The effect of growth temperature on Crl-dependent regulation of ^S activity in Salmonella enterica serovar Typhimurium

Unité de Génétique moléculaire and CNRS URA2172, Institut Pasteur, Paris, France

^* To whom correspondence should be addressed. Email: francoise.norel{at}pasteur.fr.

	Abstract

The small regulatory protein Crl favors association of the stationary phase sigma factor ^S (RpoS) with the core enzyme polymerase, and thereby increases ^S activity. Crl has a major physiological impact at low levels of ^S. Here, we report that Crl effects on ^S-dependent gene expression, the H₂O₂ resistance of Salmonella enterica serovar Typhimurium and its resistance to acidic pH, are larger at 28°C than at 37°C. Immunoblot experiments revealed a negative correlation between ^S and Crl levels: production of Crl was slightly higher at 28°C than at 37°C whereas ^S levels were about 2-fold lower at 28°C than at 37°C. At both temperatures, Crl was present in excess of ^S, and increasing Crl levels further did not increase the H₂O₂ resistance level of Salmonella and the expression of the ^S -dependent gene katE encoding the stationary phase catalase. In contrast, increasing ^S level rendered Salmonella more resistant to H₂O₂ at 28°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 Crl-dependent regulation of the katE gene and the H₂O₂ resistance are mediated mainly via an effect on ^S levels. In addition, our results revealed that ^S exerts a negative effect in the production of Crl in stationary phase when the cells contain high levels of ^S.