Browsing by Author "Lynd, Lee R."

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    Bioenergy and African transformation
    (BioMed Central, 2015-02) Lynd, Lee R.; Sow, Mariam; Chimphango, Annie F. A.; Cortez, Luis A. B.; Brito Cruz, Carlos H.; Elmissiry, Mosad; Laser, Mark; Mayaki, Ibrahim A.; Moraes, Marcia A. F. D.; Nogueira, Luiz A. H.; Wolfaardt, Gideon M.; Woods, Jeremy; Van Zyl, Willem H.
    Among the world’s continents, Africa has the highest incidence of food insecurity and poverty and the highest rates of population growth. Yet Africa also has the most arable land, the lowest crop yields, and by far the most plentiful land resources relative to energy demand. It is thus of interest to examine the potential of expanded modern bioenergy production in Africa. Here we consider bioenergy as an enabler for development, and provide an overview of modern bioenergy technologies with a comment on application in an Africa context. Experience with bioenergy in Africa offers evidence of social benefits and also some important lessons. In Brazil, social development, agricultural development and food security, and bioenergy development have been synergistic rather than antagonistic. Realizing similar success in African countries will require clear vision, good governance, and adaptation of technologies, knowledge, and business models to myriad local circumstances. Strategies for integrated production of food crops, livestock, and bioenergy are potentially attractive and offer an alternative to an agricultural model featuring specialized land use. If done thoughtfully, there is considerable evidence that food security and economic development in Africa can be addressed more effectively with modern bioenergy than without it. Modern bioenergy can be an agent of African transformation, with potential social benefits accruing to multiple sectors and extending well beyond energy supply per se. Potential negative impacts also cut across sectors. Thus, institutionally inclusive multi-sector legislative structures will be more effective at maximizing the social benefits of bioenergy compared to institutionally exclusive, single-sector structures.
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    Functional expression of cellobiohydrolases in Saccharomyces cerevisiae towards one-step conversion of cellulose to ethanol
    (Elsevier, 2006-09) Den Haan, Riaan; Mcbride, John E.; La Grange, Daniel C.; Lynd, Lee R.; Van Zyl, Willem H.
    To investigate the possible use of Saccharomyces cerevisiae as a candidate for consolidated bioprocessing (CBP) of cellulose to ethanol, four fungal cellobiohydrolase (CBH) encoding genes (Trichoderma reesei cbh1 and cbh2, Aspergillus niger cbhB and Phanerochaete chrysosporium cbh1–4) were expressed in this yeast. All four CBHs were successfully expressed and similar extracellular activity was demonstrated on phosphoric acid swollen cellulose (PASC) and bacterial microcrystalline cellulose (BMCC) using a modified affinity digestion procedure. Our results suggest that although heterologous CBHs can be produced in S. cerevisiae the titers of functionally secreted CBH are relatively low. However, the specific activity of recombinant CBH1 on PASC and BMCC, determined by a sensitive ELISA-based technique, was found not to differ significantly from that of the native T. reesei enzyme. Given this similarity in specific activity, but the disparity between current levels of CBH expression relative to expression levels required to enable growth on crystalline cellulosic substrates with concomitant ethanol production, future studies should aim to increase the expression levels of CBHs.
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    Tracking the cellulolytic activity of Clostridium thermocellum biofilms
    (BioMed Central, 2013-11-29) Dumitrache, Alexandru; Wolfaardt, Gideon M.; Allen, David Grand; Liss, Steven N.; Lynd, Lee R.
    Background Microbial cellulose conversion by Clostridium thermocellum 27405 occurs predominantly through the activity of substrate-adherent bacteria organized in thin, primarily single cell-layered biofilms. The importance of cellulosic surface exposure to microbial hydrolysis has received little attention despite its implied impact on conversion kinetics. Results We showed the spatial heterogeneity of fiber distribution in pure cellulosic sheets, which made direct measurements of biofilm colonization and surface penetration impossible. Therefore, we utilized on-line measurements of carbon dioxide (CO2) production in continuous-flow reactors, in conjunction with confocal imaging, to observe patterns of biofilm invasion and to indirectly estimate microbial accessibility to the substrate’s surface and the resulting limitations on conversion kinetics. A strong positive correlation was found between cellulose consumption and CO2 production (R2 = 0.996) and between surface area and maximum biofilm activity (R2 = 0.981). We observed an initial biofilm development rate (0.46 h-1, 0.34 h-1 and 0.33 h-1) on Whatman sheets (#1, #598 and #3, respectively) that stabilized when the accessible surface was maximally colonized. The results suggest that cellulose conversion kinetics is initially subject to a microbial limitation period where the substrate is in excess, followed by a substrate limitation period where cellular mass, in the form of biofilms, is not limiting. Accessible surface area acts as an important determinant of the respective lengths of these two distinct periods. At end-point fermentation, all sheets were digested predominantly under substrate accessibility limitations (e.g., up to 81% of total CO2 production for Whatman #1). Integration of CO2 production rates over time showed Whatman #3 underwent the fastest conversion efficiency under microbial limitation, suggestive of best biofilm penetration, while Whatman #1 exhibited the least recalcitrance and the faster degradation during the substrate limitation period. Conclusion The results showed that the specific biofilm development rate of cellulolytic bacteria such as C. thermocellum has a notable effect on overall reactor kinetics during the period of microbial limitation, when ca. 20% of cellulose conversion occurs. The study further demonstrated the utility of on-line CO2 measurements as a method to assess biofilm development and substrate digestibility pertaining to microbial solubilization of cellulose, which is relevant when considering feedstock pre-treatment options.
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    Tracking the cellulolytic activity of Clostridium thermocellum biofilms
    (BioMed Central, 2013-11-29) Dumitrache, Alexandru; Wolfaardt, Gideon M.; Allen, David Grant; Liss, Steven N.; Lynd, Lee R.
    Background: Microbial cellulose conversion by Clostridium thermocellum 27405 occurs predominantly through the activity of substrate-adherent bacteria organized in thin, primarily single cell-layered biofilms. The importance of cellulosic surface exposure to microbial hydrolysis has received little attention despite its implied impact on conversion kinetics. Results: We showed the spatial heterogeneity of fiber distribution in pure cellulosic sheets, which made direct measurements of biofilm colonization and surface penetration impossible. Therefore, we utilized on-line measurements of carbon dioxide (CO2) production in continuous-flow reactors, in conjunction with confocal imaging, to observe patterns of biofilm invasion and to indirectly estimate microbial accessibility to the substrate’s surface and the resulting limitations on conversion kinetics. A strong positive correlation was found between cellulose consumption and CO2 production (R2 = 0.996) and between surface area and maximum biofilm activity (R2 = 0.981). We observed an initial biofilm development rate (0.46 h-1, 0.34 h-1 and 0.33 h-1) on Whatman sheets (#1, #598 and #3, respectively) that stabilized when the accessible surface was maximally colonized. The results suggest that cellulose conversion kinetics is initially subject to a microbial limitation period where the substrate is in excess, followed by a substrate limitation period where cellular mass, in the form of biofilms, is not limiting. Accessible surface area acts as an important determinant of the respective lengths of these two distinct periods. At end-point fermentation, all sheets were digested predominantly under substrate accessibility limitations (e.g., up to 81% of total CO2 production for Whatman #1). Integration of CO2 production rates over time showed Whatman #3 underwent the fastest conversion efficiency under microbial limitation, suggestive of best biofilm penetration, while Whatman #1 exhibited the least recalcitrance and the faster degradation during the substrate limitation period. Conclusion: The results showed that the specific biofilm development rate of cellulolytic bacteria such as C. thermocellum has a notable effect on overall reactor kinetics during the period of microbial limitation, when ca. 20% of cellulose conversion occurs. The study further demonstrated the utility of on-line CO2 measurements as a method to assess biofilm development and substrate digestibility pertaining to microbial solubilization of cellulose, which is relevant when considering feedstock pre-treatment options.