Abstract
Yeast-based bioethanol production from lignocellulosic hydrolysates (LH) is an attractive and sustainable alternative for biofuel production. However, the presence of acetic acid (AA) in LH is still a major problem. Indeed, above certain concentrations, AA inhibits yeast fermentation and triggers a regulated cell death (RCD) process mediated by the mitochondria and vacuole. Understanding the mechanisms involved in AA-induced RCD (AA-RCD) may thus help select robust fermentative yeast strains, providing novel insights to improve lignocellulosic ethanol (LE) production. Herein, we hypothesized that zinc vacuolar transporters are involved in vacuole-mediated AA-RCD, since zinc enhances ethanol production and zinc-dependent catalase and superoxide dismutase protect from AA-RCD. In this work, zinc limitation sensitized wild-type cells to AA-RCD, while zinc supplementation resulted in a small protective effect. Cells lacking the vacuolar zinc transporter Zrt3 were highly resistant to AA-RCD, exhibiting reduced vacuolar dysfunction. Moreover, zrt3Δ cells displayed higher ethanol productivity than their wild-type counterparts, both when cultivated in rich medium with AA (0.29 g L−1 h−1 versus 0.11 g L−1 h−1) and in an LH (0.73 g L−1 h−1 versus 0.55 g L−1 h−1). Overall, the deletion of ZRT3 emerges as a promising strategy to increase strain robustness in LE industrial production.
Highlights
This article is an open access articleLignocellulosic ethanol (LE) has gained increasing public attention as a secondgeneration biofuel
Acetic acid is the main inhibitor of fermentation of lignocellulosic hydrolysates
We aimed to clarify the role of the zinc transporter Zrt3 in the mechanisms underlying acetic acid-induced regulated cell death (RCD) in yeast, towards the improvement of lignocellulosic ethanol (LE) production
Summary
Lignocellulosic ethanol (LE) has gained increasing public attention as a secondgeneration biofuel. It produces less greenhouse gases (GHGs) and can be obtained from inexpensive and abundant agricultural and forestry residues, and its production does not require the food resources that first-generation biofuels do [1,2]. Lignocellulosic hydrolysis-derived inhibitors, such as weak acids (e.g., acetic, formic and levulinic acids), furan aldehydes (e.g., furfural and 5-hydroxymethylfurfural (HMF)), and phenolic compounds, together with increasing concentrations of ethanol along fermentation, cause severe stress that limits ethanol productivity [5,6]. Improving the resistance of yeast cells to such different stresses will boost fermentative efficiency [7] and determine LE production sustainability
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