Advances and Developments in Strategies to Improve Strains of Saccharomyces cerevisiae and Processes to Obtain the Lignocellulosic Ethanol−A Review

Abstract

The conversion of biomass into ethanol using fast, cheap, and efficient methodologies to disintegrate and hydrolyse the lignocellulosic biomass is the major challenge of the production of the second-generation ethanol. This revision describes the most relevant advances on the conversion process of lignocellulose materials into ethanol, development of new xylose-fermenting strains of Saccharomyces cerevisiae using classical and modern genetic tools and strategies, elucidation of the expression of some complex industrial phenotypes, tolerance mechanisms of S. cerevisiae to lignocellulosic inhibitors, monitoring and strategies to improve fermentation processes. In the last decade, numerous engineered pentose-fermenting yeasts have been developed using molecular biology tools. The increase in the tolerance of S. cerevisiae to inhibitors is still an important issue to be exploited. As the industrial systems of ethanol production operate under non-sterile conditions, microbial subpopulations are generated, depending on the operational conditions and the levels of contaminants. Among the most critical requirements for production of the second-generation ethanol is the reduction in the levels of toxic by-products of the lignocellulosic hydrolysates and the production of low-cost and efficient cellulosic enzymes. A number of procedures have been established for the conversion of lignocellulosic materials into ethanol, but none of them are completely satisfactory when process time, costs, and efficiency are considered.

Harnessing Genetic Diversity in Saccharomyces cerevisiae for Fermentation of Xylose in Hydrolysates of Alkaline Hydrogen Peroxide-Pretreated Biomass

“…Even with the minimal enzymes needed for conversion, xylose fermentation often remains inefficient. In particular, xylose metabolism can be impaired by cofactor imbalance generated with the use of NADPH and NAD ϩ -coupled enzymes (15,16). This imbalance is further exacerbated during anaerobic fermentation during which oxygen is unavailable for respiratory generation the NAD ϩ cofactor for xylitol dehydrogenase activity (17).…”

Roles of the Yap1 Transcription Factor and Antioxidants in Saccharomyces cerevisiae's Tolerance to Furfural and 5-Hydroxymethylfurfural, Which Function as Thiol-Reactive Electrophiles Generating Oxidative Stress

“…However, because of the extremely rigid and complex nature of lignocellulose, pretreatment is required to make this material available for subsequent enzymatic digestion and microbial fermentation (1). The commonly used dilute acid pretreatment generates numerous chemical by-products such as furan aldehydes, weak acids, and phenol derivatives, which inhibit microbial cell growth and ethanol fermentation (2). To overcome the inhibitory effects of these compounds, various physical and chemical methods of medium detoxification have been developed (1).…”

“…To overcome the inhibitory effects of these compounds, various physical and chemical methods of medium detoxification have been developed (1). However, because of the high cost of medium detoxification methods, biodetoxification of inhibitors by using tolerant microorganisms is considered a more practical alternative (2).…”

Identification of auxotrophic mutants of the yeast Kluyveromyces marxianus by non‐homologous end joining‐mediated integrative transformation with genes from Saccharomyces cerevisiae

“…Due to the vast amount of information on the molecular biology and genetics of S. cerevisiae, it is also the first choice for studying eukaryotic systems and fermentation analysis (Coughlan and Brodsky, 2005;Laluce et al, 2012;Lodolo et al, 2008;Mattiazzi et al, 2012;Schuller and Casal, 2005;Smith and Snyder, 2006). To date, numerous excellent methods for genetic manipulations have been developed for S. cerevisiae, making it an ideal model eukaryote for life science and genomic studies.…”