Pseudomonas aeruginosa UV-A-induced lethal effect: influence of salts, nutritional stress and pyocyanine.
The presence of NaCl in plating media shows an important protection against the Pseudomonas aeruginosa UV-A-induced lethal effect, contrasting with the known sensitizing action of salts on UV-A-irradiated Escherichia coli cells. MgSO4 exhibits a similar protection, but lower concentrations than for NaCl are needed to achieve the same effect. NaCl protection from lethal effects involves an osmotic mechanism, while MgSO4 could act by a different process. On the other hand, when cells grown in a complete medium are then incubated for 20 min in a synthetic medium and irradiated with UV-A, a very marked protection is obtained. This protection is dependent on protein synthesis, since treatment with tetracycline, during the nutritional stress, blocks its induction. These results offer a new example of cross-protection among different stressing agents. In our experimental conditions, natural phenazines of P. aeruginosa are not present in the cells, ruling out the possibility that these pigments act as photosensitizers. Conversely, pyocyanine (the major phenazine produced by this microorganism) prevents the UV-A killing effect in a concentration-dependent way when present in the irradiation media. Finally, UV-A irradiation induces, as in E. coli, the accumulation of guanosine tetraphosphate and guanosine pentaphosphate, although the physiological meaning of this finding has yet to be determined.
Fernández
R O
RO
Departamento de Radiobiología, Comisión Nacional de Energía Atómica, Buenos Aires, Argentina. rufernan@cnea.gov.ar
Pizarro
R A
RA
D003470:Culture Media; D008278:Magnesium Sulfate / Q000494:pharmacology; D010619:Phenazines / Q000494:pharmacology; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000254:growth & development / Q000528:radiation effects*; D011710:Pyocyanine; D012965:Sodium Chloride / Q000494:pharmacology; D014466:Ultraviolet Rays
D003470:Culture Media; D010619:Phenazines; D012965:Sodium Chloride; D008278:Magnesium Sulfate; D011710:Pyocyanine