Evaluation of divergent yeast genera for fermentation-associated stresses and identification of a robust sugarcane distillery waste isolate Saccharomyces cerevisiae NGY10 for lignocellulosic ethanol production in SHF and SSF

Abstract

Background Lignocellulosic 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. Results In 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. Conclusion A sugarcane distillery waste isolate NGY10 demonstrated high potential for ethanol production, C5 metabolic engineering and developing strategies for SSF, SScF and CBP. Electronic supplementary material The online version of this article (10.1186/s13068-019-1379-x) contains supplementary material, which is available to authorized users.

Harnessing pongamia shell hydrolysate for triacylglycerol agglomeration by novel oleaginous yeast Rhodotorula pacifica INDKK

“…Sugar (glucose, xylose, arabinose) and inhibitor (5-HMF, furfural and acetic acid) concentrations in PSH were determined by using HPLC (Agilent 1260 Series) equipped with Aminex HPX-87H column (Bio-Rad, USA) and refractive index (RI) detector. The mobile phase H 2 SO 4 (4 mM) at a flow rate of 0.3 mL/min at column temperature of 40 °C and the sugar as well as inhibitor were quantified by dividing the peak area of the sample with the peak area of standard (1.0 g/L) at specific retention time [28]. Trace elements were determined by inductively coupled plasma-induced ion chromatography-mass spectroscopy (ICP-MS) analysis (Agilent 7900) using argon as carrier gas and sample flow rate was 2.0 mL/min with approximately 2.5 min total analysis time per sample.…”

“…In this study, we collected a pool of potential oleaginous yeast isolates (57) including strains procured from collection centres in India (NCIM and MTCC) as well as by screening samples from various sites of biomass degradation (Additional file 1: [27]. The evolutionary background of the taxa was determined by the maximum likelihood method [28]. The bootstrap consensus of tree was obtained from 1000 replicates and units of branch length are represented by number of nucleotide substitutions per site.…”

Overcoming lignocellulose‐derived microbial inhibitors: advancing the Saccharomyces cerevisiae resistance toolbox

“…Several natural S. cerevisiae isolates have displayed increased ethanol tolerance and higher ethanol productivity with increased growth, both in the absence and presence of inhibitory compounds, in comparison with laboratory and industrial strains . These natural strains originate from diverse environments including vineyards and industrial waste streams, which allows bioprospecting for new strains with the potential of harboring industrially relevant traits . Bioprospecting for natural S. cerevisiae isolates therefore allows for the elucidation of new, previously unexplored inhibitor resistance mechanisms because natural strains are genetically and phenotypically distinct and display several single nucleotide polymorphisms (SNPs) that may generate rare alleles associated with polymorphisms that bring about phenotype variation .…”

“…Environmental stresses induce modifications of yeast metabolism and physiology, resulting in the adaptation and the development of environment‐specific traits . Coupled with classical breeding, this allows for the generation of hybrid progeny that contain the complete genome of both parental strains, thereby increasing the genetic diversity of the organisms towards enhanced survival phenotypes.…”

Rational Engineering of Saccharomyces Cerevisiae Towards Improved Tolerance to Multiple Inhibitors in Lignocellulose Fermentations

“…Given the toxicity of these compounds, studies have been undertaken to develop yeast strains capable of not only withstanding the harsh conditions associated with lignocellulosic biomass fermentations, but to also generate ethanol yields expected in industrial processes [5,22]. Thus, microbial inhibitor toxicity represents a bottle-neck in lignocellulosic bioethanol production and negating these detrimental inhibitory effects remains to be a fundamental challenge [22,24,25].…”