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Abstract
Two genes, relA and spoT, are known to be responsible for the production of ppGpp when E. coli cells undergoing amino acid starvation initiate the stringent response. In this modified state, cells have been reported to up-regulate processes which confer resistance to antibiotics. However, the individual contribution of relA was not separated from potential effects of spoT. By using 3 strains of E. coli: B23 (wild-type), 58-161 ( spoT), and w1655 ( relA, spoT) grown in modified M9 media, we attempted to characterize the impact of ppGpp synthase (RelA) in the induction of a stringent response, and whether there was a variation in stringency generated by exposure to kanamycin or amino acid starvation. Our results showed both treatments to have similar effects across all three E. coli strains, with no significant differences attributed to the particular genotypes. Furthermore, neither treatment appeared to confer antibiotic cross-protection upon subsequent exposure to sublethal concentrations of ampicillin.