Growth phase-associated changes in protein expression in Mycobacterium smegmatis identify a new low molecular weight heat shock protein

De novo protein synthesis and the heat-shock response during different stag es of bacterial culture of Mycobacterium smegmatis LR222 were investigated. A discontinuance in the increase in number of colony forming units occurre d at mid-exponential phase of growth. This coincided with a plateau in the ATP content of the culture, a reduction in the synthesis of exponential pha se proteins (58, 30.5, and 20 kDa), a transitory synthesis of a 32 kDa prot ein and the induction of stationary-phase proteins (48, 46, 31, 25, and 20 kDa). The response to heat shock showed a growth-phase dependency, with the highest fold-induction of the 75 kDa (DnaK) protein occurring during the t ransitory cessation in the increase in CFU, while the greatest increase of the 95 kDa, 66 kDa (GroEL), and similar to 17 kDa (a doublet) proteins occu rred during stationary phase. The similar to 17 kDa doublet was resolved in to four polypeptides by two-dimensional electrophoresis. Mass spectrometric analysis of the sequence of one polypeptide (named Hsp17-2, 16.8 kDa) reve aled significant homology to a conserved, 16.2 kDa, hypothetical protein of unknown function in Mycobacterium tuberculosis H37Rv. The increased synthe sis of Hsp17-2 in response to heat shock suggests that it may represent a n ew low molecular weight heat shock protein. (C) 2001 Harcourt Publishers Lt d.