Enantioselective catabolism of racemic serine: preparation of d-serine using whole cells of Fusobacterium nucleatum

Abstract

Incubation of racemic serine with the anaerobic bacterium Fusobacterium nucleatum yielded d-serine in high enantiomeric excess (>95%). Selective degradation of the l-amino acid was most efficient when F. nucleatum was resuspended in a buffer at high cell densities (ca. 50–100 g damp cells/L); a single incubation effectively removed almost all l-serine from racemic mixtures at initial concentrations up to 800 mM, the solubility limit. The product d-amino acid was separated from the metabolic en d-products (acetate, butyrate and lactate) and buffer components by a single cation-exchange step. After recrystallization, 83% of the d-serine in the initial racemate was recovered with >99% ee (HPLC) and 98% purity (HPLC). This anaerobic microbial approach provides a viable complementary method for generating d-serine, a valuable chiral starting material for chemical synthesis.