Stress- and Growth Phase-Associated Proteins of Clostridium acetobutylicum
Applied and Environmental Microbiology
The response of Clostridium acetobutylicum ATCC 4259 to the stresses produced by a temperature upshift from 28°C to 45°C and by exposure of the organisms to 0.1 % n-butanol or to air was examined by analysis of pulse-labeled proteins. The stress response was the induction of the synthesis of a number of proteins, some of which were elicited by the three forms of stress. Eleven heat shock proteins were identified by two-dimensional electrophoresis, as were two proteins whose synthesis was heat
... nsitive. In the absence of applied stress, the synthesis of four proteins was found to be associated with the growth phase in batch culture; three of these proteins had a higher rate of de novo synthesis when the cells entered the solvent production phase. One of the stress-induced proteins, hsp74, was partially purified an found to be immunologically related to Escherichia coli heat shock protein DnaK. The similarities of the proteins induced at the onset of solventogenesis and by stress suggest a relationship between the two processes. Clostridiijumn acetohittvlicum cells growing in batch culture ferment sugars to butyric and acetic acids, which decrease the external pH to below 5 at the end of exponential phase (for reviews, see references 17 and 37). During stationary phase, the sugar and the preformed acids are converted to solvents (butanol, acetone, and ethanol) and traces of acetoin; H2 and CO, are also produced. The switch of catabolism to solventogenesis has the effect of raising the medium pH. As stationary phase progresses, the cells undergo a series of morphological and physiological changes in motility, shape, and granulose content, culminating in the formation of endospores (16). The ability to produce solvents is associated with an early step in sporulation (17, 37). The accumulation of solvents causes the cell membranes to become progressively more permeable to small molecules, as shown by decreased rates of glucose uptake and glycolysis, dissipation of the H+ gradient across the cell membrane (42), loss of internal glycolytic intermediates (15). and decrease in the viability of the vegetative cells (24). Thus, it is likely that solvents, endogenously produced membranechaotropic agents, are stressful to the cells.