Control of filament formation in Candida albicans by polyamine levels

Candida albicans, the most common fungal pathogen, regulates its cellular m orphology in response to environmental conditions. The ODC gene, which enco des ornithine decarboxylase, a key enzyme in polyamine biosynthesis, was is olated and disrupted. Homozygous null Candida mutants behaved as polyamine auxotrophs and grew exclusively in the yeast form at low polyamine levels ( 0.01 mM putrescine) under all conditions tested. An increase in the polyami ne concentration (10 mM putrescine) restored the capacity to switch from th e yeast to the filamentous form. The strain with a deletion mutation also s howed increased sensitivity to salts and calcofluor white, This Candida odc /odc mutant was virulent in a mouse model. The results suggest a model in w hich polyamine levels exert a pleiotrophic effect on transcriptional activi ty.