Growth-Factors for Propionic and Lactic Acid Bacteria

Abstract

Wood, et at., 1 and Tatum, et al., 2 showed that an ether-soluble acid (obtained from yeast-extract, potato-extract or corn-steep) and vitamin B₁ stimulate growth of the propionic acid bacteria. Snell, et al., 3 have shown that ether-extract of potato stimulates Lactobacillus delbrückii but an additional factor present in peptone is essential for their growth in hydrolyzed casein, tryptophane and glucose medium.

In the present investigation we have continued this study, particularly in determining the effect of lactoflavin on growth. Lava, et al., 4 fractionated yeast-extract and found the portion which contained B₂ was the most active. They suggested that flavin or B₂ might be a stimulant for the propionic acid bacteria but were unable to prove this because of the impurity of their B₂ preparation and lack of a basal medium free of B₂.

We have tested the activity of lactoflavin by adding it to a basal medium which contained per 100 cc. (1) ether-extract of 3 gm. of yeast-extract, (2) 1.0 gamma B₁ (Merck's crystalline), (3) 0.3 gm. (NH₄)₂SO₄, (4) 0.6 gm. NaOAc, (5) 1.0 gm. glucose, (6) inorganic salts. In this medium most propionic acid bacteria failed to grow after the 4th transfer. Addition of hydrolyzed casein or a mixture of purified amino acids gave consistently good growth throughout numerous transfers with all cultures tested (11W, 34W, 39W, 52W, 53W, 49W).

Crystalline lactoflavin was added to the basal medium in concentration equivalent to 0.00, 0.01, 0.05, and 0.20 mg. per 100 cc. of medium; 5 cc. amounts of medium were inoculated with one drop of a suspension of cells grown on yeast-extract medium. Transfers were made after 3 days' growth at 30°C. and the acid was titrated after incubation for 5 days. The stimulation produced by lactoflavin was evident on the first transfer ibut by repeated transfer the results were more distinct.