Biosynthesis of D-Aspartic Acid by Streptococcus faecalis*

In biotin deficiency, aspartic acid becomes a limiting factor in the growth of Streptococcus faecalis ATCC 9190. Suboptimal concentrations of L-aspartate in biotin-deficient medium produce partial growth followed by lysis, which is typical of cell wall lysis due to depletion of an amino acid essential for cell wall biosynthesis. D-Aspartate, which is utilized by the cells with considerable less efficiency than the L isomer, can prevent depletion lysis when present at high concentrations. Irrespective of aspartate concentration, a minimal concentration of biotin is so indispensable for normal growth that at lower biotin concentrations partial growth occurs followed by cell lysis. L-AspartateJ4C included in the growth medium is incorporated into D-aspartate isolated from the cell wall. Dilution with endogenously synthesized amino acid is a function of aspartate and biotin concentrations. Wall and protein aspartic acids were isolated from cells grown with DL-aSpSrtate-l-r% or with DL-aspartate-4J4C and selectively decarboxylated with chloramine-T in alkali to locate the position of 14C in the molecule. Lack of randomization of 14C between the orand /3-carboxyl groups indicated the absence of a symmetrical intermediate with enzymically indistinguishable carboxyl groups (fumarate) in the pathway between Land D-aspartic acid. Cell wall D-aspartate isolated from cells grown on L-aspartateJ6N contained nearly the same 16N content as the r,-aspartate in the medium, indicating that D-aspartate is formed from L-aspartate via racemization.