Isolation of thermotolerant xylose-utilizing yeasts for ethanol and xylitol production

Abstract

Aims: The implementation of simultaneous saccharification and co-fermentation (SScF) and consolidated bioprocessing (CBP) is highly anticipated for industrial bioethanol applications. Thus, microorganisms capable of utilizing hexose and pentose sugars, as well as thermotolerant, are considered advantageous for optimum ethanol production. Methodology and results: Thermotolerant yeast strains were isolated from wastewater ponds of ethanol-producing facility as well as empty fruit bunch composting area and screened for xylose-and glucose-fermenting ability. Five out of 24 total isolates were able to grow at 40 C and were found positive for ethanol production from xylose. Based on their high efficiency of xylose and glucose utilization, two isolates were chosen for further characterization. They were identified as Kluyveromyces marxianus UniMAP 1-1 and Schwanniomyces etchellsii UniMAP 1-7 based on the D1/D2 region of the large subunit ribosomal DNA. The growth kinetics of each isolate on xylose and glucose at 40 °C were determined. The two isolates were able to ferment xylose to ethanol at a maximum concentration between 0.533 ± 0.415 and 1.243 ± 0.246 g/L with concomitant xylitol production between 9.932 ± 0.303 and 12.933 ± 0.505 g/L. Fermentation of glucose to ethanol was also tested for these isolates and the yields were and 0.361 and 0.118 g/g for UniMAP 1-1 and UniMAP 1-7, respectively. Conclusion, significance and impact of study: The potential of these thermotolerant microbes to be used for xylitol and bioethanol production from lignocelluloses are evident from this study.