Trehalose hydrolysis is not required for human serum-induced dimorphic transition in Candida albicans: evidence from a tps1/tps1 mutant deficient in trehalose synthesis

Exponential yeast-like cells of a Candida albicans wild-type strain exhibited strong capacity for germ tube formation in a glucose-containing medium (YPD) after induction with human serum at 37 degrees C, whereas the isogenic double disruptant tps1/tps1 mutant, which is deficient in trehalose synthesis, failed to produce germ tubes. In a medium without glucose (YP), the morphological transition fraction was roughly equivalent in both strains. Substitution of glucose by galactose or glycerol increased the number of wild-type proliferating cells able to enter the dimorphic program with no noticeable change in their trehalose content, while stationary cells, which accumulate a large amount of trehalose, did not form germ tubes. When fresh medium was added, a high proportion of these resting cells recovered their ability to carry out dimorphic transition. The tps1/tps1 mutant followed the same pattern of hyphae formation, despite the fact that it was unable to accumulate trehalose either during dimorphism induction or after several stress challenges. Furthermore, trehalose-6-phosphate synthase activity was barely detectable in the mutant. These results strongly suggest that serum-induced dimorphic transition does not require trehalose mobilization; they also support the idea that TPS1 is the only activity involved in trehalose biosynthesis in C. albicans.