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Substrate preference and oxygen requirement for cyanophycin synthesis by recombinant Escherichia coli

Solaiman, Daniel K.Y., Ashby, Richard D., Zerkowski, Jonathan A.
Biocatalysis and agricultural biotechnology 2012 v.1 no.1 pp. 9
Escherichia coli, Synechocystis, aeration, air flow, arginine, aspartic acid, biomass, fermentation, genes, glucose, glycerol, mixers, nutrient requirements, oxygen requirement, polypeptides
Cyanophycin (CGP) is a bacterial bioproduct having a straight-chain poly(aspartic acid) as a backbone with arginine pendant groups attached to it. It has many potential industrial applications in the areas of water softening, hydrogel, metal–ion chelation, and nutriceuticals. Biotechnological production of CGP employs as producing strains the recombinant organisms that express heterologous cyanophycin synthase (cph) gene. A systematic study of fermentation parameters influencing CGP synthesis by a recombinant Escherichia coli expressing a cphA of Synechocystis sp. showed that high aeration conditions as provided by 400 rpm stirrer speed and 1.0 L/min air flow in a Sixfors vessel (450 mL culture working-volume) resulted in high yields of cell biomass and crude CGP product. Glycerol substrate was found to yield 1.8-times higher crude CGP than glucose did under similar conditions. With glycerol as substrate, we found that a simplified fermentation scheme consisting of a straight 48-h fermentation at 37 °C (without a 30–37 °C temperature-shifting induction step) yielded compatible or higher amounts of crude CGP as those obtained under various temperature-shifting conditions. By studying the effects of glycerol concentration on CGP yields and analyzing glycerol consumption patterns, we demonstrated that substrate-to-product conversion could be increased by at least 15% and that costly leftover of unused substrate could be alleviated. The results yielded valuable information for optimization of fermentative production of CGP using glycerol that could be obtained as surplus coproduct from biodiesel production.