Abstract

Salmonella encounters variables pH fluctuation during its life cycle and has been developed adaptative systems such as acid tolerance response (ATR) to survive at severe acidic environment. As part of on going investigation of stationary-phase specific acid resistance, we have searched for acid sensitive mutations in virulent Salmonella typhimurim UK-1 usin the MudJ fusion technique and two lethal selection procedures including DNP(dinitrophenol) selection media and microtiterplate selection method. Two acid sensitive mutations have been identified and designated, spatrK2, spatrK5. These mutations removed both stationary-phase acid tolerant effect and stationary-phase specific acid resistance. Non-specific histone like protein, H-NS and stationary-phase specific sigma factor, RpoS made little contribution to that system at respective single mutation(5-10 fold decrease). But, when both mutations were combined together, no acid resistance was achieved while acid tolerance response was still effective. Two dimensional SDS polyacrylamide gel electrophoresis showed new stationary-phase specific acid shock proteins as well as proteins already known. Not expectedly, the gels from acid adapted samples of both rpoS and hns mutation showed that double mutation of those regulators does not make change of the standard acid shock proteins. Only four acid shock proteins were regulated by these regulators, while fifteen proteins were newly identified as the members of acid shock response system by these regulators. These results implicate that stationary-phase acid resistance of that organism has RpoS/H-NS soubly dependent acid protective system and independent acid tolerance response system.

• Keywords: Salmonella; acid tolerance response; stationary-phase acid resistance; spatrK2; spatrK5; RpoS; H-NS