Project description:Clostridium ljungdahlii not only utilizes CO, but also H2 as energy source during autotrophic growth. And C. ljungdahlii also grows in fructose fermentation. In theory, fructose is a more energetically favourable energy source than syngas in the fermentation of C. ljungdahlii. However, C. ljungdahlii grows insufficiently in fructose and produces less acetate and ethanol, compared to syngas fermentation. In this study, C. ljungdahlii wild type and mutants were fermented on fructose. C. ljungdahlii produced less ethanol than the ΔadhE1 mutant and consumed less fructose. The ΔadhE1+2 mutant cannot grow in the syngas fermentation and produced less ethanol among the three strains. The results showed that aldehyde dehydrogenase inactivation led to efficient metabolism in C. ljungdahlii and the bifunctional aldehyde/alcohol dehydrogenases inactivation led to decrease metabolism. Thus, comparative transcriptomes among cells grown on fructose of three strains were performed to investigate gene expression profiles based on three biological replicates.
Project description:Microalgal biomass is a promising feedstock for biofuels, feed/food and biomaterials. However, while production and commercialization of single-product commodities is still not economically viable, obtaining multiple products in a biomass biorefinery faces several techno- economic challenges. The aim of this study was to identify a suitable source of hydrolytic enzymes for algal biomass saccharification. Screening of twenty-six fungal isolates for secreted enzymes activity on Chlamydomonas reinhardtii biomass resulted in the identification of Aspergillus niger IB-34 as a candidate strain. Solid state fermentation on wheat bran produced the most active enzyme preparations. From sixty-five proteins identified by LC-MS, the majority corresponded to predicted secreted proteins belonging to the Gene Ontology categories of catalytic activity/hydrolase activity on glycosyl and O-glycosyl compounds. Defatted biomass of the more biotechnologically relevant strains towards the production of commodities, Chlorella sorokiniana and Scenedesmus obliquus, was fully saccharified after a mild pretreatment at 80 °C for 10 min, at a high biomass load of 10 % (w/v). Deffated and 2 saccharified biomass of both strains was further converted into ethanol by fermentation with Saccharomyces cerevisiae at a theoretical maximum efficiency, either by separated or simultaneous sccharification and fermentation. The resulting insoluble protein after biomass defatting with an organic solvent and enzymatic saccharification resulted in a high digestibility in an in vitro digestion assay. Proof-of-concept is presented for an enzyme-assisted biomass biorefinery which recovered 81% of the main biomass fractions in a likely active form for the conversion of lipids and carbohydrates into biofuels and proteins into feed/food.
Project description:The yeast Dekkera bruxellensis is as ethanol tolerant as Saccharomyces cerevisiae and may be found in bottled wine. It causes the spoilage of wine, beer, cider and soft drinks. In wines, the metabolic products responsible for spoilage by Dekkera bruxellensis are mainly volatile phenols. These chemical compounds are responsible for the taints described as M-bM-^@M-^XM-bM-^@M-^XmedicinalM-bM-^@M-^YM-bM-^@M-^Y in white wines (due to vinyl phenols) and as M-bM-^@M-^XM-bM-^@M-^XleatherM-bM-^@M-^YM-bM-^@M-^Y, M-bM-^@M-^XM-bM-^@M-^Xhorse sweatM-bM-^@M-^YM-bM-^@M-^Y and M-bM-^@M-^XM-bM-^@M-^XstableM-bM-^@M-^YM-bM-^@M-^Y in red wines (due to ethyl phenols mainly 4-ethylphenol). Apart from the negative aroma nuances imparted by these yeasts, positive aromas such as M-bM-^@M-^XsmokyM-bM-^@M-^Y, M-bM-^@M-^XspicyM-bM-^@M-^Y and M-bM-^@M-^XtoffeeM-bM-^@M-^Y are also cited. Our goal was to identify the impact that the wine spoilage yeast Dekkera bruxellensis has on fermenting S. cerevisiae cells, especially on its gene expression level. To this end we co-inoculated both yeast species at the start of fermentation in a synthetic wine must, using S. cerevisiae-only fermentations without Dekkera bruxellensis as a control. All fermentations were employed in special membrane reactors (50 KDa pore size cut-off) physically separating Dekkera bruxellensis from wine yeast S. cerevisiae. Biomass separation with this membrane was done to abolish the possibility of hybridizing also D. bruxellensis probes on Agilent V2 (8x15K format) G4813 DNA microarrays designed just for S. cerevisiae ORF targets. The 50 KDa pore membrane separating both yeasts allowed the exchange of ethanol, metabolites and sugars during the fermentation. Fermentations were carried out in synthetic wine must in duplicate for both the control S. cerevisiae (strain Lalvin EC1118) and mixed fermentation. Sampling of yeast S. cerevisiae for RNA extractions were performed at 22 h of fermentation, during the exponential growth phase of S. cerevisiae, at 92 h and 144 h of fermentation, during its early and late stationary growth phase and at 187 h of fermentation, during its phase of growth decline.