In recent years, many novel xylose-fermenting yeasts belonging to the new genus Spathaspora have been isolated from the gut of wood-feeding insects and/or wood-decaying substrates. We have cloned and expressed, in Saccharomyces cerevisiae, a Spathaspora arborariae xylose reductase gene (SaXYL1) that accepts both NADH and NADPH as co-substrates, as well as a Spathaspora passalidarum NADPH-dependent xylose reductase (SpXYL1.1 gene) and the SpXYL2.2 gene encoding for a NAD⁺-dependent xylitol dehydrogenase. These enzymes were co-expressed in a S. cerevisiae strain over-expressing the native XKS1 gene encoding xylulokinase, as well as being deleted in the alkaline phosphatase encoded by the PHO13 gene. The S. cerevisiae strains expressing the Spathaspora enzymes consumed xylose, and xylitol was the major fermentation product. Higher specific growth rates, xylose consumption and xylitol volumetric productivities were obtained by the co-expression of the SaXYL1 and SpXYL2.2 genes, when compared with the co-expression of the NADPH-dependent SpXYL1.1 xylose reductase. During glucose-xylose co-fermentation by the strain with co-expression of the SaXYL1 and SpXYL2.2 genes, both ethanol and xylitol were produced efficiently. Our results open up the possibility of using the advantageous Saccharomyces yeasts for xylitol production, a commodity with wide commercial applications in pharmaceuticals, nutraceuticals, food and beverage industries.

Childhood malnutrition affects physiology and development. It increases infection rates, which may not present clinical signs in severe cases. The World Health Organization recommends prophylactic treatment with cotrimoxazole (SXT) and nutritional recovery to overcome this issue. This treatment is controversial, since evidence of a reduction in morbidity and mortality is not a consensus and could induce the development of antibiotic-resistant bacteria. Moreover, the impact of using this wide-spectrum antibiotic on gut microbiota in a critical period of development, and weakness is unknown. To understand how SXT prophylaxis could affect gut microbiota in undernutrition, we induced protein–energy undernutrition (PEU) in weaning C57BL/6 mice for three weeks and treated animals with SXT for two weeks. Using 16S rRNA gene sequencing, we compared the taxonomic composition and metabolic pathways of control mice, animals submitted to undernutrition (UND), treated with SXT, or undernourished and SXT treated (UND + SXT). We identified that UND mice had a significant increase in predicted pathways related to metabolic syndromes later in life. The prophylactic SXT treatment alone resulted in a significant loss in community richness and beta diversity. Furthermore, we identified the reduction of three genera in SXT treated mice, including the butyrate producers Faecalibacterium and Anaerotruncus. Both UND and double challenge (UND + SXT) resulted in a reduction of the amino acid’s biosynthesis pathway related to cell growth. Our results show that the SXT prophylaxis of young mice during an undernourishment period did not re-establish the undernourished microbiota community composition similar to healthy controls but induced a distinct dysbiotic profile with functional metabolic consequences.