Scientists from Jiangnan University and the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) of Chinese Academy of Sciences have uncovered new insights into the microbial dynamics of high-temperature Daqu fermentation.

Published on December 16 in Bioresource Technology, the study reveals how yeast species collaborate to maintain metabolic activity under extreme fermentation conditions, providing deeper insights into microbial interactions during Daqu production.

The study, led by Prof. XU Yan from Jiangnan University and Prof. XU Jian from QIBEBT, addresses a long-standing challenge in fermentation science. While traditional multi-omics technologies offer a snapshot of microbial composition, they fail to pinpoint which microorganisms are actively involved in fermentation, especially under harsh conditions. This gap has hindered a comprehensive understanding of fermentation mechanisms, particularly in high-temperature environments.

By combining the Ramanomics platform with deuterium oxide (D2O) labeling, the team was able to isolate and identify yeast species that remain metabolically active during the fermentation process. Their findings revealed that only 10–32% of the yeast species detected by sequencing were actually metabolically active under heat stress, challenging the assumption that microbial abundance correlates directly with functional involvement in the fermentation process.

"The ability to track metabolically active yeast at the single-cell level is a breakthrough in understanding how different microorganisms contribute to the fermentation process," said ZHANG Huaizhi, the study's first author from Jiangnan University. "Our findings show that even low-abundance species play a crucial role in maintaining fermentation stability, especially under extreme conditions."

The study also uncovered a dynamic collaboration between various yeast species during fermentation. In the moderate-temperature stages, Saccharomycopsis fibuligera and Wickerhamomyces anomalus were primarily responsible for substrate degradation and flavor precursor production. However, as the temperature exceeded 45°C, Pichia kudriavzevii emerged as the dominant yeast, showing remarkable heat tolerance and continued metabolic activity.

This study is the first to map the temporal partitioning of yeast species in high-temperature fermentation, offering new insights into how low-abundance yet metabolically active species contribute to the overall stability of the process. It also highlights the importance of using single-cell, activity-based techniques to more accurately identify functional microorganisms in complex microbial communities.

“This ability to profile metabolic functions of live yeast cells and sort them directly from the microbiota that produce high-value wine can transform how we monitor fermentation processes and mine microbial cell factories from them” added Prof. XU Jian, who co-led this study from QIBEBT.

By improving the precision of identifying key yeast species in fermentation, this study has the potential to enhance the efficiency of fermentation processes in industries such as food production and bioenergy.

Special Forces of Microbes Found in High-Temperature Daqu

（Text by LIU Yang, Figure by LIU Yang / ZHANG Huaizhi）