Proteolytic activity of different Candida strains

Methods: The Candida strains used were C. albicans, C. dubliniensis, C. guilliermondii, C. glabrata, C. krusei and C. tropicalis. The yeasts were grown in YPD-medium at 37ºC for 24 h. The cells were harvested by centrifugation and disrupted by sonication. The gelatinolytic activity of both cell-fractions and 10 times concentrated media fractions were tested with gelatin-zymography using two different buffers (pH 4.0 and 7.6).

Results: All the species except C. guilliermondii yielded multiple bands in gelatin-zymography. Both strains and fractions of C.albicans and C. dubliniensis yielded bands of 50 and 45 kDa respectively, only at pH 4.0. The media fractions of the strains of C. krusei and C. glabrata did not degrade gelatin but the cell fractions at both pHs yielded bands; C. krusei cells produced 55 kDa and C. glabrata 70 kDa bands at both pHs. Moreover, C. glabrata gave another band of 20 kDa at pH 4.0. The media fraction at pH 7.6 and the cell fraction at both pH values tested of C. tropicalis yielded a 70 kDa band. Additionally, another 30 kDa band was observed at pH 4.0.

Conclusions: The results confirmed our study hypothesis. Differences in protease expression seemed to depend on incubation pH. Acidic incubation yielded more bands in gelatin-zymography suggesting that low pH may activate certain proteases of the different Candida strains. This may play a role in promoting gelatinolysis in acidic or basic microniches.