Purification and characterization of two killer toxins originated from Torulaspora delbrueckii (Lindner) and Wickerhamomyces anomalus (E.C.Hansen) Kurtzman, Robnett, and Basehoar-Powers

Abstract

Abstract Background Ecological killer yeasts have had few studies compared with laboratory killer yeasts. The killer yeasts are known in excreting killer toxins that kill sensitive or susceptible yeasts. The killer toxins, such as TK and WK excreted from two yeast isolates (Torulaspora delbrueckii and Wickerhamomyces anomalus) have protenious nature with different molecular weight depending on yeast species. Results A qualitative test was conducted to determine the ability of both isolates to produce killer toxins on the media of yeast extract and malt extract broth when the two toxins were first purified by ammonium sulfate salt at 40% concentration and then by dialysis for the killer toxin TK and gel filtration method for WK. The molecular weight of TK was estimated at about 15 kDa, while WK was at 45 kDa. The chemical properties of the killer toxins were also studied. The results showed that the two killer toxins were with protenious nature. Conclusion Both yeast isolates (Torulaspora delbrueckii and Wickerhamomyces anomalus) had the ability of producing different kinds of killer toxins. The two killer toxins (TK and WK) were identified for the first time in Iraq, and their production involves many steps of economically unexpansive purification method with a good quality and high purity of producing killer toxins. The results confirmed that the nature of killer toxins (WK and TK) was similar to protein compounds resulted from the transition in UV and functional groups.