Reexamining the Effects of Media and Selective Pressures in <i>Saccharomyces cerevisiae</i> Isolation from Floral Samples

Background: The yeast Saccharomyces cerevisiae plays a pivotal role in fermentation industries, yet its ecological behavior and methods for effective isolation from natural environments, particularly floral sources, remain insufficiently understood. Conventional enrichment media are often assumed to selectively favor S. cerevisiae, facilitating its dominance during cultivation. Methodology: This study evaluated the effectiveness of several enrichment media based on osmotic pressure tolerance, ethanol resistance, and raffinose utilization, using both batch and chemostat cultivation systems. Camellia flower samples served as the primary isolation source. ITS region sequencing was used for taxonomic identification. We also compared colony recovery through direct streaking versus dilution plating, and attempted S. cerevisiae isolation via pAUR plasmid-based transformation. Results: Contrary to expectations, S. cerevisiae was not dominant in any culture condition. Instead, genera such as Lachancea thermotolerans and Metschnikowia spp. predominated across conditions. Only a single S. cerevisiae isolate was recovered from batch cultures, exclusively through dilution plating. Transformation with pAUR plasmids failed to yield positive isolates, possibly reflecting limited plasmid receptivity in wild strains. Conclusion: These results challenge the effectiveness of traditional media for specifically enriching S. cerevisiae and underscore the importance of dilution plating in recovering rare, non-dominant strains. The findings invite further exploration of ecological and genetic factors affecting wild S. cerevisiae, including their transformation competence.