Temperature-Sensitive Mutants of Streptococcus pneumoniae. I. Preparation and Characterization in Vitro of TemperatureSensitive Mutants of Type I S. pneumoniae

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Abstract
After exposure of type I Streptococcus pneumoniae to nitrosoguanidine, 13 temperature- sensitive (ts) mutants were selected that were restricted in capacity to form colonies on blood agar at 38 C. Whereas colony formation by the type I parent (ts+) was unaffected by a temperature of as high as 39 C, the ts mutants exhibited a spectrum of temperature sensitivity in which colony formation was inhibited significantly at 36 C, 37 C, 38 C, or 39 C. Growth of ts mutants at 38 C in broth was reduced or delayed relative to that of ts+ organisms under identical conditions. In general, there was a direct correlation between degree of temperature sensitivity and genetic stability. Mutants grown at a permissive temperature resembled the ts: type I parent in colonial morphology and properties of a-hemolysis, bile solubility, optochin sensitivity, and antibiotic sensitivity. Moreover, in vitro studies indicated that the mutants retained capsules of immunochemically reactive type I capsular polysaccharide.

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