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Research Publications (Applied Sciences)

Permanent URI for this collectionhttp://ir-dev.dut.ac.za/handle/10321/213

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    Display of phytase on the cell surface of Saccharomyces cerevisiae to degrade phytate phosphorus and improve bioethanol production
    (Springer Verlag, 2016) Xiao, Yan; Shen, Wei; Govender, Algasan; Zhang, Liang; Xianzhong, Chen
    Currently, development of biofuels as an alternative fuel has gained much attention due to resource and environ-mental challenges. Bioethanol is one of most important and dominant biofuels, and production using corn or cassava as raw materials has become a prominent technology. However, phytate contained in the raw material not only decreases the efficiency of ethanol production, but also leads to an increase in the discharge of phosphorus, thus impacting on the environment. In this study, to decrease phytate and its phos-phorus content in an ethanol fermentation process, Saccharomyces cerevisiae was engineered through a surface-displaying system utilizing the C-terminal half of the yeast α-agglutinin protein. The recombinant yeast strain, PHY, was constructed by successfully displaying phytase on the surface of cells, and enzyme activity reached 6.4 U/g wet biomass weight. Ethanol productions using various strains were com-pared, and the results demonstrated that the specific growth rate and average fermentation rate of the PHY strain were higher 20 and 18 %, respectively, compared to the control strain S. cerevisiae CICIMY0086, in a 5-L bioreactor process by simultaneous saccharification and fermentation. More im-portantly, the phytate phosphorus concentration decreased by 89.8 % and free phosphorus concentration increased by 142.9 % in dry vinasse compared to the control in a 5-L bio-reactor. In summary, we constructed a recombinant S. cerevisiae strain displaying phytase on the cell surface, which could improve ethanol production performance and effectively reduce the discharge of phosphorus. The strain reported here represents a useful novel engineering platform for developing an environment-friendly system for bioethanol production from a corn substrate.
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    Improvement of d-lactate productivity in recombinant Escherichia coli by coupling production with growth
    (Springer Netherlands, 2012-06) Zhou, Li; Tian, Kang-Ming; Niu, Dan-Dan; Shen, Wei; Shi, Fui-Yang; Singh, Suren; Wang, Zheng-Xiang
    Coupling lactate fermentation with cell growth was investigated in shake-flask and bioreactor cultivation systems by increasing aeration to improve lactate productivity in Escherichia coli CICIM B0013-070 (ackA pta pps pflB dld poxB adhE frdA). In shake-flasks, cells reached 1 g dry wt/l then, cultivated at 100 rpm and 42°C, achieved a twofold higher productivity of lactic acid compared to aerobic and O2-limited two-phase fermentation. The cells in the bioreactor yielded an overall volumetric productivity of 5.5 g/l h and a yield of 86 g lactic acid/100 g glucose which were 66% higher and the same level compared to that of the aerobic and O2-limited two-phase fermentation, respectively, using scaled-up conditions optimized from shake-flask experiments. These results have revealed an approach for improving production of fermentative products in E. coli.