An industrial ethanol-producing Saccharomyces cerevisiae strain with genes of fungal oxido-reductive pathway needed for xylose fermentation integrated into its genome (YRH1415) was used to obtain haploids and diploid isogenic strains. The isogenic strains were more effective in metabolizing xylose than YRH1415 strain and able to co-ferment glucose and xylose in the presence of high concentrations of inhibitors resulting from the hydrolysis of lignocellulosic biomass (switchgrass). The rate of xylose consumption did not appear to be affected by the ploidy of strains or the presence of two copies of the xylose fermentation genes but by heterozygosity of alleles for xylose metabolism in YRH1415. Furthermore, inhibitor tolerance was influenced by the heterozygous genome of the industrial strain, which also showed a marked influenced on tolerance to increasing concentrations of toxic compounds, such as furfural. In this work, selection of haploid derivatives was found to be a useful strategy to develop efficient xylose-fermenting industrial yeast strains.

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Here, we report the draft genome sequence of the yeast Spathaspora xylofermentans UFMG-HMD23.3 (=CBS 12681), a d-xylose-fermenting yeast isolated from the Amazonian forest. The genome consists of 298 contigs, with a total size of 15.1 Mb, including the mitochondrial genome, and 5,948 predicted genes.

Contamination of water by microcystins is a global problem. These potent hepatotoxins demand constant monitoring and control methods in potable water. Promising approaches to reduce contamination risks have focused on natural microcystin biodegradation led by enzymes encoded by the mlrABCD genes. The first enzyme of this system (mlrA) linearizes microcystin structure, reducing toxicity and stability. Heterologous expression of mlrA in different microorganisms may enhance its production and activity, promote additional knowledge on the enzyme, and support feasible applications. In this context, we intended to express the mlrA gene from Sphingosinicella microcystinivorans B9 in an industrial Saccharomyces cerevisiae strain as an innovative biological alternative to degrade microcystins. The mlrA gene was codon-optimized for expression in yeast, and either expressed from a plasmid or through chromosomal integration at the URA3 locus. Recombinant and wild yeasts were cultivated in medium contaminated with microcystins, and the toxin content was analyzed during growth. Whereas no difference in microcystins content was observed in cultivation with the chromosomally integrated strain, the yeast strain hosting the mlrA expression plasmid reduced 83% of toxins within 120 h of cultivation. Our results show microcystinase A expressed by industrial yeast strains as a viable option for practical applications in water treatment.