Deletion of the Candida glabrata ERG3 and ERG11 genes: effect on cell viability, cell growth, sterol composition, and antifungal susceptibility.

We have cloned and sequenced the structural genes encoding the delta 5,6 sterol desaturase (ERG3 gene) and the 14 alpha-methyl sterol demethylase (ERG11 gene) from Candida glabrata L5 (leu2). Single and double mutants of these genes were created by gene deletion. The phenotypes of these mutants, including sterol profiles, aerobic viabilities, antifungal susceptibilities, and generation times, were studied. Strain L5D (erg3 delta::LEU2) accumulated mainly ergosta-7,22-dien-3 beta-ol, was aerobically viable, and remained susceptible to antifungal agents but had a slower generation time than its parent strain. L5LUD (LEU2 erg11 delta::URA3) strains required medium supplemented with ergosterol and an anaerobic environment for growth. A spontaneous aerobically viable mutant, L5LUD40R (LEU erg11 delta::URA3), obtained from L5LUD (LEU2 erg11 delta::URA3), was found to accumulate lanosterol and obtusifoliol, was resistant to azole antifungal agents, demonstrated some increase in resistance to amphotericin B, and exhibited a 1.86-fold increase in generation time in comparison with L5 (leu2). The double-deletion mutant L5DUD61 (erg3 delta::LEU2 erg11 delta::URA3) was aerobically viable, produced mainly 14 alpha-methyl fecosterol, and had the same antifungal susceptibility pattern as L5LUD40R (LEU2 erg11 delta::URA3), and its generation time was threefold greater than that of L5 (leu2). Northern (RNA) analysis revealed that the single-deletion mutants had a marked increase in message for the undeleted ERG3 and ERG11 genes. These results indicate that differences in antifungal susceptibilities and the restoration of aerobic viability exist between the C. glabrata ergosterol mutants created in this study and those sterol mutants with similar genetic lesions previously reported for Saccharomyces cerevisiae.