D-Lysine production from L-lysine by successive chemical racemization and microbial asymmetric degradation

In order to develop a practical process for D-lysine production from L-lysine, successive chemical racemization and microbial asymmetric degradation were investigated. The racemization of L-lysine proceeded quantitatively at elevated temperatures. A sample of 1000 strains of bacteria, fungi, yeast and actinomyces were screened for the ability to degrade L-lysine asymmetrically. Microorganisms belonging to the Achromobacter, Agrobacterium, Candida, Comamonas, Flavobacterium, Proteus, Providencia, Pseudomonas and Yarrowia genera exhibited a high L-lysine-degrading activity. Comamonas testosteroni IAM 1048 was determined to be the best strain and used as a biocatalyst for eliminating the L isomer. The degradation rate of L-lysine with C. testosteroni IAM 1048 was influenced by pH, temperature and agitation speed. Under the optimal conditions, the L isomer in a 100-g/l mixture of racemic lysine was completely degraded within 72 h, with 47 g D-lysine/l left in the reaction mixture. Crystalline D-lysine, with a chemical purity greater than 99% and optical purity of 99.9% enantiomeric excess, was obtained at a yield of 38% from the reaction mixture by simple purification. An engineering analysis of L-lysine racemization and microbial degradation was carried out to establish the basis of process design for D-lysine production.