Effect of O₂, ergosterol and sterol precursors on the mating ability of Kluyveromyces lactis

It was found that the difference in the partial pressure of oxygen (pO₂) resulting from the distinct altitude over the sea level, between Baltimore, Md., USA and Mexico City, about 2,240 meters, is sufficient to cause variance in conjugation frequency in two haploid strains of Kluyveromyces lactis. Further studies confirm that sexual conjugation in K. lactis is highly sensitive to changes in the pO₂. Ergosterol which depends on O₂ for its biosynthesis, stimulates the mating process, as does the ergosterol precursor, squalene. Ergosterol and O₂ effects were found to be additive, suggesting that O₂ may influence conjugation in more than one way. Culture, storage and transfer frequency modify both, mating efficiency and the response to O₂ and lipid supplement.