Mutation in the beta subunit of F ATPase allows Kluyveromyces lactis to survive the disruption of the KlPGS1 gene

Pleiotropic effect of anionic phospholipids absence on mitochondrial morphology and cell wall integrity in strictly aerobic Kluyveromyces lactis yeasts

Cardiolipin and phosphatidylglycerol are anionic phospholipids localized to the inner mitochondrial membrane. In this study, it is demonstrated by fluorescence and transmission electron microscopy that atp2.1pgs1Δ mutant mitochondria lacking anionic phospholipids contain fragmented and swollen mitochondria with a completely disorganized inner membrane. In the second part of this study, it was shown that the temperature sensitivity of the atp2.1pgs1Δ mutant was not suppressed by the osmotic stabilizer glucitol but by glucosamine, a precursor of chitin synthesis. The atp2.1pgs1Δ mutant was hypersensitive to Calcofluor White and caffeine, resistant to Zymolyase, but its sensitivity to caspofungin was the same as the strains with the standard PGS1 gene. The distribution of chitin in the mutant cell wall was impaired. The glucan level in the cell wall of the atp2.1pgs1Δ mutant was reduced by 4-8 %, but the level of chitin was almost double that in the wild-type strain. The cell wall of the atp2.1pgs1Δ mutant was about 20 % thinner than the wild type, but its morphology was not significantly altered.

Absence of anionic phospholipids in Kluyveromyces lactis cells is fatal without F1-catalysed ATP hydrolysis

We have shown in previous research that the loss of phosphatidylglycerol and cardiolipin caused by disruption of the PGS1 gene is lethal for the petite-negative yeast Kluyveromyces lactis . This present study demonstrates the role and mechanism of atp2.1 in the suppression of pgs1 lethality in K. lactis cells. Phenotypic characterization has shown that a strain lacking the phosphatidylglycerolphosphate synthase (atp2.1pgs1Δ) possessed a markedly impaired respiratory chain, very low endogenous respiration, and uncoupled mitochondria. As a result the mutant strain was unable to generate a sufficient mitochondrial membrane potential via respiration. The atp2.1 suppressor mutation enabled an increase in the affinity of F(1)-ATPase for ATP in the hydrolytic reaction, resulting in the maintenance of sufficient membrane potential for the biogenesis of mitochondria and survival of cells lacking anionic phospholipid biosynthesis.