EXPRESSION OF THE COLD-SHOCK GENE CSPB IN SALMONELLA-TYPHIMURIUM OCCURS BELOW A THRESHOLD TEMPERATURE

Previous studies have shown that several bacterial species exhibit a m ultigenic response following temperature downshift (cold shock). Evide nce for such a response in Salmonella typhimurium is reported, based o n the isolation of a range of low-induction-temperature gene fusions c ontaining Mudlux insertions. The fusions exhibited different levels of basal light at 30 degrees C, and were induced at different rates and to different degrees over several hours following a reduction in tempe rature to 10 degrees C. Of the Mudlux gene fusions isolated, one was f ound which produced essentially no light when grown at 30 degrees C bu t exhibited rapid and high-level induction when the temperature was re duced to 10 degrees C. The target of this gene fusion (which was named cspB) was shown to lie adjacent to the umuDC operon and to encode a h omologue of the major cold-shock protein of Escherichia coli, CspA. Lu minescence studies revealed that substantial light production occurred from the cspB::Mudlux fusion at or below 22 degrees C but not at high er temperatures, even following a temperature drop from 30 degrees C. Moreover, cspB mRNA levels were found to mimic this pattern of lumines cence, suggesting that cspB expression occurs below a defined temperat ure threshold. The cspB mRNA was also found to be very stable at 10 de grees C but to become highly unstable when the temperature was raised towards the threshold temperature, even in the presence of rifampicin. Existing cellular RNases therefore appear to mediate the decay of csp B mRNA at high temperatures, but are incapable of this at low temperat ures.