REGULATORY COMPONENTS, INCLUDING INTEGRATION HOST FACTOR, CYSB AND H-NS, THAT INFLUENCE PH RESPONSES IN ESCHERICHIA-COLI

This review describes a range of pH responses. Some are only induced i f relevant DNA is brought to an appropriately supercoiled configuratio n by DNA gyrase and bent by the action of, for example, integration ho st factor (IHF). Bending may allow transcription by bringing activator s into juxtaposition with RNA polymerase, which is CysB-associated in several of the responses. Control of arginine decarboxylase (AdiA) syn thesis at acid pH is of the above type, with dependence on the presenc e of gyrase, H-NS, IHF and CysB; acid induction of LysU has similar re quirements but also needs Lrp; lysine decarboxylase (CadA) formation a t acid pH is controlled quite differently, needing the CadC activator and interaction of lysine/lysine permease; H-NS probably reverses indu ction by CadC. The Hyd components of formic hydrogenlyase are induced by acid under anaerobiosis; a transcriptional activator is involved an d Fur may also function in regulation. Acid tolerance induced at low p H in log-phase cells needs CysB and PhoE but not DNA gyrase; tolerance is reduced by NaCl but not affected by Fe3+, Fe2+, glucose/cAMP or by lrp, him, fur, hns or nhaA/B lesions. Alkali tolerance (habituation), induced at pH(0) 8.5-9.0, probably involves DNA supercoiling and bend ing; the induction process needs IHF, CysB, PhoE, NhaA, TonB and Fur a nd is glucose-repressed; tolerance may result from Na+ efflux catalyse d by the NhaA antiporter, which is induced at pH(0) 9.0. Alkali sensit ivity induced at pH(0) 5.5 also requires gyrase, IHF and CysB, but H-N S, Lrp, NhaA and OmpC are also needed and induction is abolished by Na Cl. Salt-induced acid sensitivity results from PhoE formation and is b locked by glucose (reversed by cAMP), FeCl3 and hns and relA lesions, the effect of relA being envZ-suppressed. Acid sensitivity induction ( ASI) at pH(0) 9.0 needs H-NS, is inhibited by FeCl3 and amiloride, and is associated with alkyl hydroperoxide reductase synthesis. Leucine-i nduced acid sensitivity needs gyrase, CysB, H-NS, Fur, OmpA and RelA, is inhibited by Fe3+, Fe2+, tetracycline, glucose and nalidixic acid, but not by chloramphenicol; increased outer membrane proton passage ma y result from OmpA modification.