The deconstruction of lignin to enhance the release of fermentable sugars from plant cell walls presents a challenge for biofuels production from lignocellulosic biomass. The discovery of novel lignin-degrading enzymes from bacteria could provide advantages over fungal enzymes in terms of their production and relative ease of protein engineering. In this study, 140 bacterial strains isolated from soils of a biodiversity-rich rainforest in Peru were screened based on their oxidative activity on ABTS, a laccase substrate. Strain C6 (Bacillus pumilus) and strain B7 (Bacillus atrophaeus) were selected for their high laccase activity and identified by 16S rDNA analysis. Strains B7 and C6 degraded fragments of Kraft lignin and the lignin model dimer guaiacylglycerol-β-guaiacyl ether, the most abundant linkage in lignin. Finally, LC-MS analysis of incubations of strains B7 and C6 with poplar biomass in rich and minimal media revealed that a higher number of compounds were released in the minimal medium than in the rich one. These findings provide important evidence that bacterial enzymes can degrade and/or modify lignin and contribute to the release of fermentable sugars from lignocellulose.

No abstract

Cellulases, enzymes capable of depolymerizing cellulose polymers into fermentable sugars, are essential components in the production of bioethanol from lignocellulosic materials. Given the importance of these enzymes to the evolving biofuel industry considerable research effort is focused on understanding the interaction between cellulases and cellulose fibrils. This manuscript presents a method that addresses challenges that must be overcome in order to study such interactions through high-resolution fluorescence microscopy. First, it is shown that cellulose can be immobilized on solid substrates through a polymer lift-off technique. The immobilized cellulose aggregates present characteristic morphologies influenced by the patterned feature size used to immobilize it. Thus, through a variety of pattern sizes, cellulose can be immobilized in the form of cellulose particles, cellulose mats or individual cellulose fibrils. Second, it is shown that both cellulose and Thermobifida fusca cellulases Cel5A, Cel6B, and Cel9A can be fluorescently tagged and that the labeling does not inhibit the capability of these cellulases to depolymerize cellulose. The combination of the immobilization technique together with fluorescence labeling yields a system that can be used to study cellulose-cellulase interactions with spatial and temporal resolution not available through more conventional techniques which measure ensemble averages. It is shown that with such a system, the kinetics of cellulase binding onto cellulose fibrils and mats can be followed through sequences of fluorescence images. The intensity from the images can then be used to reconstruct binding curves for the cellulases studied. It was found that the complexity of cellulose morphology has a large impact on the binding curve characteristics, with binding curves for individual cellulose fibrils closely following a binding saturation model and binding curves for cellulose mats and particles deviating from it. The behavior observed is interpreted as the effect pore and interstice penetration play in cellulase binding to the accessible surface of cellulose aggregates. These results validate our method for immobilizing nanoscale cellulose fibrils and fibril aggregates on solid supports and lay the foundation for future studies on cellulase-cellulose interactions.

This work employs a coupled analysis of the fluid flow and heat transfer in the polymer melt during the filling and post-filling stages of the injection-molding process and of mold cooling/heating which occurs during the entire process. Polymer melt analysis (PMA) has been carried out through a unified theoretical model implemented using a hybrid finite-element/finite-difference/control-volume numerical solution of the generalized Hele-Shaw flow of a compressible viscous fluid under non-isothermal conditions. Further, mold-cooling analysis (MCA) has been carried out utilizing a periodic heat conduction model implemented using a modified three-dimensional boundary-element method. To faithfully accommodate the effects of mold cooling on the fluid flow and heat transfer in the polymer melt, PMA and MCA have been coupled for appropriate data exchange and iterations carried out until a convergent solution for mold temperatures and for flow, pressure and temperatures within the polymer melt is obtained. The results obtained from this integrated simulation for different test cases have been compared with experimental data and a favorable agreement has been noticed. Using an illustrative example, the results are discussed in detail.

ABSTRACT

Carbon storage in terrestrial ecosystems is contingent upon the natural resistance of plant cell wall polymers to rapid biological degradation. Nevertheless, certain microorganisms have evolved remarkable means to overcome this natural resistance. Lignocellulose decomposition by microorganisms comprises an essential step in closing the loop of the global carbon cycle as it facilitates the recycling of carbon reposited in the form of structural polymers in plant cell walls. The significance of microbial decomposition of lignocellulose has recently risen to greater heights with the revisitation of the potential of lignocellulosic biomass as a valuable and abundant feedstock for the renewable energy and bioproducts industry. The scope of this chapter is to succinctly touch upon the composition of lignocellulosic biomass, the major enzymes involved in decomposing lignocellulosic biomass, and the fungi and bacteria that secrete these enzymes.

No abstract

No abstract