Development of a D-xylose fermenting and inhibitor tolerant industrial Saccharomyces cerevisiae strain with high performance in lignocellulose hydrolysates using metabolic and evolutionary engineering

Background: The production of bioethanol from lignocellulose hydrolysates requires a robust, D-xylose-fermenting and inhibitor-tolerant microorganism as catalyst. The purpose of the present work was to develop such a strain from a prime industrial yeast strain, Ethanol Red, used for bioethanol production. Results: An expression cassette containing 13 genes including Clostridium phytofermentans XylA, encoding D-xylose isomerase (XI), and enzymes of the pentose phosphate pathway was inserted in two copies in the genome of Ethanol Red. Subsequent EMS mutagenesis, genome shuffling and selection in D-xylose-enriched lignocellulose hydrolysate, followed by multiple rounds of evolutionary engineering in complex medium with D-xylose, gradually established efficient D-xylose fermentation. The best-performing strain, GS1.11-26, showed a maximum specific D-xylose consumption rate of 1.1 g/g DW/h in synthetic medium, with complete attenuation of 35 g/L D-xylose in about 17 h. In separate hydrolysis and fermentation of lignocellulose hydrolysates of Arundo donax (giant reed), spruce and a wheat straw/hay mixture, the maximum specific D-xylose consumption rate was 0.36, 0.23 and 1.1 g/g DW inoculum/h, and the final ethanol titer was 4.2, 3.9 and 5.8% (v/v), respectively. In simultaneous saccharification and fermentation of Arundo hydrolysate, GS1.11-26 produced 32% more ethanol than the parent strain Ethanol Red, due to efficient D-xylose utilization. The high D-xylose fermentation capacity was stable after extended growth in glucose. Cell extracts of strain GS1.11-26 displayed 17-fold higher XI activity compared to the parent strain, but overexpression of XI alone was not enough to establish D-xylose fermentation. The high D-xylose consumption rate was due to synergistic interaction between the high XI activity and one or more mutations in the genome. The GS1.11-26 had a partial respiratory defect causing a reduced aerobic growth rate. Conclusions: An industrial yeast strain for bioethanol production with lignocellulose hydrolysates has been developed in the genetic background of a strain widely used for commercial bioethanol production. The strain uses glucose and D-xylose with high consumption rates and partial cofermentation in various lignocellulose hydrolysates with very high ethanol yield. The GS1.11-26 strain shows highly promising potential for further development of an all-round robust yeast strain for efficient fermentation of various lignocellulose hydrolysates

‘Generatieverschillen’ op het werk. Overzicht van een halve eeuw onderzoek

Generatie Y zorgt al jaren voor veel vooroordelen en speculaties in de praktijkliteratuur. Het vele onderzoek dat generaties op het werk analyseert, heeft tot nu geen eenduidige resultaten opgeleverd en is bovendien onderhevig aan verscheidene theoretische en methodologische problemen. Aan de hand van een uitgebreid literatuuroverzicht analyseren we in dit artikel de studies die over generaties op het werk verschenen. We maken hierbij telkens een verschil tussen bevindingen die echt over generaties gaan (gebaseerd op tijdsintervalstudies) en studies die iets zeggen over jongeren op het werk (cross-sectioneel onderzoek). Onze resultaten groeperen we rond zes thema’s: werkinhoud en - context, werk en de balans met het privéleven, werkgerelateerde attitude en gedrag, intrinsieke en extrinsieke bronnen voor motivatie op het werk, sociale contacten op het werk, en werkuitkomsten. We concluderen dat resultaten uit cross-sectionele en tijdsintervalstudies elkaar frequent tegenspreken. Leeftijdsgroepen blijken op nagenoeg alle zes thema’s onderling te verschillen. De generatieverschillen die we terugvinden, zijn in het algemeen beperkt en gering. Wij moedigen beleidsmakers daarom aan een beleid te hanteren dat ruimte geeft aan persoonlijke omstandigheden, behoeften en voorkeuren, meer dan beleid te voeren op groepen. Een algemener beleid kan worden opgezet rond loopbaanontwikkeling, opleiding en algemene ontwikkeling, factoren die leden van alle leeftijdsgroepen motiveren en nu beduidend belangrijker gevonden worden dan twintig jaar geleden.status: publishe

Novel dynamics of human mucociliary differentiation revealed by single-cell RNA sequencing of nasal epithelial cultures

The upper airway epithelium, which is mainly composed of multiciliated, goblet, club and basal cells, ensures proper mucociliary function and can regenerate in response to assaults. In chronic airway diseases, defective repair leads to tissue remodeling. Delineating key drivers of differentiation dynamics can help understand how normal or pathological regeneration occurs. Using single-cell transcriptomics and lineage inference, we have unraveled trajectories from basal to luminal cells, providing novel markers for specific populations. We report that: (1) a precursor subgroup of multiciliated cells, which we have entitled deuterosomal cells, is defined by specific markers, such as DEUP1, FOXN4, YPEL1, HES6 and CDC20B; (2) goblet cells can be precursors of multiciliated cells, thus explaining the presence of hybrid cells that co-express markers of goblet and multiciliated cells; and (3) a repertoire of molecules involved in the regeneration process, such as keratins or components of the Notch, Wnt or BMP/TGFβ pathways, can be identified. Confirmation of our results on fresh human and pig airway samples, and on mouse tracheal cells, extend and confirm our conclusions regarding the molecular and cellular choreography at work during mucociliary epithelial differentiation