Influence of Osmotic Pressure upon Spore Germination

Abstract

Spores of Bacillus mycoides were grown on nutrient agar slants and freed from metabolic products by repeated washings and centrifugations. Nutrients used were plain infusion broth and peptone solutions, adjusted to pH 7. Osmotic pressure (O.P.) was varied by addition of sterile 10% NaCl. O.P. was determined by the freezing point method. The highest NaCl concentration used was only slightly greater than that in physiological saline. Rate of germination was determined by direct observation at short time-intervals in hanging drop preparations sealed in a moisture chamber. The % of germinating spores was determined by actual count of 100 spores. Germination was most rapid at lower O.P. There appears to be a definite limiting concentration of food supply (0.025% for peptone) below which no germination occurs, regardless of O.P. when minimal nutritional requirements are exceeded, the increased concentration of food may retard germination, because of unfavorable increase in O.P. In very dilute nutrient solutions, salts have an increased toxic effect. Optimum O.P. for vegetative growth is higher than that required for germination, and it varies with nature of nutrient medium. A rather definite limiting O.P. for germination exists at 36-40 atms., which appears to be independent of nature of nutrient. In some cases inhibition of germination is brought about by the chemical activity of the salt, bivalent salts being particularly effective.