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 modifie d derivatives of the soil isolate Pseudomonas fluorescens R2f were sta rved in pure cultures for periods of up to 70 d. Cells were starved af ter harvesting at a point early in the stationary phase of the growth curve and all five strains demonstrated the ability to survive nutrien t deprivation and resuscitate rapidly when growth nutrients became ava ilable. No difference in total counts and metabolic activity was detec ted 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, Dur ing the starvation period there was a significant decrease in cell len gths of all five strains, however, there was no significant difference between the strains. The shape of the starved cells varied with the g rowth phase at which they had been harvested, Cells taken from early s tationary phase and starved produced predominantly rod-shaped cells wh ereas those taken from early log phase and starved produced small roun d cells, In experiments when the rifampicin-resistant mutant and the g enetically modified strain Art-3 were starved at early log phase the c ells were significantly smaller than respective cultures not exposed t o the nutrient limiting conditions, and there was no significant diffe rence in the response of the two strains, None of the cultures produce d ultramicrobacteria, and none of the cultures entered a non-culturabl e state, Starvation at different cell densities did not affect the rec overability of the cells. The results of this study demonstrate that r esponses to starvation conditions by the genetically modified and pare ntal strains are similar.