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

Authors Organisations
  • Claire Hull(Author)
    Prifysgol Abertawe | Swansea University
  • Joel Loveridge(Author)
    Prifysgol Caerdydd | Cardiff University
  • Nicola Rolley(Author)
    Prifysgol Abertawe | Swansea University
  • Iain Donnison(Author)
  • Steven Lewis Kelly(Author)
    Prifysgol Abertawe | Swansea University
  • Diane Elizabeth Kelly(Author)
    Prifysgol Abertawe | Swansea University
Type Article
Original languageEnglish
Article number133
Number of pages9
JournalBiotechnology for Biofuels
Volume7
Early online date24 Sep 2014
DOI
Publication statusPublished - 2014
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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.

Keywords

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