Combined inactivation of the Clostridium cellulolyticum lactate and malate dehydrogenase genes substantially increases ethanol yield from cellulose and switchgrass fermentations

<p>Abstract</p> <p>Background</p> <p>The model bacterium <it>Clostridium cellulolyticum </it>efficiently degrades crystalline cellulose and hemicellulose, using cellulosomes to degrade lignocellulosic biomass. Although it imports and ferments both pentose and hexose sugars to produce a mixture of ethanol, acetate, lactate, H₂and CO₂, the proportion of ethanol is low, which impedes its use in consolidated bioprocessing for biofuels production. Therefore genetic engineering will likely be required to improve the ethanol yield. Plasmid transformation, random mutagenesis and heterologous expression systems have previously been developed for <it>C. cellulolyticum</it>, but targeted mutagenesis has not been reported for this organism, hindering genetic engineering.</p> <p>Results</p> <p>The first targeted gene inactivation system was developed for <it>C. cellulolyticum</it>, based on a mobile group II intron originating from the <it>Lactococcus lactis </it>L1.LtrB intron. This markerless mutagenesis system was used to disrupt both the paralogous <smcaps>L</smcaps>-lactate dehydrogenase (<it>Ccel_2485; ldh</it>) and <smcaps>L</smcaps>-malate dehydrogenase (<it>Ccel_0137; mdh</it>) genes, distinguishing the overlapping substrate specificities of these enzymes. Both mutations were then combined in a single strain, resulting in a substantial shift in fermentation toward ethanol production. This double mutant produced 8.5-times more ethanol than wild-type cells growing on crystalline cellulose. Ethanol constituted 93% of the major fermentation products, corresponding to a molar ratio of ethanol to organic acids of 15, versus 0.18 in wild-type cells. During growth on acid-pretreated switchgrass, the double mutant also produced four times as much ethanol as wild-type cells. Detailed metabolomic analyses identified increased flux through the oxidative branch of the mutant's tricarboxylic acid pathway.</p> <p>Conclusions</p> <p>The efficient intron-based gene inactivation system produced the first non-random, targeted mutations in <it>C. cellulolyticum</it>. As a key component of the genetic toolbox for this bacterium, markerless targeted mutagenesis enables functional genomic research in <it>C</it>. <it>cellulolyticum </it>and rapid genetic engineering to significantly alter the mixture of fermentation products. The initial application of this system successfully engineered a strain with high ethanol productivity from cellobiose, cellulose and switchgrass.</p

Recherche d’un milieu optimal pour la production de la - glucosidase chez Aspergillus fumigatus (FRESENIUS) albino

info:eu-repo/semantics/publishe

Performance Analysis of the Mini-grid Connected Photovoltaic System at Algiers

AbstractThis paper analyses the operating performance of the Grid connected Photovoltaic (PV) System installed on the terrace of the administrative building of the Centre de Développement des Energies Renouvelables (CDER) in Algiers. We present the results of the performance evaluation of the energy installation on a typical year. Energy losses and the most significant performance of the system are quantified. During this period, the system has produced an annual 10 981 kWh of energy injected into the grid. This means an average daily energy of 30 kWh, with performance ratio between 62 and 77%. In comparison with similar systems performance in other countries, the results indicate that the power generated by the CDER grid connected PV system meets the specifications required for such systems compared to international standards

Duplication appendiculaire révélé à l’occasion d’un syndrome appendiculaire récidivant

La duplication appendiculaire est une malformation très rare. Elle se rencontre chez les enfants exceptionnellement chez les adultes. Sa découverte est  souvent fortuite à l'occasion d'une laparotomie ou laparoscopie pour une  autre pathologie. Nous rapportons un cas particulier d'un patient qui a  bénéficié d'une appendicectomie il y'a 3 mois qui est admis aux urgences pour un syndrome appendiculaire récidivant avec aux explorations  radiologique et chirurgicale la présence d'une appendicite rétrocoecale

The Extracellular Xylan Degradative System in <i>Clostridium cellulolyticum</i> Cultivated on Xylan: Evidence for Cell-Free Cellulosome Production

ABSTRACT In this study, we demonstrate that the cellulosome of Clostridium cellulolyticum grown on xylan is not associated with the bacterial cell. Indeed, the large majority of the activity (about 90%) is localized in the cell-free fraction when the bacterium is grown on xylan. Furthermore, about 70% of the detected xylanase activity is associated with cell-free high-molecular-weight complexes containing avicelase activity and the cellulosomal scaffolding protein CipC. The same repartition is observed with carboxymethyl cellulase activity. The cellulose adhesion of xylan-grown cells is sharply reduced in comparison with cellulose-grown cells. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis revealed that cellulosomes derived from xylan- and cellulose-grown cells have different compositions. In both cases, the scaffolding protein CipC is present, but the relative proportions of the other components is dramatically changed depending on the growth substrate. We propose that, depending on the growth substrate, C. cellulolyticum is able to regulate the cell association and cellulose adhesion of cellulosomes and regulate cellulosomal composition. </jats:p