Role of calcineurin in stress resistance, morphogenesis, and virulence of a Candida albicans wild-type strain

Abstract

By generating a calcineurin mutant of the Candida albicans wild-type strain SC5314 with the help of a new recyclable dominant selection marker, we confirmed that calcineurin mediates tolerance to a variety of stress conditions but is not required for the ability of C. albicans to switch to filamentous growth in response to hypha-inducing environmental signals. While calcineurin was essential for virulence of C. albicans in a mouse model of disseminated candidiasis, deletion of CMP1 did not significantly affect virulence during vaginal or pulmonary infection, demonstrating that the requirement for calcineurin for a successful infection depends on the host niche.

FIG. 1.

Construction of the C. albicans cmp1 deletion mutant and complemented strain. (A) Structure of the CMP1 deletion cassette (top) and genomic structure of the CMP1 locus in the parent strain SC5314 (bottom). The CMP1 coding region is represented by the white arrow, and the upstream and downstream sequences by the solid lines. The direct repeats of the 34-bp FRT site (black arrows) bordering the CdMPA^R flipper cassette are not drawn to scale. The SAP2 promoter (P_SAP2) is indicated by the bent arrow, the caFLP gene by the hatched arrow, the transcription termination sequence of the ACT1 gene (T_ACT1) by the black diamond, and the CdMPA^R marker by the gray arrow. The diagnostic BglII sites are shown, and the DNA fragments used for Southern hybridization analysis of the mutants are indicated by thick bars (probe 1 and probe 2). (B) Structure of the DNA cassette (top) which was used for reintegration of an intact CMP1 copy (white arrow) into one of the inactivated cmp1Δ alleles (bottom). (C) Southern hybridization of BglII-digested genomic DNA of the parent strain SC5314 and mutant derivatives with the CMP1-specific probe 1. The sizes of the hybridizing fragments (in kilobases) are given on the left of the blot, and their identities are indicated on the right.

FIG. 2.

Virulence of the C. albicans cmp1Δ mutant in different infection models. (A and B) Survival of mice after intravenous (A) or intranasal (B) infection with the wild-type parental strain SC5314, the cmp1Δ mutant SCCMP1M4, or the reconstituted strain SCCMP1MK2 (cmp1Δ plus CMP1). (C) Vaginal fungal burden in mice infected intravaginally with the cmp1Δ mutant and control strains was measured by determining the CFU in vaginal lavage fluid at the indicated times.