The relative expression of the heat shock protein hsp18.55 gene was monitored in Lactobacillus plantarum ΔctsR and ΔftsH mutant strains. Transcription of the hsp18.55 gene was drastically repressed in the ΔctsR mutant of L. plantarum; conversely, significant transcriptional induction of the hsp18.55 gene was noted in the L. plantarum ΔftsH strain. Overall, these results suggest a possible regulation of the hsp18.55 gene by the alternative sigma H factor in L. plantarum. We also noted a similarity with the small heat shock gene (shs) locus of Lactobacillus brevis, which might indicate a possible evolutionary relationship
