COS1, A 2-COMPONENT HISTIDINE KINASE THAT IS INVOLVED IN HYPHAL DEVELOPMENT IN THE OPPORTUNISTIC PATHOGEN CANDIDA-ALBICANS

Two-component histidine kinases recently have been found in eukaryotic organisms including fungi, slime molds, and plants. We describe the i dentification of a gene, COS1, from the opportunistic pathogen Candida albicans by using a PCR-based screening strategy, The sequence of COS 1 indicates that it encodes a homolog of the histidine kinase Nik-1 fr om the filamentous fungus Neurospora crassa. COS1 is also identical to a gene called CaNIK1 identified in C. albicans by low stringency hybr idization using CaSLN1 as a probe [Nagahashi, S., Mio, T., Yamada-Okab e, T., Arisawa, M., Bussey, H. & Yamada-Okabe, H. (1998) Microbiol. 44 , 425-432]. We assess the function of COS1/CaNIK1 by constructing a di ploid deletion mutant. Mutants lacking both copies of COS1 appear norm al when grown as yeast cells; however, they exhibit defective hyphal f ormation when placed on solid agar media, either in response to nutrie nt deprivation or serum. In constrast to the Delta nik-1 mutant, the D elta cos1/cos1 mutant does not demonstrate deleterious effects when gr own in media of high osmolarity; howe, er both Delta nik-1 and Delta c os1/Delta cos1 mutants show defective hyphal formation. Thus, as predi cted for Nik-1, Cos1p may be involved in some aspect of hyphal morphog enesis and may play a role in virulence properties of the organism.