The presence of the dnaK heat shock gene could be demonstrated for B. longum NCC481, B. longum NCC490, B. longum NCC585, B. adolescentis NCC251, and B. breve NCC298. Induction of dnaK on the transcriptional level was shown for NCC251 and NCC481 by increasing temperatures. NCC251 showed an additional chaperone-induction after salt or bile-salt treatment. In both strains preconditioning with bile-salts protected against otherwise lethal concentrations thereof. NCC251 when subjected to a heat stress was able to survive an otherwise lethal temperature (55 degrees C). Cross-protection was demonstrated for NCC251 since salt pretreatment resulted in increased tolerance after freeze-thawing cycles or lethal heat stress.