Intergeneric yeast fusants with efficient ethanol production from cheese whey powder solution: Construction of a Kluyveromyces marxianus and Saccharomyces cerevisiaeAY‐5 hybrid

Due to its high content of lactose and abundant availability, cheese whey powder ( CWP ) has received much attention for ethanol production in fermentation processes. However, lactose‐fermenting yeast strains including K luyveromyces marxianus can only produce alcohol at a relatively low level, while the most commonly used distiller yeast strain S accharomyces cerevisiae cannot ferment lactose since it lacks both β‐galactosidase and the lactose permease system. To combine the unique aspects of these two yeast strains, hybrids of K . marxianus TY ‐22 and S . cerevisiae AY ‐5 were constructed by protoplast fusion. The fusants were screened and characterized by DNA content, β‐galactosidase activity, ethanol tolerance, and ethanol productivity. Among the genetically stable fusants, the DNA content of strain R ‐1 was 6.94%, close to the sum of the DNA contents of TY ‐22 (3.99%) and AY ‐5 (3.51%). The results obtained by random‐amplified polymorphic DNA analysis suggested that R ‐1 was a fusant between AY ‐5 and TY ‐22. During the fermentation process with CWP , the hybrid strain R ‐1 produced 3.8% v/v ethanol in 72 h, while the parental strain TY ‐22 only produced 3.1% v/v ethanol in 84 h under the same conditions.