  Nitrogen isotopic hetero- and homogeneity of D-{\alpha}-alanine and
L-{\alpha}-alanine were investigated in microbial processes in the domain
Bacteria and in chemical processes in symmetric organic synthesis. D-alanine is
an enantiomer that is physiologically essential for microbial growth and
metabolic maintenance. The nitrogen isotopic difference {\Delta}15ND-L (defined
as {\delta}15ND-Ala - {\delta}15NL-Ala) in peptidoglycan amino acids in
bacteria such as the representative gram-positive phyla Firmicutes and
Actinobacteria (Enterococcus faecalis, Staphylococcus aureus, Staphylococcus
staphylolyticus, Lactobacillus acidophilus, Bacillus subtilis, Micrococcus
luteus, and Streptomyces sp.) tended to be 15N-depleted in D-alanine
({\Delta}15ND-L < -2.0 permil). These results suggest that the composition of
isotopically heterogeneous components in these bacteria is primarily controlled
by enzymatic pathways prior to formation of the bacterial cell wall. In
contrast, the {\Delta}15ND-L of racemic alanine in the chemical pathway during
the nucleophilic substitution reaction (SN1 type) between 2-bromopropionic acid
and ammonia identified fully homogeneous components for each enantiomer. The
novel enantiomer-specific isotopic analysis (ESIA) method is useful in
determining the origins of chirality in biogenic and abiogenic processes and is
applicable to enantiomer studies.
  -- Keywords: D-alanine, microbial process, chemical process, nitrogen
isotopic composition, enantiomer-specific isotope analysis (ESIA)
