A microbubble-sparged yeast propagation-fermentation process for bioethanol production.

Area of Science:

• Industrial biotechnology
• Bioprocess engineering
• Microbial physiology

Background:

• Aeration costs in aerobic bioprocesses can reach 15% of production expenses.
• Microbubbles (MBs) offer energy-efficient aeration, potentially reducing costs.
• The physiological impact of MBs on microbial cultures remains largely uncharacterized.

Purpose of the Study:

• To investigate the effects of MB-based aeration on *Saccharomyces cerevisiae* propagation for bioethanol production.
• To compare MB-propagated yeast performance against conventional regular bubble (RB) propagation.
• To analyze gene expression changes in yeast exposed to MBs.

Main Methods:

• Laboratory-scale bioethanol process using MB-based propagation of *Saccharomyces cerevisiae*.
• Comparison of O2 transfer, ethanol titers, and yields between MB and RB propagation.
• Transcript profiling to identify gene expression alterations.

Main Results:

• MB aeration enhanced O2 transfer during yeast propagation.
• Bioethanol titers and yields were similar for MB- and RB-propagated yeast.
• MB propagation led to significant gene expression changes, including upregulated ergosterol biosynthesis genes, but did not improve fermentation performance.

Conclusions:

• Yeast propagated using MB technology demonstrate comparable performance in bioethanol fermentation to conventionally propagated yeast.
• MB-based technology is a viable, energy-efficient alternative for commercial yeast propagation.
• Further research into MBs' physiological effects could optimize bioprocesses.