Biosynthesis of cyanophycin by high-cell-density cultivation of recombinant Escherichia coli for corrosion-resistant biomaterial applications.

Cyanophycin granule polypeptide (CGP), also known as multi-L-arginyl-poly(aspartic acid), is a biodegradable biopolymer composed primarily of aspartic acid and arginine. Due to its versatile functional properties, CGP has attracted increasing interest for potential applications in food, medicine, cosmetics, agriculture, and corrosion inhibition. The objective of this study was to biosynthesize a biologically derived corrosion-inhibiting biomaterial using recombinant Escherichia coli BL21(DE3) expressing cyanophycin synthetase (CphA), followed by cost-effective induction strategy. Specifically, this work aimed to establish a high-cell-density cultivation process capable of achieving improved CGP production while reducing dependence on costly inducers such as IPTG. Initial shake-flask experiments demonstrated that lactose induction resulted in higher CGP production and biomass formation compared to IPTG induction. In addition, supplementation with phosphate, ribose, trace elements, yeast extract, and tryptone further improved CGP accumulation. Based on these findings, a high-cell-density fed-batch fermentation strategy using lactose as both inducer and carbon source was developed, maximum gravimetrically recovered crude soluble and insoluble CGP-containing fractions of 35.4 and 17.8 g/L. Product characterization was further supported by FTIR, XRD, MALDI-MS. Furthermore, the recovered CGP-related material was evaluated in preliminary corrosion inhibition experiments under acidic conditions and showed significant reduction in corrosion rates compared with untreated control samples, indicating its potential for future corrosion-protection applications.