil to below the limit of detection (<10 CFU g-1 of soil) after 14 d. Few differences in surviv al between PH6 and PH6(L1019) were observed at -0.03 and -0.07 MPa, bu t at -1.5 MPa, PH6 survival was greater than PH6(L1019) at all samplin g times. These results are the first to suggest that a soil abiotic fa ctor can exert differences in survival between a wild type and genetic ally altered bacterium.