UNIDENTIFIED GROWTH FACTOR FOR A LACTIC ACID BACTERIUM.

Weinman, Donald E. (University of Georgia, Athens), George K. Morris, and William L. Williams. Unidentified growth factor for a lactic acid bacterium. J. Bacteriol. 87:263-269. 1964.-Lactobacillus bulgaricus Georgia strain required an unidentified growth factor, named Georgia bulgaricus factor (GBF), when grown on a semisynthetic basal medium. Aqueous extracts of torula yeast and beef liver were the best sources of GBF. Adenine, ribonucleic acid (RNA), alkaline digests of RNA, and Mg(++) also stimulated growth, but to a considerably lesser extent than liver and yeast extracts. Several purines, pyrimidines, and related compounds also promoted growth responses in individual experiments, but not consistently. Intact deoxynucleic acid (DNA), deoxyadenylic acid (dAMP), and deoxyguanylic acid (dGMP) inhibited growth. The DNA and dAMP inhibitions were fully reversed by crude sources of GBF, while dGMP inhibition was only partially reversed. RNA reversed DNA inhibition to a small extent. GBF was stable to heat at pH 2.5 to 11 and to prolonged light exposure. It was destroyed by heating at pH 1.0. The GBF activity moved as a single component in paper chromatography. It was firmly adsorbed on charcoal and poorly soluble in organic solvents. A concentrate, 28 times more potent than liver extract, was prepared by prolonged paper chromatography. All known growth factors and biological compounds readily available were assayed for GBF activity, none of which gave a response similar to the crude extracts. Final proof that a new growth factor exists must await definite identification of the active compounds.