Abstract
Production of ethanol by the yeast Saccharomyces cerevisiae is a process of global importance. In these processes, productivities and yields are pushed to their maximum possible values leading to cellular stress. Transient and lasting enhancements in tolerance and performance have been obtained by genetic engineering, forced evolution, and exposure to moderate levels of chemical and/or physical stimuli, yet the drawbacks of these methods include cost, and multi-step, complex and lengthy treatment protocols. Here, plasma agitation is shown to rapidly induce desirable phenotypic changes in S. cerevisiae after a single treatment, resulting in improved conversion of glucose to ethanol. With a complex environment rich in energetic electrons, highly-reactive chemical species, photons, and gas flow effects, plasma treatment simultaneously mimics exposure to multiple environmental stressors. A single treatment of up to 10 minutes performed using an atmospheric pressure plasma jet was sufficient to induce changes in cell membrane structure, and increased hexokinase 2 activity and secondary metabolite production. These results suggest that plasma treatment is a promising strategy that can contribute to improving metabolic activity in industrial microbial strains, and thus the practicality and economics of industrial fermentations.
Highlights
To ensure long-term survival, organisms have evolved the ability to rapidly adapt to a wide range of highly variable environmental conditions[1,2,3]
The fermentation was analysed for metabolites and enzyme activity (Fig. 1). This strategy was designed to evaluate whole of population phenotypic changes that resulted from plasma treatment of the colony rather than any single cell specific genetic changes
This work demonstrated that plasma agitation has the capacity to rapidly induce desirable metabolic changes in S. cerevisiae after a single brief treatment, leading to enhanced metabolic activity and, as a consequence, a faster and more efficient conversion of glucose to ethanol as well as higher secondary metabolite yields
Summary
To ensure long-term survival, organisms have evolved the ability to rapidly adapt to a wide range of highly variable environmental conditions[1,2,3]. Tolerance to extreme environmental conditions is acquired by means of protective biochemical processes which include the synthesis of osmolytes (e.g. glycerol), trehalose, heat shock proteins (HSPs), increased chaperone activity, enhanced radical oxygen scavenging, changes in redox control, increased proton pumping activity, adjustments in carbon/nitrogen balance and altered ion and water uptake[6,23,24,25,26,27] These response mechanisms initiate the repair of macromolecular damage caused by an environmental factor but presumably establish a tolerant state, which helps prevent further damage. Pre-treatment of yeast cells with a mild osmotic shock conferred increased resistance to heat shock[35,36] and the exposure of yeast to ethanol, sorbic acid and low external pH induced greater thermo-tolerance[37,38] This phenomenon of cross-protection is consistent with commonality in the yeast cellular responses and protection to different forms of environmental damage
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