STUDIES ON THE PROTEOLYTIC BACTERIA OF MILK IV. ACTION OF PROTEOLYTIC MILK BACTERIA ON AMINO ACIDS AND OTHER SIMPLE NITROGENOUS COMPOUNDS

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Abstract
Two hundred and twenty-nine cultures of proteolytic organisms from milk were inoculated into synthetic media containing various simple nitrogenous compounds as a sole source of N, and growth, increase in NH3 and change in pH were noted. The nitrogenous compounds included sodium ammonium phosphate, ammonium succinate, urea, asparagine, and the following amino acids: glycine, alanine, leucine; aspartic acid, glutamic acid, tryptophan and tyrosine. Some of the organisms which can use urea as a sole source of N cause an alkaline reaction due to liberation of NH3; others cause an acid reaction and apparently liberate no free NH3. Organisms which can use NH3 as a sole source of N can apparently use any of the simpler amino acids if the medium contains a fermentable sugar as a source of C. In media containing no sugar or similar C compounds and in which the amino acid has to serve as a source of both C and N, results are obtained which may be useful in grouping the organisms. The proteolytic bacteria can be differentiated into groups on the basis of their growth and action on sugar media containing NH3 or urea as their only source of N, and on media containing ammonium succinate, asparagine or various amino acids as a sole source of both C and N.

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