Ethanol production process driving changes on industrial strains.

Ethanol production has key differences between the two largest producing countries of this biofuel, Brazil and the USA, such as feedstock source, sugar concentration and ethanol titers in industrial fermentation. Therefore, it is highly probable that these specificities have led to genome adaptation of the Saccharomyces cerevisiae strains employed in each process to tolerate different environments. In order to identify particular adaptations, in this work, we have compared the genomes of industrial yeast strains widely used to produce ethanol from sugarcane, corn and sweet sorghum, and also two laboratory strains as reference. The genes were predicted and then 4524 single-copy orthologous were selected to build the phylogenetic tree. We found that the geographic location and industrial process were shown as the main evolutionary drivers: for sugarcane fermentation, positive selection was identified for metal homeostasis and stress response genes, whereas genes involved in membrane modeling have been connected with corn fermentation. In addition, the corn specialized strain Ethanol Red showed an increased number of copies of MAL31, a gene encoding a maltose transporter. In summary, our work can help to guide new strain chassis selection for engineering strategies, to produce more robust strains for biofuel production and other industrial applications.

Comparison of Spathaspora passalidarum and recombinant Saccharomyces cerevisiae for integration of first- and second-generation ethanol production.

First-generation ethanol (E1G) is based on the fermentation of sugars released from saccharine or starch sources, while second-generation ethanol (E2G) is focused on the fermentation of sugars released from lignocellulosic feedstocks. During the fractionation process to release sugars from hemicelluloses (mainly xylose), some inhibitor compounds are released hindering fermentation. Thus, the biggest challenge of using hemicellulosic hydrolysate is selecting strains and processes able to efficiently ferment xylose and tolerate inhibitors. With the aim of diluting inhibitors, sugarcane molasses (80% of sucrose content) can be mixed to hemicellulosic hydrolysate in an integrated E1G-E2G process. Cofermentations of xylose and sucrose were evaluated for the native xylose consumer Spathaspora passalidarum and a recombinant Saccharomyces cerevisiae strain. The industrial S. cerevisiae strain CAT-1 was modified to overexpress the XYL1, XYL2 and XKS1 genes and a mutant ([4-59Δ]HXT1) version of the low-affinity HXT1 permease, generating strain MP-C5H1. Although S. passalidarum showed better results for xylose fermentation, this yeast showed intracellular sucrose hydrolysis and low sucrose consumption in microaerobic conditions. Recombinant S. cerevisiae showed the best performance for cofermentation, and a batch strategy at high cell density in bioreactor achieved unprecedented results of ethanol yield, titer and volumetric productivity in E1G-E2G production process.

Exploring metal ion metabolisms to improve xylose fermentation in Saccharomyces cerevisiae.

The development of high-performance xylose-fermenting yeast is essential to achieve feasible conversion of biomass-derived sugars in lignocellulose-based biorefineries. However, engineered C5-strains of Saccharomyces cerevisiae still present low xylose consumption rates under anaerobic conditions. Here, we explore alternative metabolisms involved in metal homeostasis, which positively affect C5 fermentation and analyse the non-obvious regulatory network connection of both metabolisms using time-course transcriptome analysis. Our results indicated the vacuolar Fe2+ /Mn2+ transporter CCC1, and the protein involved in heavy metal ion homeostasis BSD2, as promising new targets for rational metabolic engineering strategies, enhancing xylose consumption in nine and 2.3-fold compared with control. Notably, intracellular metal concentration levels were affected differently by mutations and the results were compared with positive controls isu1Δ, a Fe-S cluster scaffold protein, and ssk2Δ, a component of HOG pathway. Temporal expression profiles indicate a metabolic remodelling in response to xylose, demonstrating changes in the main sugar sensing signalling pathways.

Draft Genome Sequence of Saccharomyces cerevisiae Barra Grande (BG-1), a Brazilian Industrial Bioethanol-Producing Strain.

Here, we present the draft genome sequence of Saccharomyces cerevisiae BG-1, a Brazilian industrial strain widely used for bioethanol production from sugarcane. The 11.7-Mb genome sequence consists of 216 scaffolds and harbors 5,607 predicted protein-coding genes.