Structural reorganisation of cellulose fibrils in hydrothermally deconstructed lignocellulosic biomass and relationships with enzyme digestibility

Background: The investigation of structural organisation in lignocellulose materials is important to understand changes in cellulase accessibility and reactivity resulting from hydrothermal deconstruction, to allow development of strategies to maximise bioethanol process efficiencies. To achieve progress, wheat straw lignocellulose and comparative model wood cellulose were characterised following increasing severity of hydrothermal treatment. Powder and fibre wide-angle X-ray diffraction techniques were employed (WAXD), complemented by enzyme kinetic measurements up to high conversion. Results: Evidence from WAXD indicated that cellulose fibrils are not perfectly crystalline. A reduction in fibril crystallinity occurred due to hydrothermal treatment, although dimensional and orientational data showed that fibril coherency and alignment were largely retained. The hypothetical inter-fibril spacing created by hydrothermal deconstruction of straw was calculated to be insufficient for complete access by cellulases, although total digestion of cellulose in both treated straw and model pulp was observed. Both treated straw and model pulps were subjected to wet mechanical attrition, which caused separation of smaller fibril aggregates and fragments, significantly increasing enzyme hydrolysis rate. No evidence from WAXD measurements was found for preferential hydrolysis of non-crystalline cellulose at intermediate extent of digestion, for both wood pulp and hydrothermally treated straw. Conclusions: The increased efficiency of enzyme digestion of cellulose in the lignocellulosic cell wall following hydrothermal treatment is a consequence of the improved fibril accessibility due to the loss of hemicellulose and disruption of lignin. However, incomplete accessibility of cellulase at the internal surfaces of fibrillar aggregates implies that etching type mechanisms will be important in achieving complete hydrolysis. The reduction in crystalline perfection following hydrothermal treatment may lead to an increase in fibril reactivity, which could amplify the overall improvement in rate of digestion due to accessibility gains. The lack of preferential digestion of non-crystalline cellulose is consistent with the existence of localised conformational disorder, at surfaces and defects, according to proposed semicrystalline fibril models. Cellulases may not interact in a fully selective manner with such disordered environments, so fibril reactivity may be considered as a function of average conformational states

Concertacion y seguridad social : de la legitimidad social a la legitimidad tecnocrática

El estudio aborda la concertación, un análisis de las políticas de seguridad social constatando su evolución desde una legitimidad social a una legitimidad tecnocrática en la crisis del welfare state y en la crisis económica con particular referencia al sistema español. Desde la normalización de la acción política de los sindicatos y agentes sociales en sus diversas manifestaciones, como la participación institucional y la "legislación negociada" en la búsqueda del consenso y el negociado de intercambios en el marco político frente a la imposición unilateral. La frustración de la concertación social se produce cuando el gobierno interpreta la democracia como algo puramente aritmético de mayorías que ejercen sin más el poder, en épocas de debilidad sindical, de debilidad del estado nación, de dificultades para las políticas redistributivas, de reforzamiento de los planteamientos neoliberales. La búsqueda de legitimidad en el pacto social no se ve en estas ocasiones como necesaria sino que la legitimidad se traslada al discurso economicista y tecnocrático, no político. Se vuelve a la búsqueda de una legitimidad a través del mercado y del intercambio entre particulares.L'estudi aborda la concertació, una anàlisi de les polítiques de seguretat social constatant la seva evolució des d'una legitimitat social a una legitimitat tecnocràtica en la crisi del welfare state i en la crisi econòmica amb particular referència al sistema espanyol. Des de la normalització de l'acció política dels sindicats i agents socials en les seves diverses manifestacions, com la participació institucional i la "legislació negociada" en la cerca del consens i el negociat d'intercanvis en el marc polític enfront de la imposició unilateral. La frustració de la concertació social es produeix quan el govern interpreta la democràcia com alguna cosa purament aritmètic de majories que exerceixen sense més el poder, en èpoques de feblesa sindical, de feblesa de l'estat nació, de dificultats per a les polítiques redistributives, de reforçament dels plantejaments neoliberals. La cerca de legitimitat en el pacte social no es veu en aquestes ocasions com a necessària sinó que la legitimitat es trasllada al discurs economicista i tecnocràtic, no polític. Es torna a la cerca d'una legitimitat a través del mercat i de l'intercanvi entre particulars.The study addresses the conclusion an analysis of policies of social security noting exposing its evolution from a social legitimacy to a technocratic legitimacy in the crisis of the welfare state and the economic crisis with particular reference to the Spanish system. Since the normalization of the political action of the trade unions and social partners in its various manifestations, such as institutional participation and negotiated "legislation" in the search for consensus and the Bureau of exchanges in the political framework against the unilateral imposition. The frustration of the social agreement occurs when the Government interprets the democracy as something purely arithmetic of majorities that exercise without more power, in times of Union weakness, weakness of the State nation, of difficulties for redistributive policies, strengthening of neoliberal approaches. The search for legitimacy in the social pact is not on these occasions as necessary but that legitimacy is moved to the economistic and technocratic, non-political speech. Turns to the search for legitimacy through the market and the exchange between individuals

Understanding the mechanisms of cooperative physico-chemical treatment and mechanical disintegration of biomass as a route for enhancing enzyme saccharification

A novel chemico-kinetic disintegration model has been applied to study the cooperative relationship between physico-chemical treatment and supplementary wet-state milling of biomass, as an efficient process route to achieve high enzyme accessibility. Wheat straw, Miscanthus and short-rotation willow were studied as three contrasting biomass species, which were subjected to controlled hydrothermal pretreatment using a microwave reactor, followed by controlled wet-state ball-milling. Comparative particle disintegration behaviour and related enzyme digestibilities have been interpreted on the basis of model parameters and with evaluation of textural and chemical differences in tissue structures, aided by the application of specific material characterisation techniques. Supplementary milling led to a 1.3×, 1.6× and 3× enhancement in glucose saccharification yield after 24 h for straw, Miscanthus and willow, respectively, following a standardised 10-min hydrothermal treatment, with corresponding milling energy savings of 98, 97 and 91% predicted from the model, compared to the unmilled case. The results confirm the viability of pretreatment combined with supplementary wet-milling as an efficient process route. The results will be valuable in understanding the key parameters for process design and optimisation and also the key phenotypical parameters for feedstock breeding and selection for highest saccharification yield

Succession of physiological stages hallmarks the transcriptomic response of the fungus Aspergillus niger to lignocellulose.

BackgroundUnderstanding how fungi degrade lignocellulose is a cornerstone of improving renewables-based biotechnology, in particular for the production of hydrolytic enzymes. Considerable progress has been made in investigating fungal degradation during time-points where CAZyme expression peaks. However, a robust understanding of the fungal survival strategies over its life time on lignocellulose is thereby missed. Here we aimed to uncover the physiological responses of the biotechnological workhorse and enzyme producer Aspergillus niger over its life time to six substrates important for biofuel production.ResultsWe analysed the response of A. niger to the feedstock Miscanthus and compared it with our previous study on wheat straw, alone or in combination with hydrothermal or ionic liquid feedstock pretreatments. Conserved (substrate-independent) metabolic responses as well as those affected by pretreatment and feedstock were identified via multivariate analysis of genome-wide transcriptomics combined with targeted transcript and protein analyses and mapping to a metabolic model. Initial exposure to all substrates increased fatty acid beta-oxidation and lipid metabolism transcripts. In a strain carrying a deletion of the ortholog of the Aspergillus nidulans fatty acid beta-oxidation transcriptional regulator farA, there was a reduction in expression of selected lignocellulose degradative CAZyme-encoding genes suggesting that beta-oxidation contributes to adaptation to lignocellulose. Mannan degradation expression was wheat straw feedstock-dependent and pectin degradation was higher on the untreated substrates. In the later life stages, known and novel secondary metabolite gene clusters were activated, which are of high interest due to their potential to synthesize bioactive compounds.ConclusionIn this study, which includes the first transcriptional response of Aspergilli to Miscanthus, we highlighted that life time as well as substrate composition and structure (via variations in pretreatment and feedstock) influence the fungal responses to lignocellulose. We also demonstrated that the fungal response contains physiological stages that are conserved across substrates and are typically found outside of the conditions with high CAZyme expression, as exemplified by the stages that are dominated by lipid and secondary metabolism

A proposed biomass char classification system

A new classification system is proposed for the morphological characterisation of char structures from biomass. These char structures are unlike the coal chars that have an established nomenclature via the International Committee of Coal and Organic Petrology (ICCP) which divides char structures into thin walled and thick walled spheres and networks, mixed dense and mixed porous, fusinoids and solids. The chars from biomass show a tendency, depending on heating regime, to produce different types of internal pore structure (cellular and porous) and aspect ratio (high and low) compared with coal chars. For this reason a new classification system has been developed to cover these new structures which should assist in combustion, co-firing and gasification research where these intermediate char structures play an important role in conversion efficiency. Low heating rates (using a muffle furnace at 1000°C and 3min) were used to create chars from 9 different biomass types, with a range of lignocellulosic compositions. Char type appeared to depend on the biomass type itself and original lignocellulosic composition (cellulose, lignin and hemicellulose content) and cell structure

Lunar daily variations of horizontal drifts in the E- and F2-regions

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Uncovering the genome-wide transcriptional responses of the filamentous fungus Aspergillus niger to lignocellulose using RNA sequencing

A key challenge in the production of second generation biofuels is the conversion of lignocellulosic substrates into fermentable sugars. Enzymes, particularly those from fungi, are a central part of this process, and many have been isolated and characterised. However, relatively little is known of how fungi respond to lignocellulose and produce the enzymes necessary for dis-assembly of plant biomass. We studied the physiological response of the fungus Aspergillus niger when exposed to wheat straw as a model lignocellulosic substrate. Using RNA sequencing we showed that, 24 hours after exposure to straw, gene expression of known and presumptive plant cell wall–degrading enzymes represents a huge investment for the cells (about 20% of the total mRNA). Our results also uncovered new esterases and surface interacting proteins that might form part of the fungal arsenal of enzymes for the degradation of plant biomass. Using transcription factor deletion mutants (xlnR and creA) to study the response to both lignocellulosic substrates and low carbon source concentrations, we showed that a subset of genes coding for degradative enzymes is induced by starvation. Our data support a model whereby this subset of enzymes plays a scouting role under starvation conditions, testing for available complex polysaccharides and liberating inducing sugars, that triggers the subsequent induction of the majority of hydrolases. We also showed that antisense transcripts are abundant and that their expression can be regulated by growth conditions