SUMMARY: “Substrate-accelerated death” (Postgate & Hunter, 1963; 1964) occurred when a nitrogen-limited variant of NCTC 418 (Postgate & Hunter, 1962) was starved at growth temperature (37° or 40°) in aerated saline buffers containing ammonium ion; it was not observed when the parent strain of (MRE 162) was grown and starved under similar conditions. Sulphate ion increased the lethal effect of ammonium ion on the variant and magnesium did not abolish either the effect of ammonium or ammonium + sulphate ions. The variant differed from the parent strain in morphology, colonial appearance on nutrient agar, biochemical and immunological reactions and ability to synthesize polysaccharide. In ammonium-limited medium at 37° or 40° at a dilution rate near 0·25 hr the variant contained 3-5% and the parent strain 12-16% of dry weight as polysacharide; in spent medium or phosphate buffer at 37° with added glycerol the rate of polysaccharide synthesis by the variant was about 25% that of the parent strain. When grown in nitrogen-deficient medium with excess glycerol in batch culture, populations of the variant containing 25% polysaccharide were obtained; the survival of the polysaccharide-rich variant was not affected by ammonium ion.


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