Enhanced Tolerance to Antifungals as a General Feature of Rho<sup>−</sup> Mutants in Yeast Species: Implications to Positive Selection of Respiratory Deficiency
Although the mitochondrial genome is an attribute of all eukaryotes, some yeast species (called petite-positive) can replicate without mitochondrial DNA (mtDNA). Strains without mtDNA (known as rho<sup>−</sup> mutants or petite mutants) are respiration-deficient and require fermentable c...
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2025-01-01
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| author | Zachary Johnson Farhan Nadim Mikhajlo K. Zubko |
| author_facet | Zachary Johnson Farhan Nadim Mikhajlo K. Zubko |
| author_sort | Zachary Johnson |
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| description | Although the mitochondrial genome is an attribute of all eukaryotes, some yeast species (called petite-positive) can replicate without mitochondrial DNA (mtDNA). Strains without mtDNA (known as rho<sup>−</sup> mutants or petite mutants) are respiration-deficient and require fermentable carbon sources (such as glucose) for their metabolism. However, they are compromised in many aspects of fitness and competitiveness. Nevertheless, a few research groups have reported that some petite mutants of <i>Candida glabrata</i> and <i>Saccharomyces cerevisiae</i> manifested higher levels of tolerance to the antifungal fluconazole than their wild-type (WT) counterparts. In this study, we show that elevated tolerance to two or three out of four tested antifungals is a generic feature of at least five petite-positive species of yeasts including <i>C. glabrata</i> (higher tolerance of petites to clotrimazole and miconazole), <i>S. bayanus</i> (tolerance to clotrimazole, fluconazole, and miconazole), <i>S. cerevisiae</i> (tolerance to clotrimazole and fluconazole), <i>S. paradoxus</i> (tolerance to clotrimazole, fluconazole, and miconazole), and <i>S. pastorianus</i> (tolerance to clotrimazole and fluconazole). Comparing the levels of tolerance to the antifungals in WT and petite mutants was based on measuring the diameters of the zones of inhibition (ZOIs) using disc diffusion assays. The mode of inhibition in the majority of WT strains by all antifungals was fungicidal; most of the rho<sup>−</sup> mutants manifested fungistatic inhibition. We observed partial (not complete) inhibition in WT, with four different types of ZOI patterns that were species- and antifungal-specific. The partial inhibition was characterised by the presence of antifungal-tolerant colonies within ZOI areas. The inability of these colonies selected from ZOIs to grow on glycerol, as a single source of carbon, proved that they were rho<sup>−</sup> mutants spontaneously generated in the WT populations. The results on the elevated tolerance of petite strains to antifungals are discussed in terms of the prospective positive selection of respiratory-deficient mutants and the various implications of such selection. |
| format | Article |
| id | doaj-art-d6400aa22bf34407959cc575928c6347 |
| institution | Kabale University |
| issn | 2076-2607 |
| language | English |
| publishDate | 2025-01-01 |
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| spelling | doaj-art-d6400aa22bf34407959cc575928c63472025-01-24T13:42:38ZengMDPI AGMicroorganisms2076-26072025-01-011319910.3390/microorganisms13010099Enhanced Tolerance to Antifungals as a General Feature of Rho<sup>−</sup> Mutants in Yeast Species: Implications to Positive Selection of Respiratory DeficiencyZachary Johnson0Farhan Nadim1Mikhajlo K. Zubko2Centre for Bioscience, Manchester Metropolitan University, John Dalton Building, Chester Street, Manchester M1 5GD, UKCentre for Bioscience, Manchester Metropolitan University, John Dalton Building, Chester Street, Manchester M1 5GD, UKCentre for Bioscience, Manchester Metropolitan University, John Dalton Building, Chester Street, Manchester M1 5GD, UKAlthough the mitochondrial genome is an attribute of all eukaryotes, some yeast species (called petite-positive) can replicate without mitochondrial DNA (mtDNA). Strains without mtDNA (known as rho<sup>−</sup> mutants or petite mutants) are respiration-deficient and require fermentable carbon sources (such as glucose) for their metabolism. However, they are compromised in many aspects of fitness and competitiveness. Nevertheless, a few research groups have reported that some petite mutants of <i>Candida glabrata</i> and <i>Saccharomyces cerevisiae</i> manifested higher levels of tolerance to the antifungal fluconazole than their wild-type (WT) counterparts. In this study, we show that elevated tolerance to two or three out of four tested antifungals is a generic feature of at least five petite-positive species of yeasts including <i>C. glabrata</i> (higher tolerance of petites to clotrimazole and miconazole), <i>S. bayanus</i> (tolerance to clotrimazole, fluconazole, and miconazole), <i>S. cerevisiae</i> (tolerance to clotrimazole and fluconazole), <i>S. paradoxus</i> (tolerance to clotrimazole, fluconazole, and miconazole), and <i>S. pastorianus</i> (tolerance to clotrimazole and fluconazole). Comparing the levels of tolerance to the antifungals in WT and petite mutants was based on measuring the diameters of the zones of inhibition (ZOIs) using disc diffusion assays. The mode of inhibition in the majority of WT strains by all antifungals was fungicidal; most of the rho<sup>−</sup> mutants manifested fungistatic inhibition. We observed partial (not complete) inhibition in WT, with four different types of ZOI patterns that were species- and antifungal-specific. The partial inhibition was characterised by the presence of antifungal-tolerant colonies within ZOI areas. The inability of these colonies selected from ZOIs to grow on glycerol, as a single source of carbon, proved that they were rho<sup>−</sup> mutants spontaneously generated in the WT populations. The results on the elevated tolerance of petite strains to antifungals are discussed in terms of the prospective positive selection of respiratory-deficient mutants and the various implications of such selection.https://www.mdpi.com/2076-2607/13/1/99antifungalsazoles<i>Candida</i><i>Saccharomyces</i>rho<sup>−</sup> mutantspetite |
| spellingShingle | Zachary Johnson Farhan Nadim Mikhajlo K. Zubko Enhanced Tolerance to Antifungals as a General Feature of Rho<sup>−</sup> Mutants in Yeast Species: Implications to Positive Selection of Respiratory Deficiency Microorganisms antifungals azoles <i>Candida</i> <i>Saccharomyces</i> rho<sup>−</sup> mutants petite |
| title | Enhanced Tolerance to Antifungals as a General Feature of Rho<sup>−</sup> Mutants in Yeast Species: Implications to Positive Selection of Respiratory Deficiency |
| title_full | Enhanced Tolerance to Antifungals as a General Feature of Rho<sup>−</sup> Mutants in Yeast Species: Implications to Positive Selection of Respiratory Deficiency |
| title_fullStr | Enhanced Tolerance to Antifungals as a General Feature of Rho<sup>−</sup> Mutants in Yeast Species: Implications to Positive Selection of Respiratory Deficiency |
| title_full_unstemmed | Enhanced Tolerance to Antifungals as a General Feature of Rho<sup>−</sup> Mutants in Yeast Species: Implications to Positive Selection of Respiratory Deficiency |
| title_short | Enhanced Tolerance to Antifungals as a General Feature of Rho<sup>−</sup> Mutants in Yeast Species: Implications to Positive Selection of Respiratory Deficiency |
| title_sort | enhanced tolerance to antifungals as a general feature of rho sup sup mutants in yeast species implications to positive selection of respiratory deficiency |
| topic | antifungals azoles <i>Candida</i> <i>Saccharomyces</i> rho<sup>−</sup> mutants petite |
| url | https://www.mdpi.com/2076-2607/13/1/99 |
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