Studies in Bacterial Nutrition

Abstract

By treatment with 66% and then with 86% alcohol, a tryptic digest of caseinogen was separated into 3 fractions: 2 precipitates, A and B (both soluble in water), and a residual liquid, C. The fractions were freed from alcohol and redissolved in water. All the inorganic phosphate was present in A; B and C contained phosphate in organic combination. Singly, none of the fractions showed marked growth when sown with streptococci; a combination of all 3 gave growth equal to that in the original broth. A+C also gave almost as good growth as the control, but B+C showed a 24-hr. lag. When disodium phosphate (p H 7.5) was added to the different combinations, A + C gave no growth, while B+C gave as good growth as the control in 24 hrs. No inhibition occurred in B+C even if the phosphate concentration was made much higher than in A+C. A+B gave slight growth in the presence or absence of added phosphate. The deterioration and darkening of caseinogen broth from prolonged steaming are probably due to presence of phosphate, which seems to cause inactivation of a growth factor for streptococci. This factor is associated with the simpler protein derivatives.