INVOLVEMENT OF THE OMPA PROTEIN IN L-LEUCINE-INDUCED ACID SENSITIVITY

Escherichia coli grown in low-salt broth (LSB) showed rapid induction of acid sensitivity when L-leucine was added. Induction was strongly i nhibited by nalidixic acid and by tetracycline but only slightly by ch loramphenicol and rifampicin. Regulation of the effect appeared to inv olve H-NS, CysB, the ferric uptake regulator (Fur) and (p)ppGpp; ompA mutants were also unable to mount the response. Acid sensitization was greatly reduced by glucose, ferric chloride and ferrous sulphate but was not affected appreciably by phosphate or amiloride. Lesions abolis hing synthesis of integration host factor, the PhoE porin and NhaA ant iporter, did not prevent sensitization by L-leucine and lrp lesions on ly slightly affected the response. Organisms exposed to L-leucine were less susceptible to phage K3. Acid sensitivity depends on appearance of a new outer membrane (OM) pathway for protons and L-leucine-induced organisms may use a new pore formed from a modified OmpA protein.