Submitted to: Applied Microbiology and Biotechnology
Publication Type: Review Article
Publication Acceptance Date: July 9, 2006
Publication Date: December 29, 2006
Citation: Liu, Z. 2006. Genomic adaptation of ethanologenic yeast to biomass conversion inhibitors. Applied Microbiology and Biotechnology. 73(1):27-36.
Interpretive Summary: As interest in alternative energy sources rises, the concept of agriculture as an energy producer has become increasingly attractive. Renewable biomass, including lignocellulosic materials and agricultural residues, has become attractive as potential low-cost materials for bioethanol production. One major barrier of biomass conversion to ethanol is inhibitory compounds generated during biomass pretreatment, which interfere with microbial growth and subsequent fermentation. This study presented a concept of adaptation of ethanologenic yeast to biomass conversion inhibitors using experimental evidence and genomic observations. The concept is also supported by evidence obtained from other systems including dynamic expression for wine fermentation, adaptive mechanism of industrial yeast, and tolerance to toxicity of oxygen in bacterial systems. The author explained a basis of the adaptation concept and the use of functional genomics. As a part of functional genomic approach, multidisciplinary study is also emphasized, such as computation network analysis. This study impacts the biomass-to-ethanol industry, specifically in improvement of tolerance and biotransformation of ethanologenic yeast for biomass conversion to ethanol applications; it also provides an infant genomic basis for theory of biological development.
One major barrier to the economic conversion of biomass to ethanol is inhibitory compounds generated during biomass pretreatment using dilute acid hydrolysis. Major inhibitors such as furfural and 5-hydroxymethylfurfural (HMF) inhibit yeast growth and subsequent fermentation. The ethanologenic yeast Saccharomyces cerevisiae demonstrated a dose-dependant inhibition by the inhibitors, and has potential to transform furfural and HMF into less toxic compounds of furfuryl alcohol and 2,5-bis-hydroxymethylfuran (also termed as furan-2,5-dimethanl, FDM), respectively. For a sustainable and cost-competitive biomass-to-ethanol industry, it is important to develop more tolerant yeast strains that can in situ detoxify the inhibitors and produce ethanol. This study summarizes current knowledge and our understanding of the inhibitors furfural and HMF, discusses metabolic conversion pathways of the inhibitors and the yeast genomic expression response to inhibitor stress. Unlike laboratory strains, gene expression response of the ethanologenic yeast to furfural and HMF was not transient, but a continued dynamic process involving multiple genes at the genome level. This suggests that during the lag phase, ethanologenic yeasts undergo a genomic adaptation process in response to the inhibitors. The findings to date provide a strong foundation for future studies on genomic adaptation and manipulation of yeast to aid more robust strain design and development.