Toxic waste disposal in Escherichia coli

About 10% of the nalidixic acid-resistant (Nal(r)) mutants in a transposition-induced library exhibited a growth factor requirement as the result of cysH, icdA, metE, or purB mutation. Resistance in all of these mutants required a functional AcrAB-ToIC efflux pump, but the EmrAB-ToIC pump played no obvious role. Transcription of acrAB was increased in each type of Nal(r) mutant. In the icdA and purB mutants, each or the known signaling pathways appeared to be used in activating the AcrAB-ToIC pump. The metabolites that accumulate upstream of the blocks caused by the mutations are hypothesized to increase the levels of the AcrAB-ToIC pump, thereby removing nalidixic acid from the organism.