Bioprospecting thermotolerant yeasts from distillery effluent and molasses for high‐temperature ethanol production

Abstract

Aims: Isolation, characterization and assessment of inhibitor tolerance of thermotolerant yeasts associated with distillery effluent and molasses, and their use in hightemperature 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.

Genotypic and Phenotypic Diversity of Kluyveromyces marxianus Isolates Obtained from the Elaboration Process of Two Traditional Mexican Alcoholic Beverages Derived from Agave: Pulque and Henequen (Agave fourcroydes) Mezcal

“…This association with dairy products is due its capability to metabolize lactose. This species has also been isolated from plants such as agave [ 18 ]; fruits such as overripened mango pulp [ 19 ]; vegetables such as rotting onions [ 20 ]; and agro-industrial residues in sugar mills [ 21 ], sugarcane bagasse hydrolysates [ 22 ], blue agave bagasse [ 23 ], coffee wet processing wastewater [ 24 ], and distillery effluents and molasses [ 25 ]. K. marxianus is also part of the microbiota involved in the fermentation of cereal-based African fermented beverages [ 26 ], French cider [ 27 ], Georgian wine [ 28 ], Brazilian cachaça [ 29 ], and Mexican agave-based spirits tequila and mezcal [ 30 , 31 , 32 ].…”

Genotypic and Phenotypic Diversity ofKluyveromyces marxianusIsolates Obtained from the Elaboration Process of Two Traditional Mexican Alcoholic Beverages Derived from Agave: Pulque and Henequen (Agave fourcroydes) Mezcal

“…This association with dairy products is due its capability to metabolize lactose. This species has also been isolated from plants and fruits as, agave [17], rotting onions [18], overripened mango pulp [19] and agro-industrial residues in sugar mills [20], sugarcane bagasse hydrolysates [21], coffee wet processing wastewater [22], blue agave bagasse [23], and distillery effluents and molasses [24]. K. marxianus is also part of the microbiota involved in the fermentation of cereal-based African fermented beverages [25], French cider [26], Georgian wine [27], Brazilian cachaça [28], and Mexican agave-based spirits tequila and mezcal [29][30][31].…”