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Expression of Mitochondrial Cytochrome C Oxidase Chaperone Gene (COX20) Improves Tolerance to Weak Acid and Oxidative Stress during Yeast Fermentation.

Kumar V, Hart AJ, Keerthiraju ER, Waldron PR, Tucker GA, Greetham D - PLoS ONE (2015)

Bottom Line: Saccharomyces cerevisiae is the micro-organism of choice for the conversion of fermentable sugars released by the pre-treatment of lignocellulosic material into bioethanol.Pre-treatment of lignocellulosic material releases acetic acid and previous work identified a cytochrome oxidase chaperone gene (COX20) which was significantly up-regulated in yeast cells in the presence of acetic acid.This is a study which has utilised tetracycline-regulated protein expression in a fermentation system, which was characterised by improved (or enhanced) tolerance to acetic acid and oxidative stress.

View Article: PubMed Central - PubMed

Affiliation: University of Nottingham, School of Biosciences, Sutton Bonington Campus, Loughborough, LE12 5RD, United Kingdom.

ABSTRACT

Introduction: Saccharomyces cerevisiae is the micro-organism of choice for the conversion of fermentable sugars released by the pre-treatment of lignocellulosic material into bioethanol. Pre-treatment of lignocellulosic material releases acetic acid and previous work identified a cytochrome oxidase chaperone gene (COX20) which was significantly up-regulated in yeast cells in the presence of acetic acid.

Results: A Δcox20 strain was sensitive to the presence of acetic acid compared with the background strain. Overexpressing COX20 using a tetracycline-regulatable expression vector system in a Δcox20 strain, resulted in tolerance to the presence of acetic acid and tolerance could be ablated with addition of tetracycline. Assays also revealed that overexpression improved tolerance to the presence of hydrogen peroxide-induced oxidative stress.

Conclusion: This is a study which has utilised tetracycline-regulated protein expression in a fermentation system, which was characterised by improved (or enhanced) tolerance to acetic acid and oxidative stress.

No MeSH data available.


Related in: MedlinePlus

(A) Glucose utilisation (g/L) during a fermentation for a Δcox20 (pCM173) and Δcox20 (pCM173(COX20)) under control and in the presence of 75 mM acetic acid, (B) ethanol production (g/L) during a fermentation for a Δcox20 (pCM173) and Δcox20 (pCM173(COX20)) under control and in the presence of 75 mM acetic acid.Results presented are a representative of triplicate values (Mean +/- SD n = 3).
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pone.0139129.g005: (A) Glucose utilisation (g/L) during a fermentation for a Δcox20 (pCM173) and Δcox20 (pCM173(COX20)) under control and in the presence of 75 mM acetic acid, (B) ethanol production (g/L) during a fermentation for a Δcox20 (pCM173) and Δcox20 (pCM173(COX20)) under control and in the presence of 75 mM acetic acid.Results presented are a representative of triplicate values (Mean +/- SD n = 3).

Mentions: The fermentation outputs of the two strains under control and 75 mM acetic acid stress were also assessed in terms of glucose utilisation and ethanol production (Fig 5). Under control conditions, it was observed that there was no difference in glucose utilisation or ethanol production between the strains with either the empty vector or pCM173(COX20) (p = 0.861) (Fig 5A and 5B). Addition of 75 mM acetic acid significantly reduced glucose utilisation and ethanol production in the empty vector control strain as compared to the strain overexpressing COX20 (p = 0.0168) (Fig 5A and 5B). This data were used to assess the efficiency of the conversion of glucose into ethanol. Under control conditions, the empty vector Δcox20 control strain had 0.48 ± 0.011 g ethanol/g glucose conversion efficiency, and the pCM173(COX20) strain had an efficiency of 0.49 ± 0.007 ethanol/g glucose conversion after 12 hours. In the presence of 75 mM acetic acid, the Δcox20 control strain had a 0.08 ± 0.008 ethanol/g glucose conversion whereas the pCM173(COX20) strain had a 0.49 ± 0.045 ethanol/g glucose conversion. The theoretical maxima is 0.511 g ethanol per g of glucose consumed [21], therefore the pCM173(COX20) strain is converting glucose into ethanol at near theoretical maximum in the presence of 75 mM acetic acid. The impact of pH was measured on pCM173 and pCM173(COX20), selective media was adjusted to a pH analogous to the addition of 25, 50 or 75 mM acetic acid using phosphoric acid and fermentation rates monitored. Presence of acetic acid in a fermentation using either empty vector (pCM173) or (pCM173(COX20)) was unchanged under control conditions or in the presence of acetic acid (S3 Fig). Results revealed that presence of COX20 had no discernible effect on tolerance to pH when compared with the empty vector (pCM173) control (data not shown).


Expression of Mitochondrial Cytochrome C Oxidase Chaperone Gene (COX20) Improves Tolerance to Weak Acid and Oxidative Stress during Yeast Fermentation.

Kumar V, Hart AJ, Keerthiraju ER, Waldron PR, Tucker GA, Greetham D - PLoS ONE (2015)

(A) Glucose utilisation (g/L) during a fermentation for a Δcox20 (pCM173) and Δcox20 (pCM173(COX20)) under control and in the presence of 75 mM acetic acid, (B) ethanol production (g/L) during a fermentation for a Δcox20 (pCM173) and Δcox20 (pCM173(COX20)) under control and in the presence of 75 mM acetic acid.Results presented are a representative of triplicate values (Mean +/- SD n = 3).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4591339&req=5

pone.0139129.g005: (A) Glucose utilisation (g/L) during a fermentation for a Δcox20 (pCM173) and Δcox20 (pCM173(COX20)) under control and in the presence of 75 mM acetic acid, (B) ethanol production (g/L) during a fermentation for a Δcox20 (pCM173) and Δcox20 (pCM173(COX20)) under control and in the presence of 75 mM acetic acid.Results presented are a representative of triplicate values (Mean +/- SD n = 3).
Mentions: The fermentation outputs of the two strains under control and 75 mM acetic acid stress were also assessed in terms of glucose utilisation and ethanol production (Fig 5). Under control conditions, it was observed that there was no difference in glucose utilisation or ethanol production between the strains with either the empty vector or pCM173(COX20) (p = 0.861) (Fig 5A and 5B). Addition of 75 mM acetic acid significantly reduced glucose utilisation and ethanol production in the empty vector control strain as compared to the strain overexpressing COX20 (p = 0.0168) (Fig 5A and 5B). This data were used to assess the efficiency of the conversion of glucose into ethanol. Under control conditions, the empty vector Δcox20 control strain had 0.48 ± 0.011 g ethanol/g glucose conversion efficiency, and the pCM173(COX20) strain had an efficiency of 0.49 ± 0.007 ethanol/g glucose conversion after 12 hours. In the presence of 75 mM acetic acid, the Δcox20 control strain had a 0.08 ± 0.008 ethanol/g glucose conversion whereas the pCM173(COX20) strain had a 0.49 ± 0.045 ethanol/g glucose conversion. The theoretical maxima is 0.511 g ethanol per g of glucose consumed [21], therefore the pCM173(COX20) strain is converting glucose into ethanol at near theoretical maximum in the presence of 75 mM acetic acid. The impact of pH was measured on pCM173 and pCM173(COX20), selective media was adjusted to a pH analogous to the addition of 25, 50 or 75 mM acetic acid using phosphoric acid and fermentation rates monitored. Presence of acetic acid in a fermentation using either empty vector (pCM173) or (pCM173(COX20)) was unchanged under control conditions or in the presence of acetic acid (S3 Fig). Results revealed that presence of COX20 had no discernible effect on tolerance to pH when compared with the empty vector (pCM173) control (data not shown).

Bottom Line: Saccharomyces cerevisiae is the micro-organism of choice for the conversion of fermentable sugars released by the pre-treatment of lignocellulosic material into bioethanol.Pre-treatment of lignocellulosic material releases acetic acid and previous work identified a cytochrome oxidase chaperone gene (COX20) which was significantly up-regulated in yeast cells in the presence of acetic acid.This is a study which has utilised tetracycline-regulated protein expression in a fermentation system, which was characterised by improved (or enhanced) tolerance to acetic acid and oxidative stress.

View Article: PubMed Central - PubMed

Affiliation: University of Nottingham, School of Biosciences, Sutton Bonington Campus, Loughborough, LE12 5RD, United Kingdom.

ABSTRACT

Introduction: Saccharomyces cerevisiae is the micro-organism of choice for the conversion of fermentable sugars released by the pre-treatment of lignocellulosic material into bioethanol. Pre-treatment of lignocellulosic material releases acetic acid and previous work identified a cytochrome oxidase chaperone gene (COX20) which was significantly up-regulated in yeast cells in the presence of acetic acid.

Results: A Δcox20 strain was sensitive to the presence of acetic acid compared with the background strain. Overexpressing COX20 using a tetracycline-regulatable expression vector system in a Δcox20 strain, resulted in tolerance to the presence of acetic acid and tolerance could be ablated with addition of tetracycline. Assays also revealed that overexpression improved tolerance to the presence of hydrogen peroxide-induced oxidative stress.

Conclusion: This is a study which has utilised tetracycline-regulated protein expression in a fermentation system, which was characterised by improved (or enhanced) tolerance to acetic acid and oxidative stress.

No MeSH data available.


Related in: MedlinePlus