title: Co-production of ethanol and squalene using a Saccharomyces cerevisiae ERG1 (squalene epoxidase) mutant and agro-industrial feedstock.
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 tet0 7 -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 tet0 7 -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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Institute of Life Science, College of Medicine, Swansea University, Swansea, Wales SA2 8PP UK.
authors.forename: Claire M
authors.initials: CM
authors.lastname: Hull
authors.affiliation: School of Chemistry, Cardiff University, Cardiff, Wales CF10 3AT UK.
authors.forename: E Joel
authors.initials: EJ
authors.lastname: Loveridge
authors.affiliation: Institute of Life Science, College of Medicine, Swansea University, Swansea, Wales SA2 8PP UK.
authors.forename: Nicola J
authors.initials: NJ
authors.lastname: Rolley
authors.affiliation: Institute of Biological, Environmental & Rural Sciences, Aberystwyth University, Gogerddan, Aberystwyth, Wales SY23 3EE UK.
authors.forename: Iain S
authors.initials: IS
authors.lastname: Donnison
authors.affiliation: Institute of Life Science, College of Medicine, Swansea University, Swansea, Wales SA2 8PP UK.
authors.forename: Steven L
authors.initials: SL
authors.lastname: Kelly
authors.affiliation: Institute of Life Science, College of Medicine, Swansea University, Swansea, Wales SA2 8PP UK.
authors.forename: Diane E
authors.initials: DE
authors.lastname: Kelly
keywords: Bio-based products; ERG1; Ethanol; Squalene; Squalene epoxidase; Sterol