Expression of mitochondrial cytochrome c oxidase chaperone gene (COX20) improves tolerance to weak acid and oxidative stress during yeast fermentation

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. Pretreatment of lignocellulosic material releases acetic acid and previous work identified a cytochromeoxidase 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. Over expressing COX20 using a tetracycline-regulatable expression vector system in a Δcox20 strain, resulted in tolerance to the presence of acetic acid and tolerance could b eablated with addition of tetracycline. Assays also revealed that overexpression improvedtolerance 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.