Activation and germination characteristics observed in endospores of thermophilic strains of Bacillus

Abstract

The properties of endospores of some thermophilic strains of Bacillus were examined. Included were strains isolated from thermal pools and springs in Yellowstone National Park, a strain of B. thermodenitrificans and two strains of B. stearothermophilus, ATCC 7953 (smooth) and T-10. The spores of thermophilic strains of Bacillus contained relatively high levels of dipicolinic acid ranging from 11-14.8% of the spore dry weight, while the calcium levels were similar to those observed in other bacterial endospores including mesophilic bacilli and thermophilic actinomycetes. Spore populations of thermophilic bacilli could not be effectively germinated in solutions of sodium phosphate alone but germinated well in solutions supplemented with one of a variety of organic compounds. Solutions containing L-valine or L-leucine were particularly effective. A wide range of pH permitted the germination of fractions of spore populations, however, optimum germination was observed only at pH values of 6.0 and above. A range in incubation temperatures of less than 25 degrees C permitted 50% or more of the spores of each of the organisms to germinate. Freshly prepared spore did not germinate, but these spores germinated rapidly and completely if they were heated for 30 min at 100 degrees C just prior to germination testing, i.e., the spores were heat activatable. However, spores of thermophilic bacilli could also be activated by shifting them to and holding them at temperatures below their optimum growth temperature of 65 degrees C. Of the ten temperatures tested, ranging from 4 degrees C through 50 degrees C, the optimum reduced temperature for spore activation was 30 degrees C.