Exploring xylose metabolism in non-conventional yeasts: kinetic characterization and product accumulation under different aeration conditions

Abstract

d-Xylose is a metabolizable carbon source for several non-Saccharomyces species, but not for native strains of S. cerevisiae. For the potential application of xylose-assimilating yeasts in biotechnological processes, a deeper understanding of pentose catabolism is needed. This work aimed to investigate the traits behind xylose utilization in diverse yeast species. The performance of 9 selected xylose-metabolizing yeast strains was evaluated and compared across 3 oxygenation conditions. Oxygenation diversely impacted growth, xylose consumption, and product accumulation. Xylose utilization by ethanol-producing species such as Spathaspora passalidarum and Scheffersomyces stipitis was less affected by oxygen restriction compared with other xylitol-accumulating species such as Meyerozyma guilliermondii, Naganishia liquefaciens, and Yamadazyma sp., for which increased aeration stimulated xylose assimilation considerably. Spathaspora passalidarum exhibited superior conversion of xylose to ethanol and showed the fastest growth and xylose consumption in all 3 conditions. By performing assays under identical conditions for all selected yeasts, we minimize bias in comparisons, providing valuable insight into xylose metabolism and facilitating the development of robust bioprocesses.

One-sentence summary: This work aims to expand the knowledge of xylose utilization in different yeast species, with a focus on how oxygenation impacts xylose assimilation.

Keywords: Bioethanol; Kinetic characterization; Xylitol; Xylose utilization, Non-conventional yeasts.

Graphical Abstract

Fig. 1.

Variation of the parameters total biomass production (a), maximum specific growth rate (b), net xylose consumption (c) ,and maximum xylose consumption rate (d) under different fermentation conditions. Overall effect on the performance of the yeast species on xylose of the three types of reactor design: aerated reactors, 40% headspace (HS),and 70% HS. The data set includes the nine species of yeast that were evaluated.

Fig. 2.

Biomass growth profile on xylose of the nine species considered (a–i) under the three cultivation conditions. Optical density at 600 nm was monitored over time in aerated reactors (triangle) and in non-aerated reactors with 70% (square) and with 40% headspace (circle).

Fig. 3.

Xylose consumption profile of the nine yeast species considered (a–i). Xylose concentration was monitored over time during the three different cultivation conditions. Aerated reactors (triangle) and non-aerated reactors with 70% (square) and 40% headspace (circle).

Fig. 4.

Ethanol production from xylose over time of the best xylose-fermenting yeast species in non-aerated reactors with 70% and 40% headspace. Scheffersomyces stipitis (a), Spathaspora passalidarum (b), Saccharomyces cerevisiae TMB3400 (c), and Pachysolen tannophilus (d) exhibited the highest ethanol titers and productivities among the nine xylose utilizers strains studied.

Fig. 5.

Phylogenetic tree of xylose-consuming yeasts. Evolutionary analysis was based on the DNA sequences of internal transcribed spacer (ITS)/D1-D2 (a) and the amino acid sequences of xylose reductase (XR) (b) and xylose dehydrogenase (XDH) (c) enzymes. Bootstrap values obtained from 1,000 repetitions are indicated on all branches. Rhizopus arrhizus was selected as the outgroup.