Exploring grape marc as trove for new thermotolerant and inhibitor-tolerant Saccharomyces cerevisiae strains for second-generation bioethanol production

Abstract

Background: Robust yeasts with high inhibitor, temperature, and osmotic tolerance remain a crucial requirement for the sustainable production of lignocellulosic bioethanol. These stress factors are known to severely hinder culture growth and fermentation performance. Results: Grape marc was selected as an extreme environment to search for innately robust yeasts because of its limited nutrients, exposure to solar radiation, temperature fluctuations, weak acid and ethanol content. Forty newly isolated Saccharomyces cerevisiae strains gave high ethanol yields at 40°C when inoculated in minimal media at high sugar concentrations of up to 200 g/l glucose. In addition, the isolates displayed distinct inhibitor tolerance in defined broth supplemented with increasing levels of single inhibitors or with a cocktail containing several inhibitory compounds. Both the fermentation ability and inhibitor resistance of these strains were greater than those of established industrial and commercial S. cerevisiae yeasts used as control strains in this study. Liquor from steam-pretreated sugarcane bagasse was used as a key selective condition during the isolation of robust yeasts for industrial ethanol production, thus simulating the industrial environment. The isolate Fm17 produced the highest ethanol concentration (43.4 g/l) from the hydrolysate, despite relatively high concentrations of weak acids, furans, and phenolics. This strain also exhibited a significantly greater conversion rate of inhibitory furaldehydes compared with the reference strain S. cerevisiae 27P. To our knowledge, this is the first report describing a strain of S. cerevisiae able to produce an ethanol yield equal to 89% of theoretical maximum yield in the presence of high concentrations of inhibitors from sugarcane bagasse. Conclusions: This study showed that yeasts with high tolerance to multiple stress factors can be obtained from unconventional ecological niches. Grape marc appeared to be an unexplored and promising substrate for the isolation of S. cerevisiae strains showing enhanced inhibitor, temperature, and osmotic tolerance compared with established industrial strains. This integrated approach of selecting multiple resistant yeasts from a single source demonstrates the potential of obtaining yeasts that are able to withstand a number of fermentation-related stresses. The yeast strains isolated and selected in this study represent strong candidates for bioethanol production from lignocellulosic hydrolysates.

Improving polyhydroxyalkanoate production from inexpensive carbon sources by genetic approaches: a review

“…The biotechnological production of biofuels, biopolymers, and a range of fine chemicals requires significant implementation of biorefinery plants for the conversion of lignocellulosic and cellulosic waste to starting materials . Indeed, lignocellulosic materials consisting of lignin, cellulose, and hemicellulose fibers are acknowledged as the most abundant renewable resources…”

“…The biotechnological production of biofuels, biopolymers, and a range of fine chemicals requires significant implementation of biorefinery plants for the conversion of lignocellulosic and cellulosic waste to starting materials. [111][112][113] Indeed, lignocellulosic materials consisting of lignin, cellulose, and hemicellulose fibers are acknowledged as the most abundant renewable resources. 114 The recalcitrance of lignocellulosic materials to the pre-treatments needed to obtain fermentable hexoses and pentoses represents the major obstacle to PHA production.…”

Utilisation of wheat bran as a substrate for bioethanol production using recombinant cellulases and amylolytic yeast

“…However, the limitations associated with lignocellulosic ethanol production include the slow rate of enzymatic degradation, high enzyme cost and the requirement of inhibitor-tolerant industrial yeast strains [2][3][4]. Consequently, starch is still the most commonly used feedstock for ethanol production, with a relatively mature technology developed for corn in the USA [5] that produced about 52.5 billion litres of bioethanol in 2012, an increase from 49.2 billion litres in 2010 [6].…”

Preliminary physiological characteristics of thermotolerant Saccharomyces cerevisiae clinical isolates identified by molecular biology techniques

“…; Sanchez and Cardona ; Favaro et al . ), as well as for beverages industry (Osho ; Dung et al . ; Nevoigt ).…”

“…In this field of research, the new strains of the yeast with physiological and metabolic special features are very required, especially to grow and efficiently produce valuable metabolites at elevated temperatures. For industrial purpose, the yeast Saccharomyces cerevisiae is the most commonly used micro-organism with a good growth rate for biomass and bioethanol production (Hahn-Hagerdal et al 2006;Sanchez and Cardona 2008;Favaro et al 2013), as well as for beverages industry (Osho 2005;Dung et al 2006;Nevoigt 2008). From thermodynamic point of view, fermentation at elevated temperature allows a higher growth rate and productivity, and economically is profitable because of lowering costs for bioreactors cooling.…”