Morphophysiological and molecular characterization of wild yeast isolates from industrial ethanol process

Wild yeasts are commonly found during the fermentation process, displaying different survival and competition strategies that commonly enable their successful spread in the medium. Identifying these yeasts by biological and molecular monitoring, and knowing their traits is vital for the fermentation yield, and this can be done by simple methods such as differential mediaplating, growth rate evaluation and DNA sequencing. The aim of this work was to perform morphophysiological and molecular characterization of 14 yeast isolates from a bioethanol plant in the State of Sao Paulo, Brazil. This was done by employing different culture media to assess the growth and the morphophysiological characteristics of the isolates. The molecular characterization was also done in order to identify the samples in intra-specific levels, compared to the reference strains. The Saccharomyces cerevisiae CAT-1 and PE-2, Brazil’s two main commercial strains, were used as reference. The results suggest that a single ethanol-producing unit may display a highly diversified microbiome, with the occurrence of distinctive wild yeast strains disclosing diverse morphophysiological traits, as observed in the differential media plating and growth rate assay results. The molecular characterization shows that these yeast isolates differ from the reference strains, as observed in interdelta-based PCR fingerprint banding patterns. These findings are a statement of the yeast diversity found in the fermentation process, and are of interest for the ethanol industry, being that many of the commercial strains were firstly isolated from the local biome. Key words: Bioethanol, differential media, growth rate, molecular characterization, morphology, Non-Saccharomyces, Saccharomyces cerevisiae.