Survival of a lacZY‐Containing Pseudomonas putida Strain under Stressful Abiotic Soil Conditions

Abstract

AbstractLittle is known about the effect of soil factors on genetically altered bacteria. We altered Pseudomonas putida PH6 to contain the Escherichia coli genes for lactose utilization (lacZY). Except for lactose utilization, the genetically altered mutant, P. putida PH6(L1019), and the wild type strain were indistinguishable in the tests we employed. Both strains were tested for survival in eight different soils, and in one soil at temperatures of 15, 25, 35, and 40°C and soil water pressures of −0.03, −0.07, and −1.5 MPa. Few differences in survival of the two strains were observed in seven of the eight soils, but in the most acid soil (pH 5.0), numbers of PH6 were at least 100‐fold higher 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 104 colony‐forming units (CFU) g−1 of soil. Neither PH6 nor PH6(L1019) survived at 40°C after 3 d, and few differences in survival were observed between the two strains at 15 and 25°C. At 35°C, PH6 declined from ≈108 to ≈103 CFU g−1 of soil after 35 d, whereas PH6(L1019) declined from ≈108 CFU g−1 of soil to below the limit of detection (<10 CFU g−1 of soil) after 14 d. Few differences in survival between PH6 and PH6(L1019) were observed at −0.03 and −0.07 MPa, but at −1.5 MPa, PH6 survival was greater than PH6(L1019) at all sampling times. These results are the first to suggest that a soil abiotic factor can exert differences in survival between a wild type and genetically altered bacterium.