Starvation-induced stress resistance development in a genetically modified Pseudomonas fluorescens strain

The response of a genetically modified Pseudomonas fluorescens to nutrient starvation and starvation-induced stress cross-protection were investigated. Strain BR12 was starved for carbon, nitrogen, phosphorus and sulphur individually and for all nutrients in defined mineral media and exposed for 6 h to chemical (ethanol 20%), oxidative (H2O2 20 mu M), osmotic (NaCl 3M), cold shock (0 degrees C) and heat shock (47 degrees C) stresses at different incubation times. Response to starvation and stress cross-protection development were evaluated by viable bacteria counts. There was a significant increase in resistance of late log phase cultures grown in rich medium to stress, except for ethanol, in all starvation situations. Multiple nutrient starved cultures were more resistant to stress than individual nutrient starved ones. This strain inoculated in oligotrophic stream water microcosms also showed the starvation-induced stress protection mechanism but it presented a higher resistance to ethanol than cultures starved in mineral media. The acquisition of nonspecific resistance to stress can favour the persistance of Genetically Modified Microorganisms (GMMos) in apparently unfavourable conditions.