Abstract
The bacterial heat shock response is characterized by the elevated expression of a number of chaperone complexes and transcriptional regulators, including the DnaJ and the HrcA proteins. Genome analysis of Bifidobacterium breve UCC 2003 revealed a second copy of a dnaJ gene, named dnaJ2, which is flanked by the hrcA gene in a genetic constellation that appears to be unique to the actinobacteria. Phylogenetic analysis using 53 bacterial dnaJ sequences, including both dnaJ1 and dnaJ2 sequences, suggests that these genes have followed a different evolutionary development. Furthermore, the B. breve UCC 2003 dnaJ2 gene seems to be regulated in a manner that is different from that of the previously characterized dnaJ1 gene. The dnaJ2 gene, which was shown to be part of a 2.3-kb bicistronic operon with hrcA, was induced by osmotic shock but not significantly by heat stress. This induction pattern is unlike those of other characterized dnaJ genes and may be indicative of a unique stress adaptation strategy by this commensal microorganism.