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Journal of Bacteriology, December 1998, p. 6148-6153, Vol. 180, No. 23
0021-9193/98/$00.00+0

Molecular Characterization of a Stress-Inducible Gene from Lactobacillus helveticus

Andrèas Smeds,1 Pekka Varmanen,2 and Airi Palva3,*

Agricultural Research Centre of Finland, Food Research Institute, Jokioinen 31600,1 and Faculty of Veterinary Medicine/Department of Basic Veterinary Sciences, 00014 University of Helsinki,3 Finland, and The Royal Veterinary and Agricultural University, Copenhagen, Denmark,2

Received 18 May 1998/Accepted 22 September 1998

A gene (htrA) coding for a stress-inducible HtrA-like protein from Lactobacillus helveticus CNRZ32 was cloned, sequenced, and characterized. The deduced amino acid sequence of the gene exhibited 30% identity with the HtrA protein from Escherichia coli; the putative catalytic triad and a PDZ domain that characterize the HtrA family of known bacterial serine proteases were also found in the sequence. Expression of the L. helveticus htrA gene in a variety of stress conditions was analyzed at the transcriptional level. The strongest induction, resulting in over an eightfold increase in the htrA transcription level, was found in growing CNRZ32 cells exposed to 4% (wt/vol) NaCl. Enhanced htrA mRNA expression was also seen in CNRZ32 cells after exposure to puromycin, ethanol, or heat. The reporter gene gusA was integrated in the Lactobacillus chromosome downstream of the htrA promoter by a double-crossover event which also interrupted the wild-type gene. The expression of gusA in the stress conditions tested was similar to that of htrA itself. In addition, the presence of an intact htrA gene facilitated growth under heat stress but not under salt stress.

* Corresponding author. Mailing address: Faculty of Veterinary Medicine/Department of Basic Veterinary Sciences, P.O. 57, 00014 University of Helsinki, Finland. Phone: 358-9-70849531. Fax: 358-9-70849799. E-mail: airi.palva{at}helsinki.fi.

Journal of Bacteriology, December 1998, p. 6148-6153, Vol. 180, No. 23
0021-9193/98/$00.00+0


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