ENVIRONMENTAL STRESSES ON SPORE POPULATIONS OF BACILLUS STEAROTHERMOPHILUS.

Heat-shocking spores at 110 C in 20% sucrose solutions decreased the percentage of the rough variant in a mixed population (rough and smooth variants) of strain M. Heat-shocking spores of the rough variant of strain NCA 1518 in 20% sucrose produced a decline in the number which germinated, whereas the smooth variant of strain NCA 1518 increased in the number which germinated. By the use of phase microscopy and plate counts, from the same incubated spore suspension in distilled water, heat-induced dormancy was demonstrated at 52 C. Dormancy also occurred in 20% sucrose solutions when held at room temperatures. Heat-shocking spores of strain M in 20% sucrose solutions and plating immediately after 24- and 48-hr holding periods at 25 C produced a decline in the total population with the percentage of rough variant increasing with time. A second heat shock produced only an increase in the rough variant.