(1) All the DL-forming lactic acid bacteria used in this research, i.e., Lactobacillus plantarum (2 strains), L. arabinosus, L. japonicus, L. brevis, and Pediococcus hennebergi, demand nicotinic acid as an essential growth factor, while organic bases such as purines and pyrimidines are not essential for these strains.
(2) If DL-formers are cultured in a medium which is limited in nicotinic acid, the resulting lactic acid reveals measurable optical activity. This is caused by the suppression of the formation of co-racemiase, DPN, by the insufficiency of its precursor.
(3) By determining the optical forms of lactic acid thus formed, DL-formers can be divided into D- and L-fomers. This fact is considered fundamental from the standpoint of natural systematics.