Abstract
BackgroundLignocellulosic hydrolysates contain a mixture of hexose (C6)/pentose (C5) sugars and pretreatment-generated inhibitors (furans, weak acids and phenolics). Therefore, robust yeast isolates with characteristics of C6/C5 fermentation and tolerance to pretreatment-derived inhibitors are pre-requisite for efficient lignocellulosic material based biorefineries. Moreover, use of thermotolerant yeast isolates will further reduce cooling cost, contamination during fermentation, and required for developing simultaneous saccharification and fermentation (SSF), simultaneous saccharification and co-fermentation (SScF), and consolidated bio-processing (CBP) strategies.ResultsIn this study, we evaluated thirty-five yeast isolates (belonging to six genera including Saccharomyces, Kluyveromyces, Candida, Scheffersomyces, Ogatea and Wickerhamomyces) for pretreatment-generated inhibitors {furfural, 5-hydroxymethyl furfural (5-HMF) and acetic acid} and thermotolerant phenotypes along with the fermentation performances at 40 °C. Among them, a sugarcane distillery waste isolate, Saccharomyces cerevisiae NGY10 produced maximum 49.77 ± 0.34 g/l and 46.81 ± 21.98 g/l ethanol with the efficiency of 97.39% and 93.54% at 30 °C and 40 °C, respectively, in 24 h using glucose as a carbon source. Furthermore, isolate NGY10 produced 12.25 ± 0.09 g/l and 7.18 ± 0.14 g/l of ethanol with 92.81% and 91.58% efficiency via SHF, and 30.22 g/l and 25.77 g/l ethanol with 86.43% and 73.29% efficiency via SSF using acid- and alkali-pretreated rice straw as carbon sources, respectively, at 40 °C. In addition, isolate NGY10 also produced 92.31 ± 3.39 g/l (11.7% v/v) and 33.66 ± 1.04 g/l (4.26% v/v) ethanol at 40 °C with the yields of 81.49% and 73.87% in the presence of 30% w/v glucose or 4× concentrated acid-pretreated rice straw hydrolysate, respectively. Moreover, isolate NGY10 displayed furfural- (1.5 g/l), 5-HMF (3.0 g/l), acetic acid- (0.2% v/v) and ethanol-(10.0% v/v) tolerant phenotypes.ConclusionA sugarcane distillery waste isolate NGY10 demonstrated high potential for ethanol production, C5 metabolic engineering and developing strategies for SSF, SScF and CBP.
Highlights
Lignocellulosic hydrolysates contain a mixture of hexose (C6)/pentose (C5) sugars and pretreatmentgenerated inhibitors
Isolation and molecular characterization of yeast isolates More than 500 microbial colonies showing yeast-like growth were isolated from serial dilutions (10−1–10−6) of six different samples ("Methods"). 82 yeast looking colonies of 10−3 and 10−4 dilutions were further screened on chrome agar [29]
Based on the chrome agar screening and growth at 40 °C, 25 yeast-like colonies were selected to evaluate their fermentation potential related to lignocellulosic ethanol production
Summary
Lignocellulosic hydrolysates contain a mixture of hexose (C6)/pentose (C5) sugars and pretreatmentgenerated inhibitors (furans, weak acids and phenolics). Use of thermotolerant yeast isolates will further reduce cooling cost, contamination during fermentation, and required for developing simultaneous saccharification and fermentation (SSF), simultaneous saccharification and co-fermentation (SScF), and consolidated bio-processing (CBP) strategies. India generates about 650 million metric tons of lignocellulosic waste annually through routine agricultural activities, favored their optimum exploitation as a low-cost renewable carbon source for biofuel production [5,6,7]. Lignocellulosic biomass to ethanol conversion requires three separate processes such as pretreatment, saccharification and fermentation [8, 9]. These separate processes increase the cost of lignocellulosic ethanol production as compared to the first-generation biofuel, wherein pretreatment and saccharification are not required. The major constraint of SSF is the misalliance of thermal optima of enzymatic saccharification (~ 45–50 °C) and fermentation (~ 30 °C) [1]; an intermediate temperature of ~ 40 °C for SSF is suggested to meet the thermal alliance of saccharification and fermentation process [11, 13,14,15]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
