Cystine Axi) Related Compoupu’ds in the Nutrition of Lactic Acid Bacteria*

The metabolism of certain inorganic forms of sulfur by various autotropic bacteria has been studied extensively in the past. However, investigations dealing with the metabolism of sulfur compounds by the heterotropic bacteria have not been numerous. Such work as has been done (reviewed by Meyers and Porter (1)) indicates that these microbial systems may be quite specific in their requirements for sulfur, especially for organic forms of sulfur. It was not until the development of microbiological assays for amino acids that the exacting requirements of lactic acid bacteria for these nitrogenous substances became apparent. Indications that cystine might be required by several lactic acid bacteria mere evident from the work of Wood, Geiger, and Werkman (2) in 1940. Later, Hutchings and Peterson (3) showed that cystine is required in a complete medium for Lactobacillus casei e. Shankman, Dunn, and Rubin (4), however, reported that they could not obtain reproducible standard curves for cystine with this organism. Shankman (5) and Hegsted (6) demonstrated the requirement for cystine by L. arabinosus 17-5; assays for cystine with this organism have been proposed by Shankman, Dunn, and Rubin (4) and by Barton-Wright (7). The absolute requirement of cystine by L. arabinosus, however, could not be confirmed in this laboratory (unpublished data). According to Dunn et al. (8), cystine is required by Leuconostoc mesenteroides PD-60 but was found to be unessential for Lactobacillus fermenti (9). In experiments by Greenhut, Schweigert, and Elvehjem (lo), Streptococcus faecalis R grew only slightly on a chemically defined medium free from cystine; later work in this laboratory indicates that cyst,ine is merely stimulatory to the growth of this organism.