Regulation and Self-Inhibition ofMicrosporum gypseumMacroconidia Germination

Abstract

Germination of Microsporum gypseum macroconidia was accompanied by the release of alkaline protease, calcium ions, and inorganic phosphate into the germination fluid. The rate of germination was greatest during the first 2 hr, decreasing thereafter. This decrease in rate was accompanied by a decrease in protease activity, which was caused by an interaction of the enzyme with the inorganic phosphate released from the spores and accumulated in the germination medium after 2 hr. Germination of high spore densities was regulated by the ratio of released phosphate to protease protein, resulting in a constant percentage of germination at both high and low spore densities. A germination-defective mutant strain failed to germinate normally and released excessively high concentrations of phosphate into the germination medium during the initial 2 hr of incubation. Addition of calcium ions to germination mutant macroconidia stabilized spore morphology, prevented protease inactivation, and allowed normal germ-tube outgrowth. The germination of macroconidia appears to be regulated by the release of phosphate ions, which then inhibit the alkaline protease.

Phosphate-Mediated Alteration of theMicrosporum gypseumGermination Protease Specificity for Substrate: Enhanced Keratinase Activity

“…Spore harvesting and germination procedures have been described previously (21,23). The alkaline germination protease was collected and partially purified by the method of Leighton and Stock (14).…”

“…The alkaline germination protease was collected and partially purified by the method of Leighton and Stock (14). Cell-free extract preparation also has been described (21,23).…”

“…Germination of these spores is accompanied by the release of a single alkaline protease into the germination medium (14). After germination initiation, the hydrolytic activity of the germination protease toward spore coat substrates is inhibited by inorganic phosphate (21,23).…”

Changes inMicrosporum gypseumMycelial Wall and Spore Coat Glycoproteins During Sporulation and Spore Germination

“…As previously shown, sporulation in M. gypseum appeared to result from cessation of aerial apical tip elongation with briefly continued cell expansion and septation (19). M. gypseum macroconidial germination is initiated by an alkaline protease (11,17) that is initially present in the mature spore coat and possibly released via lysosomal vesicles upon spore hydration (18).…”

“…Culture growth and harvesting. Growth in liquid cultures has been described previously (17,18). Sporulating cultures were grown in Roux flasks on an agar medium composed of: glucose, 1% (wt/vol); neopeptone (Difco), 1% (wt/vol); and agar, 2% (wt/vol).…”