Screening and regulation of alkaline extracellular protease and ribonuclease production of Yarrowia lipolytica strains isolated and identified from different cheeses in Turkey

In this research, 43 yeast strains were isolated from different types of cheese in Turkey and these isolates were identified with both phenotypic tests and genotypic tests with 5.8S ITS-PCR. Also, the sequence of PCR fragments obtained from ITS-PCR was analyzed by DNA sequencing. In the results of the phenotypic tests, 9 of 43 isolates were identified as Yarrowia lipolytica. After the phenotypic identification, all the isolates were identified with ITS-PCR and 13 were identified as Y. lipolytica. Yarrowia lipolytica secretes several hydrolytic enzymes including alkaline and acid proteases, lipases, a ribonuclease, and phosphotases. In this paper, the effect of carbon and nitrogen sources and pH on production of AEP and RNase were examined for our identified strains of Y. lipolytica. The best production of AEP were found in skim milk medium with pH 7.0 by TEM YL 5 and Y. lipolytica CBS 6124 type strain. An extra carbon source (glucose) reduced AEP production at all the pH studied. Glutamine which is a nitrogen source did not affect AEP production. In contrast to AEP production, glucose increased RNase production at all the pH studied.