SUMMARY: The growth rate of cells in a chemically defined medium was inversely proportional to the concentration of Mn between 15 and 300 mu;. In the presence of > 100 mu;-Mn, cells grew with doubling times of >60 min. Cessation of exponential growth due to a high concentration of Mn was most pronounced in cultures low in sulphur or carbon. This was due to the toxic effect of high Mn concentrations since dilution of cultures to a final Mn concentration of 15 mu; or less restored the growth rate to maximum. Sporulation depended upon the nature of the growth-limiting nutrient. The manganese effect on sporulation of sulphur-limited cells depended upon the concentration of glucose and the aeration rate in a qualitatively similar manner. The highest spore yield at optimal aeration rates was obtained when the initial Mn concentration in the medium was 10–30 mu;. Although the growth rate of bacteria in low-sulphate media was determined by the manganese concentration, its effect on sporulation frequency was independent of the growth rate.


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