Levels of H+ and other monovalent cations in dormant and germinating spores of Bacillus megaterium

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Abstract
Previous investigators using the extent of uptake of the weak base methylamine to measure internal pH showed that the pH in the core region of dormant spores of B. megaterium is 6.3-6.5. Elevation of the internal pH of spores by 1.6 U had no significant effect on their degree of dormancy of their heat or UV light resistance. Surprisingly, the rate of methylamine uptake into dormant spores was slow (time for half-maximal uptake, 2.5 h at 24.degree. C). Most of the methylamine taken up by dormant spores was rapidly (time for half-maximal uptake, < 3 min) released during spore germination as the internal pH of spores rose to .apprx. 7.5. This rise in internal spore pH took place before dipicolinic acid release, was not abolished by inhibition of energy metabolism, and during germination at pH 8.0 was accompanied by a decrease in the pH of the germination medium. Also accompanying the rise in internal spore pH during germination was the release of > 80% of the spore K+ and Na+. The K+ was subsequently reabsorbed in an energy-dependent process. Between pH 6.2 and 7.8 internal spore pH has little effect on dormant spore properties. There is a strong permeability barrier in dormant spores to movement of charged molecules and small uncharged molecules. Extremely early in spore germination this permeability barrier is breached, allowing rapid release of internal monovalent cations (H+, Na+ and K+).

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