Soluble and stable cyanophycin synthetase expression enhances heterologous cyanophycin production in Escherichia coli

Microbial production of biopolymers represents a promising, sustainable alternative to current approaches for plastic production. Cyanophycin synthetase 1 (CphA1) produces cyanophycin - an attractive biopolymer consisting of a poly-L-aspartic acid backbone decorated with L-arginine side groups. In this work, a series of CphA1 enzymes from different bacteria that were each previously identified to express as soluble and stable enzymes in Escherichia coli were screened for heterologous cyanophycin production in engineered E. coli. In each case, expression of stable CphA1 enzymes resulted in greater insoluble cyanophycin production, and it was found that CphA1 from Tatumella morbirosei (TmCphA1) was especially productive. Under these conditions, TmCphA1 was capable of supporting up to ∼2-fold greater yields of insoluble cyanophycin than any other tested CphA1 enzymes, including 10.8-times more than CphA1 from Synechocystis sp. PCC6308. Finally, using a bench-scale bioreactor, cyanophycin production by TmCphA1-expressing E. coli reached up to 1.9 g per liter of culture by 48 h.