A microbubble-sparged yeast propagation\u2013fermentation process for bioethanol production

Vijayendran Raghavendran,Vicki Springthorpe,Robert K Poole,William B Zimmerman,Tony R Larson,Hamza Mohammed,Jeffrey Green,Joseph P Webb,Michaël L Cartron,Michael Hines

doi:10.1186/s13068-020-01745-5

Vijayendran Raghavendran, Vicki Springthorpe + Show 8 more

Open Access

https://doi.org/10.1186/s13068-020-01745-5

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Abstract

BackgroundIndustrial biotechnology will play an increasing role in creating a more sustainable global economy. For conventional aerobic bioprocesses supplying O2 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.ResultsAeration with MBs increased O2 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% O2 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.ConclusionsThe 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.

Highlights

Industrial biotechnology will play an increasing role in creating a more sustainable global economy
A spinning disc MB device was shown to be able to provide cultures of Saccharomyces cerevisiae with adequate O2 at low agitation speed, with consequent savings in energy costs [6]. Some of these savings arise because MBs provide better mixing than regular bubbles (RB), thereby reducing local concentration gradients that could lead to O2-starved zones in large propagators [7]
Construction of a microbubble (MB) fermenter The prototype MB fermenter was constructed by removing the stirrer shaft and sparger from a conventional system (Fig. 1)

Summary

Introduction

Industrial biotechnology will play an increasing role in creating a more sustainable global economy. 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. A spinning disc MB device was shown to be able to provide cultures of Saccharomyces cerevisiae (up to 50 L volume) with adequate O2 at low agitation speed, with consequent savings in energy costs [6]. Some of these savings arise because MBs provide better mixing than regular bubbles (RB), thereby reducing local concentration gradients that could lead to O2-starved zones in large propagators [7].

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