Serum-induced hypha formation in the dimorphic yeast Yarrowia lipolytica

The dimorphic yeast Yarrowia lipolytica forms true hyphae in a medium conta ining N-acetylglucosamine. We made a new finding that serum is a very effec tive inducer of hypha formation of Y. lipolytica: serum induced its hyphal growth very quickly compared to N-acetylglucosamine (4 h vs. 10 h). Osmotic and oxidative stresses (0.2 M NaCl and 20 mM H2O2) inhibited the hypha for mation induced by N-acetylglucosamine. but did not suppress the hypha forma tion triggered by serum. Serum-specific morphological mutants, which formed hyphae in the N-acetylglucosamine medium but not in serum medium, could be isolated. These results suggest that the signal triggered by serum may be transduced through a different pathway, at least in part, from that used fo r the N-acetylglucosamine signal in Y. lipolytica. (C) 2000 Federation of E uropean Microbiological Societies. Published by Elsevier Science B.V. All r ights reserved.