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  • Title: Bioprospecting thermotolerant yeasts from distillery effluent and molasses for high-temperature ethanol production.
    Author: Avchar R, Lanjekar V, Baghela A.
    Journal: J Appl Microbiol; 2022 Feb; 132(2):1134-1151. PubMed ID: 34487585.
    Abstract:
    AIMS: Isolation, characterization and assessment of inhibitor tolerance of thermotolerant yeasts associated with distillery effluent and molasses, and their use in high-temperature ethanol production from alkali-treated rice straw. METHODS AND RESULTS: A total of 92 thermotolerant yeasts were isolated from seven different distillery effluent and molasses samples. Based on MSP-PCR, 34 yeasts were selected and identified by sequencing the D1/D2 domain of LSU rDNA. These yeasts belonged to eight genera and nine different species. We assessed the inhibitor tolerance of these 34 well-characterized yeasts against various pre-treatment-generated inhibitors (furfural, 5-hydroxymethyl furfural and acetic acid) and also evaluated their ethanol yields at 40, 45 and 50℃. Among selected strains, Pichia kudriavzevii DSA3.2 exhibited the highest ethanol production (24.5 g l-1 ) with an efficiency of 95.7% at 40℃ using 5% glucose. At 45℃, P. kudriavzevii DSA3.2 and Kluyveromyces marxianus MSS6.3 yielded maximum ethanol titres; 22.3 and 23 g l-1 with 87.4% and 90% efficiency, respectively. While using alkali-treated RS at 45℃, K. marxianus MSS6.3 produced 10.5 g l-1 of ethanol with 84.5% fermentation efficiency via separate hydrolysis and fermentation, and 10.9 g l-1 of ethanol with 85% efficiency via simultaneous saccharification and fermentation. Pichia kudriavzevii DSA3.2, DSA3.1 and K. marxianus MSS6.3 also exhibited significant tolerance against multiple inhibitors. CONCLUSIONS: Yeast isolates P. kudriavzevii DSA3.2 and K. marxianus MSS6.3 exhibited significant inhibitor tolerance and proved to be suitable for high-temperature ethanol fermentation. After additional optimization and scale-up experiments, these isolates can be exemplary candidates for industrial-scale ethanol production from lignocellulosic biomass. SIGNIFICANCE AND IMPACT OF THE STUDY: Our study recognizes distillery effluents and molasses as specialized niches for yeasts with a broad substrate range, capable of tolerating multiple inhibitors and yielding high levels of ethanol at elevated temperatures. These yeasts can further be exploited for bioethanol production through SSF/SHF at a larger scale.
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