Yeasts Have Evolved Divergent Enzyme Strategies To Deconstruct and Metabolize Xylan
Journal article, 2023

Together with bacteria and filamentous fungi, yeasts actively take part in the global carbon cycle. Over 100 yeast species have been shown to grow on the major plant polysaccharide xylan, which requires an arsenal of carbohydrate active enzymes. However, which enzymatic strategies yeasts use to deconstruct xylan and what specific biological roles they play in its conversion remain unclear. In fact, genome analyses reveal that many xylan-metabolizing yeasts lack expected xylanolytic enzymes. Guided by bioinformatics, we have here selected three xylan-metabolizing ascomycetous yeasts for in-depth characterization of growth behavior and xylanolytic enzymes. The savanna soil yeast Blastobotrys mokoenaii displays superior growth on xylan thanks to an efficient secreted glycoside hydrolase family 11 (GH11) xylanase; solving its crystal structure revealed a high similarity to xylanases from filamentous fungi. The termite gut-associated Scheffersomyces lignosus, in contrast grows more slowly, and its xylanase activity was found to be mainly cell surface-associated. The wood-isolated Wickerhamomyces canadensis, surprisingly, could not utilize xylan as the sole carbon source without the addition of xylooligosaccharides or exogenous xylanases or even co-culturing with B. mokoenaii, suggesting that W. canadensis relies on initial xylan hydrolysis by neighboring cells. Furthermore, our characterization of a novel W. canadensis GH5 subfamily 49 (GH5_49) xylanase represents the first demonstrated activity in this subfamily. Our collective results provide new information on the variable xylanolytic systems evolved by yeasts and their potential roles in natural carbohydrate conversion. IMPORTANCE Microbes that take part in the degradation of the polysaccharide xylan, the major hemicellulose component in plant biomass, are equipped with specialized enzyme machineries to hydrolyze the polymer into monosaccharides for further metabolism. However, despite being found in virtually every habitat, little is known of how yeasts break down and metabolize xylan and what biological role they may play in its turnover in nature. Here, we have explored the enzymatic xylan deconstruction strategies of three underexplored yeasts from diverse environments, Blastobotrys mokoenaii from soil, Scheffersomyces lignosus from insect guts, and Wickerhamomyces canadensis from trees, and we show that each species has a distinct behavior regarding xylan conversion. These findings may be of high relevance for future design and development of microbial cell factories and biorefineries utilizing renewable plant biomass.

xylanase

microbial co-cultures

CAZymes

yeast

xylan

Author

Jonas Ravn

Chalmers, Life Sciences, Industrial Biotechnology

Amanda Sörensen Ristinmaa

Chalmers, Life Sciences, Industrial Biotechnology

Tom Coleman

Chalmers, Life Sciences, Industrial Biotechnology

Johan Larsbrink

Chalmers, Life Sciences, Industrial Biotechnology

Cecilia Geijer

Chalmers, Life Sciences, Industrial Biotechnology

Microbiology spectrum

2165-0497 (eISSN)

Vol. 11 3 e0024523

Upgrading of cellulose fibers into porous materials.Acronym: BreadCell

European Commission (EC) (EC/H2020/964430), 2021-04-01 -- 2025-03-31.

Subject Categories

Biochemistry and Molecular Biology

Biocatalysis and Enzyme Technology

DOI

10.1128/spectrum.00245-23

PubMed

37098941

More information

Latest update

7/17/2023