Producing alcohol and salt stress tolerant strain of Saccharomyces cerevisiae by heterologous expression of pprI gene

Abstract

Introduction: Ethanol is considered a comparatively clean biofuel, and its large scale production has been a long time concern. Saccharomyces cerevisiae has proven to be the suitable microorganism for large scale ethanol production, but production of other alcohols like butanol and using lignocellulosic substrates is restricted due to lacking tolerance toward toxicity of alcohols, and compounds released from substrates. This study aimed to produce a tolerant strain by using pprI gene of Deinococcus radiodurans.

Material and method: pprI gene was introduced into Saccharomyces cerevisiae. To evaluate the recombinant gene expression, the qPCR was performed. By Gas chromatography, the yield of ethanol production was measured. To estimate the yield of ethanol production each strain was normally cultured in a treated lignocellulosic substrate. The S. cerevisiaes tolerance toward increased salt, ethanol, and butanol concentrations was checked.

Results: Recombinant yeasts tolerated up to 1.2 M salt (7%) and grew well, while normal strain could only survive under 0.85 M (5%) salt concentration. At 5%, 7.5%, 8.5%, 9.5% and 11% ethanol concentrations (v/v), normal cells growth stopped at 7.5% and above; whereas, mutant strains tolerated up to 11% ethanol and proliferated. The mutant yeast's capability to grow in 0.5% and 1% v/v of butanol was raised by 3 and 2.25 fold.

Conclusion: Expression of pprI in different cells increases the tolerance toward various compounds including ethanol, salt and butanol along with boosted yield of biofuel production from ligonocellulosic substrate. Mutant strains showed a higher capability of producing alcohol, and cellular tolerance was raised toward growth restricting compounds released from substrates.

Keywords: Biofuel; Deinococcus radiodurans; Saccharomyces cerevisiae; pprI gene.