Journal
BIOTECHNOLOGY FOR BIOFUELS
Volume 13, Issue 1, Pages -Publisher
BMC
DOI: 10.1186/s13068-020-01745-5
Keywords
Bioethanol; Conventional bubbles; Ergosterol; Fed-batch fermentation; Microbubbles; Oxygen
Funding
- Innovate UK [102502]
- Innovate UK (EPSRC) [EP/N011511/1]
- BBSRC [BB/N01037X/1] Funding Source: UKRI
- EPSRC [EP/M028127/1, EP/I019790/1, EP/N011511/1] Funding Source: UKRI
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Background Industrial biotechnology will play an increasing role in creating a more sustainable global economy. For conventional aerobic bioprocesses supplying O-2 can account for 15% of total production costs. Microbubbles (MBs) are micron-sized bubbles that are widely used in industry and medical imaging. Using a fluidic oscillator to generate energy-efficient MBs has the potential to decrease the costs associated with aeration. However, little is understood about the effect of MBs on microbial physiology. To address this gap, a laboratory-scale MB-based Saccharomyces cerevisiae Ethanol Red propagation-fermentation bioethanol process was developed and analysed. Results Aeration with MBs increased O-2 transfer to the propagation cultures. Titres and yields of bioethanol in subsequent anaerobic fermentations were comparable for MB-propagated and conventional, regular bubble (RB)-propagated yeast. However, transcript profiling showed significant changes in gene expression in the MB-propagated yeast compared to those propagated using RB. These changes included up-regulation of genes required for ergosterol biosynthesis. Ergosterol contributes to ethanol tolerance, and so the performance of MB-propagated yeast in fed-batch fermentations sparged with 1% O-2 as either RBs or MBs were tested. The MB-sparged yeast retained higher levels of ergosteryl esters during the fermentation phase, but this did not result in enhanced viability or ethanol production compared to ungassed or RB-sparged fermentations. Conclusions The performance of yeast propagated using energy-efficient MB technology in bioethanol fermentations is comparable to that of those propagated conventionally. This should underpin the future development of MB-based commercial yeast propagation.
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