Effect of growth temperature on Crl-dependent regulation of us activity in Salmonella enterica serovar typhimurium

The small regulatory protein Crl favors association of the stationary-phase sigma factor sigma(s) (RpoS) with the core enzyme polymerase and thereby increases us activity. Crl has a major physiological impact at low levels of us. Here, we report that the Crl effects on us-dependent gene expression, the H2O, resistance of Salmonella enterica serovar Typhimurium, and the resistance of this organism to acidic pH are greater at 28 degrees C than at 37 degrees C. Immunoblot experiments revealed a negative correlation between us and Crl levels; the production of Cri was slightly greater at 28 degrees C than at 37 degrees C, whereas the us levels were about twofold lower at 28 degrees C than at 37 degrees C. At both temperatures, Crl was present in excess of us, and increasing the CA level further did not increase the H2O2 resistance level of Salmonella and the expression of the us-dependent gene katE encoding the stationary-phase catalase. In contrast, increasing the us level rendered Salmonella more resistant to H2O2 at 28 degrees C, increased the expression of katE, and reduced the magnitude of Crl activation. In addition, the effect of Crl on katE transcription in vitro was not dependent on temperature. These results suggest that the effect of temperature on Cri-dependent regulation of the katE gene and H2O2 resistance are mediated mainly via an effect on sigma(s) levels. In addition, our results revealed that us exerts a negative effect on the production of Crl in stationary phase when the cells contain high levels of sigma(s).