HEAT AND COLD SHOCK RESPONSES IN DIFFERENT STRAINS OF THIOBACILLUS-FERROOXIDANS

Different strains of Thiobacillus ferrooxidans were examined for their ability to produce a heat shock and a cold shock response. Strain A1, heat shocked from 20 degrees to 35 degrees C, acquired thermotoleranc e, as it showed a 1000-fold reduction in cell mortality when exposed t o the supermaximum temperature of 42 degrees C, as compared to a non-h eat-shocked control. A heat shock from 25 degrees to 35 degrees C yiel ded similar results, although a higher degree of thermotolerance was a chieved for the shorter exposure times. Cultures heat shocked for 5 h showed a five-log reduction in viable counts after 41 h at 42 degrees C, whereas non-heat-shocked cultures showed a similar reduction in via bility in 28 h. Conferred thermotolerance was immediate and sustained for the duration of the exposure to 42 degrees C. Heat-shocked culture s were not significantly protected against loss of viability due to fr eezing (-15 degrees C for 24 h). Strain S2, cold shocked from 25 degre es to 10 degrees C, and strain D6, cold shocked from 25 degrees to 5 d egrees C, were not protected against freezing at -15 degrees C. An ana lysis of proteins extracted from heat-shocked cells of strain A1 showe d the presence of at least one newly induced protein and eight hyper-i nduced proteins. The molecular weights of the heat shock proteins were in the range of 15-80.3 kDa.