Effect of relA Activation on UV and Antibiotic Sensitivity

Abstract

The stringent response in starvation conditions is a well documented activation of the RelA protein, which synthesizes guanosine 3’, 5’ bisphosphate (ppGpp). Aside from inducing global changes in gene expression, increased cellular ppGpp levels have previously been + found to confer resistance to penicillin. We used Escherichia coli strains with relA + ts – ts (NF314As19); relA valS (NF536As19); and relA valS (NF537As19) geneotypes to determine if RelA activation conferred resistance to other antibiotics besides the Penicillins, as well as to ultraviolet radiation. It was experimentally found that partial activation of RelA + ts was achieved at 36 ° C in relA valS strains. While this strain was significantly more sensitive than the other two strains at 40 ° C to the five tested antibiotics (Ampicillin, – ts Chloramphenicol, Ciprofloxacin, Kanamycin and Vancomycin), the relA valS strain was + more sensitive than the relA strain at 40 ° C to three of the antibiotics (Ampicillin, + Chloramphenicol and Ciprofloxacin). relA bacteria were the least sensitive to UV radiation and both temperature sensitive strains were very strongly affected by UV radiation.