Deletion of the NOT4 gene impairs hyphal development and pathogenicity in Candida albicans

The Candida albicans NOT4 gene was disrupted in order to investigate the role of Not4p in growth, morphogenesis and pathogenicity. Heterozygote (NOT4/not4), null (not4/not4) and reconstructed heterozygote ([NOT4]/not4) strains of C. albicans, as well as CAF2-1, the parental strain, were grown under conditions that promote hyphal formation. When cultured in liquid medium 199 the heterozygote, reconstructed and wild-type strains began the yeast-to-hyphal transition within 3 h and continued hyphal growth for the duration of experiments. The null mutant also began hyphal growth within 3-5 h but hyphae tended to be shorter and distorted. Subsequently, hyphal growth was arrested and growth returned predominantly to the yeast form. Similar differences were observed when strains were grown on solid Spider medium and medium 199. The parental, heterozygote and reconstructed strains formed normal filamentous networks emanating from colonies. In contrast, the null mutant failed to form hyphae on all solid media tested. The ability of the NOT4 null strain to form biofilms was also investigated, and it was observed that biofilm development does not readily occur for this strain. Virulence of each strain was examined utilizing the mouse model of systemic candidiasis. Mice infected with CAF2-1 succumbed to infection within 3-7 days. All mice infected with the null strain survived for the duration of experiments, while the heterozygote and reconstructed heterozygote strains showed an intermediate level of virulence. These findings suggest that NOT4 may play a role in affecting strain pathogenicity, possibly by regulating expression of certain genes that effect cellular morphogenesis and virulence.