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Aquatic Metschnikowia species (M. australis, M. bicuspidata, M. krissii, and M. zobellii) are sensitive to 10 out of 12 mycocins secreted by Pichia membranifaciens strains. Terrestrial species M. pulcherrima and M. reukaufii are resistant to all these mycocins, while M. gruessii and M. lunata are sensitive to one of them. The yeast described as Torula rubifaciens is also sensitive to this mycocin.

The molecular karyotyping analysis of 21 strains within the taxonomic complex Pichia membranifaciens allowed the sibling species P. membranifaciens and P. manshurica, as well as P. deserticola and P. punctispora, to be differentiated. Heterogeneity of the species P. membranifaciens at the variety level is discussed.

Pichia membranifaciensCYC 1086 secretes a killer toxin (PMKT2) that is inhibitory to a variety of spoilage yeasts and fungi of agronomical interest. The killer toxin in the culture supernatant was concentrated by ultrafiltration and purified to homogeneity by two successive steps, including native electrophoresis and HPLC gel filtration. Biochemical characterization of the toxin showed it to be a protein with an apparent molecular mass of 30 kDa and an isoelectric point of 3.7. At pH 4.5, optimal killer activity was observed at temperatures up to 20 °C. Above approximately this pH, activity decreased sharply and was barely noticeable at pH 6. The toxin concentrations present in the supernatant during optimal production conditions exerted a fungicidal effect on a variety of fungal and yeast strains. The results obtained suggest that PMKT2 has different physico-chemical properties from PMKT as well as different potential uses in the biocontrol of spoilage yeasts. PMKT2 was able to inhibitBrettanomyces bruxellensiswhileSaccharomyces cerevisiaewas fully resistant, indicating that PMKT2 could be used in wine fermentations to avoid the development of the spoilage yeast without deleterious effects on the fermentative strain. In small-scale fermentations, PMKT2, as well asP. membranifaciensCYC 1086, was able to inhibitB. bruxellensis, verifying the biocontrol activity of PMKT2 in simulated winemaking conditions.

The use ofPichia membranifaciensCYC 1106 killer toxin againstBotrytis cinereawas investigated. This strain exerted a broad-specificity killing action against other yeasts and fungi. At pH 4, optimal killer activity was observed at temperatures up to 20 °C. At 25 °C the toxic effect was reduced to 70 %. The killer activity was higher in acidic medium. Above about pH 4·5 activity decreased sharply and was barely noticeable at pH 6. The killer toxin protein fromP. membranifaciensCYC 1106 was purified to electrophoretic homogeneity. SDS-PAGE of the purified killer protein indicated an apparent molecular mass of 18 kDa. Killer toxin production was stimulated in the presence of non-ionic detergents. The toxin concentrations present in the supernatant during optimal production conditions exerted a fungicidal effect on a strain ofB. cinerea. The symptoms of infection and grey mould observed inVitis viniferaplants treated withB. cinereawere prevented in the presence of purifiedP. membranifacienskiller toxin. The results obtained suggest thatP. membranifaciensCYC 1106 killer toxin is of potential use in the biocontrol ofB. cinerea.