The yeasts of the genus Spathaspora: potential candidates for second‐generation biofuel production

Abstract

Yeasts of the Spathaspora clade have the ability to convert d-xylose to ethanol and/or xylitol. This is an important trait, as these yeasts may be used to produce bioethanol from lignocellulosic biomass or as a source of new d-xylose metabolism genes for recombinant industrial strains of Saccharomyces cerevisiae. The core group of the genus Spathaspora has 22 species, both formally described and not yet described. Other species, such as Sp. allomyrinae, Candida alai, C. insectamans, C. lyxosophila, C. sake, Sp. boniae and C. subhashii are weakly associated with this clade, based on LSU rRNA gene D1/D2 sequence analyses. Spathaspora passalidarum, Sp. arborariae, Sp. gorwiae and Sp. hagerdaliae produce mostly ethanol from d-xylose, whereas the remaining species within the Spathaspora clade already tested for this property may be considered xylitol producers. Among the d-xylose-fermenting Spathaspora species, Sp. passalidarum is the best ethanol producer, displaying high ethanol yields and productivities when cultured in media supplemented with this pentose under oxygen-limited or anaerobic conditions. The species also exhibits rapid d-xylose consumption and the ability to ferment glucose, xylose and cellobiose simultaneously. These characteristics suggest that Sp. passalidarum is a potential candidate for domestication and use in the fermentation of lignocellulosic materials. Copyright © 2017 John Wiley & Sons, Ltd.

The Xylose Metabolizing Yeast Spathaspora passalidarum is a Promising Genetic Treasure for Improving Bioethanol Production

“…Recently, a new xylose-fermenting yeast Spathaspora passalidarum was discovered, which naturally co-ferments xylose, glucose, and cellobiose and demonstrates potentials in the effective conversion of mixed sugars from hemicellulosic hydrolysates into ethanol [9]. S. passalidarum was initially isolated from extremely O 2 -limited and hemicellulosic sugar rich environments from the gut of a wood-boring beetle (as will be discussed below).…”

“…Although the anaerobic fermentation of glucose is broadly known, the xylose fermentation typically needs a controlled oxygen condition. Uncontrolled oxygen conditions in another xylose-fermenting yeast, such as P. stipitis, leads to accumulation of xylitol due to insufficient amounts of NAD + , and as consequence the xylose metabolism will be blocked ( Figure 2) [9,13,14]. To solve this problem, precise controlled O 2 (very low O 2 concentrations) during the xylose fermentation is required in P. stipitis to generate NAD + from NADH.…”

“…The major barrier for cellulose utilization is enzymatic saccharification, while for hemicellulose it is the utilization of mixed sugars (hexose sugars: glucose, galactose, mannose, and rhamnose; and pentose sugars: xylose and arabinose) in the presence of ferulic and acetic acids along with other byproducts of the thermochemical pretreatment of the hydrolysates [13,14]. However, S. passalidarum and P. stipitis yeasts possess a set of unique physiological merits that make them very useful biodegradable organisms for bioconversion of lignocellulosic biomass [4,9,13,14]. Pichia can utilize and ferment effectively cellobiose, glucose, galactose, and mannose along with xylan high oligomeric sugars xylan and mannan, in addition to its extensively studied ability to metabolize and ferment the xylose [4,13,14].…”

“…The primary sugar released in enzymatic hydrolysis is cellobiose and, remarkably, P. stipitis and S. passalidarum have the capability to utilize the cellobiose, which make such yeasts potent organisms for simultaneous saccharification and fermentation (SSF) or hydrolysate, because most commercially available cellulase products are often deficient in β-glucosidase enzyme so the accumulation of cellobiose inhibits cellulose activities. Since P. stipitis and S. passalidarum can directly metabolize the cellobiose, they have the potential to improve SSF processes [4,9,10,13,14,19,20].…”

Ethanol from Biomass Hydrolysates by Efficient Fermentation of Glucose and Xylose – A Review

“…Hagerdaliae ), with Sp. passalidarum being the best ethanol producer from pentoses under oxygen‐limited or anaerobic conditions . Most of xylose‐fermenting microorganisms, such as P. stipitis , require microaerobic conditions for ethanol production.…”