Browsing by Author "Van Zyl, W. H."

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    Converting plant biomass to fuels and commodity chemicals in South Africa : a third chapter?
    (Academy of Science for South Africa, 2003) Lynd, L. R.; Von Blottnltz, H.; Tait, B.; De Boer, J.; Pretorius, I. S.; Rumbold, K.; Van Zyl, W. H.
    THERE HAVE BEEN TWO DISTINCT CHAPTERS in the history of converting cellulosic biomass to fuels and commodity chemicals in South Africa. The first chapter, from the late 1970s to the early 1990s, involved some of the most active research and development efforts of their kind anywhere in the world. Thereafter, during the second chapter, there has been very little activity in the field in South Africa while there has been an unprecedented awakening to the potential of biomass conversion elsewhere. This paper considers the rationale and possible benefits of a potential third chapter based on a revitalized effort on biomass conversion in South Africa. Such an enterprise would build on the country's large biomass production potential, strong technical capability in yeast biotechnology, a well-developed research and development infrastructure in biological processing, and expertise derived from the largest non-petroleum hydrocarbon processing industry in the world. Substantial societal benefits could be realized that address critically important national needs, including the utilization of sustainable resources, industrial development, and improved balance of payments. Moreover, establishing a modern biomass processing industry in South Africa appears to represent one of the largest potential sources of rural employment identified to date. We propose steps to realizing these benefits.
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    Fruit waste streams in South Africa and their potential role in developing a bio-economy
    (Academy of Science of South Africa, 2015) Khan, Nuraan; Le Roes-Hill, Marilize; Welz, Pamela J.; Grandin, Kerry A.; Kudanga, Tukayi; Van Dyk, J. Susan; Ohlhoff, Colin; Van Zyl, W. H.; Pletschke, Brett I.
    Current and previous studies on bio-based (fruit) wastes and wastewaters, with a particular emphasis on research in South Africa, were reviewed. Previous studies have focused predominantly on the beneficiation and application of fruit waste as a feedstock for renewable energy. A definite gap in knowledge and application of fruit waste streams with regard to enzyme production as a value-added product is identified. The characteristics and composition of each type of fruit waste are highlighted and their potential as feedstocks in the production of value-added products is identified. The conversion of agri-industrial wastewaters to bioenergy and value-added products is discussed, with special mention of the newly published South African Bio-Economy Strategy, and the potential production of biofuels and enzymes from waste streams using recombinant Aspergillus strains. Finally, to maximise utilisation of waste streams in South Africa and abroad, a conceptual model for an integrated system using different technologies is proposed.
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    Modeling the minimum enzymatic requirements for optimal cellulose conversion
    (IoP Publising, 2013-04) Den Haan, R.; Van Zyl, J. M.; Harms, T. M.; Van Zyl, W. H.
    Hydrolysis of cellulose is achieved by the synergistic action of endoglucanases, exoglucanases and -glucosidases. Most cellulolytic microorganisms produce a varied array of these enzymes and the relative roles of the components are not easily defined or quantified. In this study we have used partially purified cellulases produced heterologously in the yeast Saccharomyces cerevisiae to increase our understanding of the roles of some of these components. CBH1 (Cel7), CBH2 (Cel6) and EG2 (Cel5) were separately produced in recombinant yeast strains, allowing their isolation free of any contaminating cellulolytic activity. Binary and ternary mixtures of the enzymes at loadings ranging between 3 and 100 mg g-1 Avicel allowed us to illustrate the relative roles of the enzymes and their levels of synergy. A mathematical model was created to simulate the interactions of these enzymes on crystalline cellulose, under both isolated and synergistic conditions. Laboratory results from the various mixtures at a range of loadings of recombinant enzymes allowed refinement of the mathematical model. The model can further be used to predict the optimal synergistic mixes of the enzymes. This information can subsequently be applied to help to determine the minimum protein requirement for complete hydrolysis of cellulose. Such knowledge will be greatly informative for the design of better enzymatic cocktails or processing organisms for the conversion of cellulosic biomass to commodity products.
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    Scalable methanol‑free production of recombinant glucuronoyl esterase in Pichia pastoris
    (BMC (part of Springer Nature), 2019) Conacher, C. G.; Garcia‑Aparicio, M. P.; Coetzee, G.; Van Zyl, W. H.; Gorgens, J. F.
    Objective: Glucuronoyl esterase (GE) is an emerging enzyme that improves fractionation of lignin-carbohydrate complexes. However, the commercial availability of GE is limited, which hinders the research of GE-based bioprocesses for its industrial application in lignocellulose biorefineries. This study evaluated a workable, cost-effective, and commercially scalable production strategy to improve the ease of GE-based research. This strategy consisted of a constitutive and methanol-free enzyme production step coupled with a two-step filtration process. The aim was to determine if this strategy can yield copious amounts of GE, by secretion into the extracellular medium with an acceptable purity that could allow its direct application. This approach was further validated for cellobiose dehydrogenase, another emerging lignocellulose degrading enzyme which is scarcely available at high cost. Results: The secreted recombinant enzymes were functionally produced in excess of levels previously reported for constitutive production (1489–2780 mg L−1), and were secreted at moderate to high percentages of the total extracellular protein (51–94%). The constant glycerol feed, implemented during fed-batch fermentation, lead to a decline in growth rate and plateaued productivity. Tangential flow ultrafiltration was used to concentrate cell-free enzyme extracts 5–6-fold, reaching enzyme activity levels (1020–202 U L−1) that could allow their direct application.