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JAC Advance Access originally published online on April 21, 2005
Journal of Antimicrobial Chemotherapy 2005 55(6):905-913; doi:10.1093/jac/dki112
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© The Author 2005. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved. For Permissions, please e-mail: journals.permissions{at}oupjournals.org

Squalene epoxidase encoded by ERG1 affects morphogenesis and drug susceptibilities of Candida albicans

Ritu Pasrija1,{dagger}, Shankarling Krishnamurthy2,{dagger},{ddagger}, Tulika Prasad1, Joachim F. Ernst2 and Rajendra Prasad1,*

1 School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India; 2 Institut für Mikrobiologie, Heinrich-Heine-Universität, 40225 Düsseldorf, Germany

* Corresponding author. Tel: +91-11-2670-4509; Fax: +91-11-2671-7081; Email: rp47{at}mail.jnu.ac.in

Objectives: Functional characterization of the erg1 mutant of ergosterol biosynthesis of Candida albicans.

Methods: We disrupted the ERG1 gene of C. albicans, which encodes squalene epoxidase (EC 1.14.99.7). Since the disruption of both alleles of ERG1 was lethal, the second allele of a heterozygous disruptant was placed under the control of a regulable promoter, MET3p, which is repressed by methionine and cysteine.

Results: The reverse-phase HPLC analysis of sterol, extracted from the conditional mutant strain, showed a total lack of ergosterol and instead accumulation of squalene. This imbalance in sterol composition led to defects in growth and increased susceptibilities to drugs including fluconazole, ketoconazole, cycloheximide, nystatin, amphotericin B and terbinafine. Reduced drug efflux activity of the erg1 mutant was associated with poor surface localization of Cdr1p, suggesting that enhanced passive diffusion and reduced efflux mediated by the ABC (ATP binding cassette) transporter Cdr1p increases drug susceptibility. Additionally, conditional erg1 mutant strains were unable to form hyphae in various media.

Conclusions: Taken together, our results demonstrate that the absence of ergosterol, which is one of the constituents of membrane microdomains (rafts), has a direct effect on drug susceptibility and morphogenesis of C. albicans.

Keywords: regulable promoter , hyphae , drug resistance , Cdr1p , ergosterol , dimorphism


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