Candida albicans mutants in the BNI4 gene have reduced cell-wall chitin and alterations in morphogenesis

The Candida albicans BNI4 gene was identified by homology to the Saccharomyces cerevisiae orthologue and encodes a predicted 1655 amino acid protein. In S. cerevisiae most cell-wall chitin is associated with primary septum formation and Bni4p is involved in tethering the Chs3p chitin synthase enzyme to the mother-bud neck by forming a bridge between a regulatory protein Chs4p and the septin Cdc10p. CaBni4p shows 20 % overall identity to the ScBni4p, with 73 % identity over the C-terminal 63 amino acids, which includes a putative protein phosphatase type 1 (PP1) binding domain. Northern blot analysis revealed a transcript of the expected size that was expressed in both yeast and hyphal growth forms. C. albicans has more chitin in its cell wall than S. cerevisiae, and again most chitin is synthesized by CaChs3p. The function of CaBNI4 was investigated by performing a targeted gene disruption using the 'Ura-blaster' method to delete amino acids 1120-1611 that are essential for function. The resulting Cabni4Delta/Cabni4Delta null mutants formed lemon-shaped yeast cells and had a 30 % reduction in cell-wall chitin, reduced hyphal formation on solid serum-containing medium and increased sensitivity to SDS and increased resistance to Calcofluor White. The Cabni4Delta/Cabni4Delta null mutants were unaffected in chitin ring formation, but often exhibited displaced bud sites with more obvious but flattened birth scars. Therefore, unlike in S. cerevisiae, the Cabni4 mutant apparently alters chitin distribution throughout the cell wall and not exclusively at the bud-neck region.