The cold-shock stress response in Mycobacterium smegmatis induces the expression of a histone-like protein

The response of Mycobacterium smegmatis to a cold shock was investigated by monitoring changes in both growth and cellular protein composition of the organism. The nature of the cellular response was influenced by the magnitu de of the temperature reduction, with the shock from 37 degreesC to 10 degr eesC having the most widespread effect on growth, metabolism and protein co mposition. This 27 degreesC temperature reduction was associated with a lag period of 21-24 h before increases were seen in all the measured cellular activities. The response to cold shock was adaptive, with growth resuming a fter this period, albeit at a 50-fold slower rate. The synthesis of at leas t 15 proteins was induced during the lag period. Two distinct patterns of c old-induced synthesis were apparent, namely transient and continuous, indic ating the production of both cold-induced and cold-acclimation proteins. On e of these cold-shock proteins, CipMa, was identified as the histone-like p rotein, Hlp, of M. smegmatis, which is also induced during anaerobic-induce d dormancy. The corresponding gene demonstrated transient, cold-inducible e xpression with a five- to sevenfold increase in mRNA occurring 9-12 h after temperature shift. Although bacterial survival was unaffected, CipMa/Hlp k nockout mutants were unable to adapt metabolically to the cold shock and re sume growth, thus indicating a key role for CipMa in the cold-shock respons e.