The Response of Lactobacillus Casei to Partial Hydrolysates of Protein

It was observed in preliminary experiments that growth and acid production of Lactobacillus arabinosus 17-5 on a chemically defined medium(2) lacking isoleucine, leucine, or tryptophan were stimulated by partial hydrolysates of egg proteins directly in proportion to the degree of hydrolysis of the protein.Lactobacillus fermenti 36 (histidine, methionine, and threonine) and Leuconostoc mesenteroides P-60 (phenylalanine and lysine) responded similarly on the same medium lacking one of the indicated amino acids.On the other hand the stimulatory effect of the partial hydrolysates for Lactobacillus casei, grown on a medium lacking arginine or tyrosine, was greatly in excess of that produced by an equivalent amount of the pure amino acid.These investigations, extended as described in the experimental part, are of particular interest because of their possible relation to strepogenin.EXPERIMENTAL Hydrolysis of Proteins-A mixture containing about 5 gm. of casein' or of crystalline bovine plasma albumin2 and 50 ml. of 0.5 N HCl was refluxed for 6 hours.The hydrolysate was cooled, brought to pH 7.0 with NaOH, diluted to 250 ml. in a volumetric flask, and stored under toluene in the refrigerator.The hydrolysis was about 20 per cent complete, according to calculation by means of the formula % hydrolysis = y.amino N in partial hydrolysate -y.amino N in protein '% amino N in complete hydrolysate -y.amino N in protein * Paper 62.For Paper 61, see Rockland and Dunn (1).This work has been aided