The role of microfilaments and microtubules during pH-regulated morphological transition in Candida albicans.

Yeast cells of Candida albicans produced germ tubes in a salt-glucose medium containing 4% calf serum at pH 7 and 37 degrees C. Hyphal growth continued for 24 h and the filaments did not revert to yeast cells. When cells were grown at pH 4, reversion to yeast growth was observed, despite the presence of serum. The elongation of hyphae was inhibited within 30 min. The distribution of microtubules and microfilaments during pH-regulated morphological transition was studied by an immunofluorescence technique using an antitubulin antibody with a FITC-conjugated secondary antibody, and by staining with tetramethylrhodaminyl phalloidin for filamentous actin and actin granules. After changing to acidic conditions, microtubules were distributed normally in the cytoplasm; however, microfilaments disappeared from hyphal cells, and actin granules were localized at the site of budding. These results show that microfilaments play an important role during pH-regulated morphological transition.