Recombinant E. coli Cellulases, β-Glucosidase, and Polygalacturonase Convert a Citrus Processing Waste into Biofuel Precursors

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ACS Sustainable Chemistry and Engineering


Molecular and biochemical characterization of lignocellulohydrolases cel12B, cel8C, β-glucosidase, and peh28 from Pectobacterium carotovorum subsp. carotovorum (Pcc) expressed in Escherichia coli (E. coli) was reported in a previous work. The current preliminary study investigates the enzymes' catalytic performance on Rio-Red grapefruit processing waste (GPW) conversion which can lead to the development of low-cost and effective strategies with strain engineering and/or modified catalysts for production of biofuel precursors. The GPW utilized for the study is known for its low ash and lignin contents compared with corn stover, wheat straw, and sugar cane bagasse, while yielding soluble sugars and polysaccharide constituents proportionally comparable to wastes from other citrus sources. Pretreatment of GPW at 120 °C with 1% w/w NaOH for 15 min resulted in significant total solid losses due primarily to conversion of glucans and lignin. Subsequent enzymatic bioconversion using the recombinant E. coli lignocellulolytic system resulted in production of 24, 11, and 14 g/kg solid biomass for the respective glucose, cellobiose, and galacturonic acid products from GPW over 24 h at 45 °C and pH 5.4. Other sugar products (e.g., xylose, arabinose, galactose, mannose, and rhamnose) were also detectable throughout the catalysis but at lower concentrations compared with the main products.

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