Industrial robust yeast isolates with great potential for fermentation of lignocellulosic biomass

Abstract

The search of robust microorganisms is essential to design sustainable processes of second generation bioethanol. Yeast strains isolated from industrial environments are generally recognised to present an increased stress tolerance but no specific information is available on their tolerance towards inhibitors that come from the pretreatment of lignocellulosic materials. In this work, a strategy for the selection of different yeasts using hydrothermal hydrolysate from Eucalyptus globulus wood, containing different concentrations of inhibitors, was developed. Ten Saccharomyces cerevisiae and four Kluyveromyces marxianus strains isolated from industrial environments and four laboratory background strains were evaluated. Interestingly, a correlation between final ethanol titer and percentage of furfural detoxification was observed. The results presented here highlight industrial distillery environments as a remarkable source of efficient yeast strains for lignocellulosic fermentation processes. Selected strains were able to resourcefully degrade furfural and HMF inhibitors, producing 0.8g ethanol/Lh corresponding to 94% of the theoretical yield.

Effect of lignocellulose-derived inhibitors on the growth and d-lactic acid production of Sporolactobacillus inulinus YBS1-5

“…Acetate inhibited the growth of ethanologenic E. coli LY01 by about 35 % when the fermentation medium contained 8.0 g/L acetate [16]. The addition of 3 g/L acetic acid negatively affected all the fermentation parameters of S. cerevisiae [10]. On the other hand, some microorganisms were not inhibited by the high concentration of acetate.…”

“…The order of its inhibitory strength was as follows: syringaldehyde[vanillin[furfural[HMF. Some microorganisms including C. beijerinckii, S. cerevisiae and Rhodococcus species were mainly inhibited by phenolics [10,33]. However, furfural had a more significant effect on ethanol fermentation by P. stipitis than the other inhibitors [21].…”

“…E. coli has a maximum tolerance of 3 g/ L, but growth and ethanol production start being affected at concentrations above 1 g/L [11]. Other microorganisms, including S. cerevisiae, T. thermosaccharolyticum and P. stipitis, have been observed to be almost completely inhibited by furfural and HMF at concentrations of 2-4 g/L [10,26,28]. In this study, compared to acetate, furfural and HMF exerted a negative effect on cell growth and DLA production of S. inulinus YBS1-5 (Fig.…”

“…Up to 5 g/L, S. inulinus YBS1-5 retained 78.6 % of cell growth and 82.5 % of DLA production. From literature data, the tolerance of S. inulinus YBS1-5 toward furfural and HMF was higher than that of most other strains, such as P. stipitis, S. cerevisiae and T. thermosaccharolyticum [10,26,28]. We further investigated the capacity of the YBS1-5 strain to metabolize furfural and HMF (Fig.…”

“…According to Almeida and Jin [6,7], the presence of these byproducts is one of the major challenges in lignocellulose biotransformation. Extensive studies have been recently conducted on analyzing the negative effects of these byproducts on Zymomonas mobilis, Escherichia coli, Saccharomyces cerevisiae and Clostridium beijerinckii for ethanol and butanol production [8][9][10][11]. Sporolactobacillus inulinus is one of the main DLA producers [12].…”