Research progress on the biosynthesis and bioproduction of the biodegradable chelating agent (S,S)-EDDS

Ethylenediamine-N,N'-disuccinic acid [(S,S)-EDDS] is a biodegradable strong chelating agent that can currently be produced by biological methods, including fermentation and enzymatic synthesis. The fermentation of (S,S)-EDDS is mainly performed in Amycolatopsis japonicum MG417-CF17, and the highest fermentation level reported is 20 g/L. (S,S)-EDDS biosynthesis is inhibited by low-micromolar zinc concentrations. The gene cluster aesA-H is involved in the synthesis of (S,S)-EDDS, and (S)-N-(2-aminoethyl) aspartic acid (AEAA) is most likely to be a key intermediate coupling the biosynthesis and biodegradation of (S,S)-EDDS in microorganisms. The highest reported level of enzymatic synthesis of (S,S)-EDDS is 209 g/L. Most of the existing enzymatic synthetic routes use ethylenediamine and fumaric acid as substrates. When using aspartate ammonia lyase as a catalyst, the product is (R,S)-configured, while (S,S)-EDDS can be obtained with EDDS lyase. After purification and then immobilization, EDDS lyase was used in 11 batch reactions (864.5 h); the yield reached 94%, and the maximum space-time yield was 1.55 g/(L.h). Enzymatic methods have a clearer mechanism than fermentation and are more economical and environmentally friendly. By further optimizing the reaction conditions, this method is expected to replace chemical synthesis in manufacturing (S,S)-EDDS.