Blocking of protein synthesis pH 4.2 adaptation did not reduce the ATR attained by the cells, supporting the presence of a preshock inducible pH homeostasis system which does not require the synthesis of Att. In contrast to this, protein synthesis was obligately required during pH 5.0 adaptation for surviving L. acidophilus CRL 639 to challenge. In a similar way, protein synthesis has been reported necessary for a number of microorganisms, including Listeria monocytogenes(O' Driscol et al., 1996),