Isolation, characterization, and identification of wild killer yeasts from sugarcane juice

Resumo

Ethanol produced by the fermentation of sugarcane juice has emerged as an important renewable fuel. The yield of this fermentation is affected by undesirable microbial contaminants, but killer yeasts can be a promising strategy to reduce this problem. The present study aimed to isolate, characterize, and identify wild killer yeasts from sugarcane juice. Samples were inoculated in culture medium containing chloramphenicol, and 140 colonies with different characteristics were selected. These isolates were submitted to the killer phenotype assay, and the positive killers were characterized and identified according to the standard methods. Only two strains showed killer activity, identified as Pichia anomala CE025 and P. membranaefaciens CE088. At 25°C, both strains exhibited killer activity at pH 4.0, 4.3, and 4.5, but this activity was not detected at pH 3.0, 3.5, 5.0, and 6.0. The killer phenotype of P. membranaefaciens CE088 was inhibited above 30°C, while for P. anomala, CE025 inhibition occurred only at a higher temperature. Both strains were able to grow in 12% ethanol, and P. anomala CE025 was more tolerant than P. membranaefaciens CE 088. Further studies will be conducted to isolate, purify and identify the killer toxins produced by Pichia anomala and Pichia membranaefaciens species.