Survival of parental and genetically modified derivatives of a soil isolated Pseudomonas fluorescens under nutrient-limiting conditions

Wild type, a rifampicin-resistant mutant and three genetically modified derivatives of the soil isolate Pseudomonas fluorescens R2f were starved in pure cultures for periods of up to 70 d. Cells were starved after harvesting at a point early in the stationary phase of the growth curve and all five strains demonstrated the ability to survive nutrient deprivation and resuscitate rapidly when growth nutrients became available. No difference in total counts and metabolic activity was detected between the strains. Plate counts were similar for all strains up to day 35. Wild type and the rifampicin-resistant mutant strain showed greater recovery than the genetically modified strains on day 70. During the starvation period there was a significant decrease in cell lengths of all five strains, however, there was no significant difference between the strains. The shape of the starved cells varied with the growth phase at which they had been harvested. Cells taken from early stationary phase and starved produced predominantly rod-shaped cells whereas those taken from early log phase and starved produced small round cells. In experiments when the rifampicin-resistant mutant and the genetically modified strain Art-3 were starved at early log phase the cells were significantly smaller than respective cultures not exposed to the nutrient limiting conditions, and there was no significant difference in the response of the two strains. None of the cultures produced ultramicrobacteria, and none of the cultures entered a non-culturable state. Starvation at different cell densities did not affect the recoverability of the cells. The results of this study demonstrate that responses to starvation conditions by the genetically modified and parental strains are similar.