Influence of Temperature on the Growth of Psychrophilic Strains of Bacillus

Abstract

Specific growth rates, doubling times, and temperature characteristics were determined for 12 cultures of 9 species of Bacillus that had been isolated from milk and found able to grow at low temperatures. Cultures of Group A, psychrophilic strains of B. subtilis, B. circulans, and B. coagulans, grew at 0 ± 1 C and had growth characteristics similar to those reported for psychrophilic species of Pseudomonas. Eight cultures of Group B had minimal growth temperatures of 5 to 7 C and other growth characteristics between those reported for psychrophilic species Pseudomonas and those reported for mesophilic bacteria. Doubling times for B. circulans RH3, B. laterosporus, and B. coagulans F8 in milk at 7.2 C were 5, 5.5, and 7 hours. These three cultures produced fruity flavor in milk, followed by the production of rancidity by B. circulans RH3 and unclean flavor by the other two cultures. Plate counts at the time of detecting off-flavor were between 1.0 × 106 and 1.0 × 107 per milliliter for B. coagulans F8 and B. laterosporus and about 5.0 × 107 for B. circulans RH3. © 1971, American Dairy Science Association. All rights reserved.