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Xylan-hydrolyzing thermotolerant Candida tropicalis HNMA-1 for bioethanol production from sugarcane bagasse hydrolysate

Nouri, Hoda, Azin, Mehrdad, Mousavi, Mir Latif
Annals of microbiology 2017 v.67 no.9 pp. 633-641
Candida tropicalis, ethanol, ethanol fermentation, ethanol production, heat tolerance, hydrolysates, sugarcane bagasse, temperature, xylan, xylanases, xylose
Sugarcane bagasse is one of the low-cost substrates used for bioethanol production. In order to solubilize sugars in hemicelluloses like xylan, a new thermotolerant isolate of Candida tropicalis HNMA-1 with xylan-hydrolyzing ability was identified and characterized. The strain showed relative tolerance to high temperature. Our results demonstrated 0.211 IU ml⁻¹ xylanase activity at 40 °C compared to 0.236 IU ml⁻¹ at 30 °C. The effect of high temperature on the growth and fermentation of xylose and sugarcane bagasse hydrolysate were also investigated. In both xylose or hydrolysate medium, increased growth was recorded at 40 °C. Meanwhile, the efficiency of ethanol fermentation was adversely affected by temperature since yields of 0.088 g g⁻¹ and 0.076 g g⁻¹ in the xylose medium, in addition to 0.090 g g⁻¹ and 0.078 g g⁻¹ in the hydrolysate medium were noticed at 30 °C and 40 °C, respectively. Inhibitory compounds in the hydrolysate medium demonstrated negative effects on fermentation and productivity, with maximum ethanol concentration attained after 48 h in the hydrolysate, as opposed to 24 h in the xylose medium. Our data show that the newly thermotolerant isolate, C. tropicalis HNMA-1, is able to efficiently ferment xylose and hydrolysate, and also has the capacity for application in ethanol production from hemicellulosic sources.