Abstract

The present study describes the isolation of the novel strain Candida intermedia CBS 141442 and investigates the potential of this microorganism for the conversion of lignocellulosic streams. Different C. intermedia clones were isolated during an adaptive laboratory evolution experiment under the selection pressure of lignocellulosic hydrolysate and in strong competition with industrial, xylose-fermenting Saccharomyces cerevisiae cells. Isolates showed different but stable colony and cell morphologies when growing in a solid agar medium (smooth, intermediate and complex morphology) and liquid medium (unicellular, aggregates and pseudohyphal morphology). Clones of the same morphology showed similar fermentation patterns, and the C. intermedia clone I5 (CBS 141442) was selected for further testing due to its superior capacity for xylose consumption (90% of the initial xylose concentration within 72 h) and the highest ethanol yields (0.25 ± 0.02 g ethanol/g sugars consumed). Compared to the well-known yeast Scheffersomyces stipitis, the selected strain showed slightly higher tolerance to the lignocellulosic-derived inhibitors when fermenting a wheat straw hydrolysate. Furthermore, its higher glucose consumption rates (compared to S. stipitis) and its capacity for glucose and xylose co-fermentation makes C. intermedia CBS 141442 an attractive microorganism for the conversion of lignocellulosic substrates, as demonstrated in simultaneous saccharification and fermentation processes.

Highlights

  • Bioethanol is currently the most widely used liquid biofuel

  • We describe the isolation and characterization of 18 C. intermedia clones exhibiting three different cell morphologies from a coculture of S. cerevisiae growing in a medium containing lignocellulosic hydrolysate

  • The results presented demonstrate the potential of C. intermedia as a glucose/xylose cofermentative microorganism for bioethanol production from lignocellulosic feedstocks

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Summary

Introduction

In 2017, the total global bioethanol production was 85 billion L [1], most of which was made from conventional feedstocks such as corn, grain or sugarcane. These sugar- and starch-rich feedstocks are expensive and their use competes with the food and feed sector. Lignocellulosic biomass offers a cheap and attractive alternative due to its availability, a high carbohydrate content (up to 75% of the total dry weight), and the lack of competition with the food and feed sector [2]. Substantial technological development is needed to increase the economic competitiveness of this process

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