HMF and furfural stress results in drainage of redox and energy charge of Saccharomyces cerevisiae

Other conference contribution, 2012

Bioethanol produced from lignocellulosic raw materials is a promising alternative to fossil fuels and to decrease greenhouse gas emissions, but several challenges still exist. When lignocellulosic biomass is pretreated, a number of undesired degradation products are generated which may act inhibitory on microbial metabolism. Cellular damage response and repair come at an energy cost for the cell, which could be reflected by alterations in (energy) metabolism. The furaldehydes HMF and furfural have received increasing attention recently. They are formed during pretreatment from dehydration of hexoses and pentoses, respectively. In the present study, the effects of HMF and furfural on redox metabolism, energy metabolism and transcriptome were investigated. Anaerobic chemostat cultivations were performed with the xylose-utilizing Saccharomyces cerevisiae strain VTT C-10883 with both glucose and xylose as carbon sources. By quantifying the redox cofactors NAD(P)+ and NAD(P)H, the catabolic and anabolic reduction charges could be calculated. It was found that both reduction charges were significantly decreased in the presence of HMF and furfural, showing that HMF and furfural are draining the cells of reductive power. Furthermore, the [ATP]/[ADP] ratio of stressed cells was found to be lower than for non-stressed cells, suggesting that the energy metabolism was affected. Transcriptome analysis revealed that genes involved in xenobiotic transporter activity were significantly enriched among the up-regulated genes. The results from the present study provide valuable insights of how Saccharomyces cerevisiae deals with stress imposed by HMF and furfural, which potentially can result in strategies to improve stress tolerance.