Abstract
BackgroundBiofuels offer a viable alternative to petroleum-based fuel. However, current methods are not sufficient and the technology required in order to use lignocellulosic biomass as a fermentation substrate faces several challenges. One challenge is the need for a robust fermentative microorganism that can tolerate the inhibitors present during lignocellulosic fermentation. These inhibitors include the furan aldehyde, furfural, which is released as a byproduct of pentose dehydration during the weak acid pretreatment of lignocellulose. In order to survive in the presence of furfural, yeast cells need not only to reduce furfural to the less toxic furan methanol, but also to protect themselves and repair any damage caused by the furfural. Since furfural tolerance in yeast requires a functional pentose phosphate pathway (PPP), and the PPP is associated with reactive oxygen species (ROS) tolerance, we decided to investigate whether or not furfural induces ROS and its related cellular damage in yeast.ResultsWe demonstrated that furfural induces the accumulation of ROS in Saccharomyces cerevisiae. In addition, furfural was shown to cause cellular damage that is consistent with ROS accumulation in cells which includes damage to mitochondria and vacuole membranes, the actin cytoskeleton and nuclear chromatin. The furfural-induced damage is less severe when yeast are grown in a furfural concentration (25 mM) that allows for eventual growth after an extended lag compared to a concentration of furfural (50 mM) that prevents growth.ConclusionThese data suggest that when yeast cells encounter the inhibitor furfural, they not only need to reduce furfural into furan methanol but also to protect themselves from the cellular effects of furfural and repair any damage caused. The reduced cellular damage seen at 25 mM furfural compared to 50 mM furfural may be linked to the observation that at 25 mM furfural yeast were able to exit the furfural-induced lag phase and resume growth. Understanding the cellular effects of furfural will help direct future strain development to engineer strains capable of tolerating or remediating ROS and the effects of ROS.
Highlights
Biofuels offer a viable alternative to petroleum-based fuel
Cells exposed to 50 mM furfural had an aggregated staining pattern, which is strikingly different from the even distribution of fluorescence seen when cells are exposed to 25 mM furfural or 5 mM hydrogen peroxide
Cellular damages determined by transmission electron microscopy (TEM) analysis reactive oxygen species (ROS) are known to damage DNA, proteins, lipids, and the cytoskeleton [17,18,19]
Summary
Biofuels offer a viable alternative to petroleum-based fuel. current methods are not sufficient and the technology required in order to use lignocellulosic biomass as a fermentation substrate faces several challenges. The continued use of fossil fuels has raised environmental, economical and political concerns and, as a result, research into improving alternative and renewable energy strategies is of great importance. Bioethanol is one such alternative energy source. Starch and sugar cane sources are currently being used to produce competitively priced ethanol in countries such as Brazil, Canada and the USA. These sources are not sufficient to supply the world bioenergy needs due to the role they play in human and livestock consumption [1]. Programs using agricultural and softwood biomass are currently producing ethanol in Sweden, the USA and Canada, with the later having established a committed plant for the production of bioethanol from lignocellulose [2,3,4]
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