Co-production of ethanol and squalene using a Saccharomyces cerevisiae ERG1 (squalene epoxidase) mutant and agro-industrial feedstock

Claire Hull, Joel Loveridge, Nicola Rolley, Iain Simon Donnison, Steven Lewis Kelly, Diane Elizabeth Kelly

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23 Citations (SciVal)
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Abstract

Background
Genetically customised Saccharomyces cerevisiae that can produce ethanol and additional bio-based chemicals from sustainable agro-industrial feedstocks (for example, residual plant biomass) are of major interest to the biofuel industry. We investigated the microbial biorefinery concept of ethanol and squalene co-production using S. cerevisiae (strain YUG37-ERG1) wherein ERG1 (squalene epoxidase) transcription is under the control of a doxycycline-repressible tet07-CYC1 promoter. The production of ethanol and squalene by YUG37-ERG1 grown using agriculturally sourced grass juice supplemented with doxycycline was assessed.

Results
Use of the tet07-CYC1 promoter permitted regulation of ERG1 expression and squalene accumulation in YUG37-ERG1, allowing us to circumvent the lethal growth phenotype seen when ERG1 is disrupted completely. In experiments using grass juice feedstock supplemented with 0 to 50 μg doxycycline mL−1, YUG37-ERG1 fermented ethanol (22.5 [±0.5] mg mL−1) and accumulated the highest squalene content (7.89 ± 0.25 mg g−1 dry biomass) and yield (18.0 ± 4.18 mg squalene L−1) with supplements of 5.0 and 0.025 μg doxycycline mL−1, respectively. Grass juice was found to be rich in water-soluble carbohydrates (61.1 [±3.6] mg sugars mL−1) and provided excellent feedstock for growth and fermentation studies using YUG37-ERG1.

Conclusion
Residual plant biomass components from crop production and rotation systems represent possible substrates for microbial fermentation of biofuels and bio-based compounds. This study is the first to utilise S. cerevisiae for the co-production of ethanol and squalene from grass juice. Our findings underscore the value of the biorefinery approach and demonstrate the potential to integrate microbial bioprocess engineering with existing agriculture.
Original languageEnglish
Article number133
Number of pages9
JournalBiotechnology for Biofuels
Volume7
Early online date24 Sept 2014
DOIs
Publication statusPublished - 2014

Keywords

  • Bio-based products
  • Squalene epoxidase
  • Squalene
  • Ethanol
  • Sterol
  • ERG1

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