Phenotypic and genotypic identification of yeasts isolated from some dairy products

Abstract

Yeast classification is traditionally based on their physiological and biochemical profiles. Recently, molecular methods have been successfully applied to yeast strain typing and identification. The aim of this paper was to characterize four yeast strains isolated from dairy products by classical and molecular methods. The preliminary examination involved macroscopic appearances of colonies on solid media and microscopic feature of the cells. Physiological characterization was mainly performed by assessing the ability to use certain sugars semi-anaerobically, the ability to use organic compounds as sole carbon source for aerobic growth, urea hydrolysis, growth at high concentrations of glucose and the ability to growth at non-optimal temperatures (37°C and 42°C). From results obtained it could be stated that, although there were some variations in biochemical patterns all tested yeasts were classified either as S. cerevisiae or and G. candidum with 95 – 99 % of probability. For molecular identification only three specific primer pairs and one universal primer were used. The identification was carried out based on ITS 1 partial sequence, 5.8 S rRNA gene and ITS 2 complete sequence and large subunit rRNA gene sequence analysis. The results obtained showed that the product of S. cerevisiae scored 600 bp in lan (1and 2) using 5.8 S rRNA gene with primer ITS and NL2, while G. candidum scored 600 bp in lan (3and 4) using 18S rDNA gene with primer (18S ITS1 – 28S ITS 2). However, the sequence analysis of the four identified yeast strains was submitted to Genebank in the NCBI database. They have been accepted to be deposited and released in Genebank under four new accession numbers, actually KY441458, MF380234 for S. cerevisiae and MF383376, MF383368 for G. candidum strains. In conclusion, Strains were locally isolated from Egyptian resources to increase the additive value of the Egyptian microbial wealth.