Effect of Calcofluor white and Congo red on fungal cell wall morphogenesis: in vivo activation of chitin polymerization.

Calcofluor White (a fluorochrome dye) affected the growth of Geotrichum lactis by causing lysis of cells at the hyphal tips. This effect was prevented by the presence of an osmotic stabilizer. The growth of Saccharomyces cerevisiae was also affected, and multicellular aggregates were formed because of incomplete separation of mother and daughter cells; fluorescence microscopy indicated the presence of abnormally thick septa. The formation of rudimentary wall material by G. lactis protoplasts was promoted by Calcofluor or Congo red (another dye). The rate of chitin synthesis in protoplasts and growing cells was enhanced by both dyes. In contrast, both dyes inhibited chitin and beta (1,3)-glucan synthases in isolated cell-free systems. Degradation rates for beta (1,3)-glucan or chitin were not affected significantly by the dyes. Wheat germ agglutinin also affected chitin synthesis in protoplasts.