Isolation and identification of killer yeasts from Agave sap (aguamiel) and pulque

Wild killer yeasts have been identified as inhibitory to strains used as st arters in the production of alcoholic beverages such as beer and wine; ther efore, killer or killer-resistant strains have been sought for use in alcoh olic fermentations. In the current paper a total of 16 strains belonging to six species were isolated. From two samples of Agave sap (aguamiel) the fo llowing yeast strains were isolated: Candida lusitaneae (1), Kluyveromyces marxianus var. bulgaricus (2), and Saccharomyces cerevisiae (capensis) (1). Additionally, in seven samples of pulque (the fermented product), the spec ies C. valida (six strains), S. cerevisiae (chevalieri) (4), S. cerevisiae (capensis) (1), and K. marxianus var. lactis (1) were found. The killer str ains were C. valida and K. marxianus var. lactis from pulque and K. marxian us var. bulgaricus from aguamiel. One strain of S. cerevisiae (chevalieri) isolated from pulque which did not show killer activity was, on the other h and, resistant to other killer strains and it had a remarkable ethanol tole rance, suggesting that this strain could be used for alcohol production.