Factors Affecting Growth and Interaction of Rough and Smooth Variants of Bacillus stearothermophilus. 1. Oxygen Tension and Temperature

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Abstract
SUMMARY— The influence of oxygen tension and temperature upon the growth and interaction of rough and smooth variants of Bacillus stearothermophilus NCA 1518 in pure and mixed populations was determined. The exclusion of oxygen did not prevent the growth of this organism but did influence the generation time of the two variants. At 55°C the pure rough population had a lower generation time when grown under anaerobic conditions while the generation time of the smooth variant was increased by low oxygen tension. Oxygen tension also affected the amounts of acid produced by the variants.The smooth variant produced more acid than the rough variant but the amount of acid was independent of oxygen availability. The rough variant, however, showed more acid accumulation as the oxygen tension was lowered. Temperature also affected differently the generation time of the variants. The smooth variant was more sensitive to a low temperature (45°C) and its generation time in pure population decreased more than three‐fold when the temperature was raised to 55°C. A further temperature increase to 65°C resulted in less than a two‐fold decrease in the generation time of the smooth variant. The rough variant showed approximately a two‐fold decrease in generation time for each increase of 10°C. The mixed populations became predominately smooth within 6‐8 hr of incubation.