CHEESE-RIPENING STUDIES: Nitrogen Requirements of Lactic Acid Bacteria: I. THE FRACTIONAL ANALYSIS OF VARIOUS NITROGEN SOURCES USED FOR THE QUANTITATIVE DETERMINATION OF THE SUGAR-FERMENTING ABILITIES OF LACTIC ACID BACTERIA

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Abstract
A study is being made of the nitrogen requirements of lactic acid bacteria. Employing the method of Wasteneys and Borsook, the nitrogen distribution has been determined in nitrogen sources available commercially and in sources that may be readily prepared by laboratory workers. Forty-three sources have been analyzed. The results of the analyses show that peptic casein digest broth contains from 55 to 63% protein nitrogen, 19 to 25% peptone nitrogen, and 14 to 17% subpeptone nitrogen, according to the particular casein used—when the standard method of preparation is followed. If less casein is used for digestion, or if the period of digestion is reduced, the total amount of nitrogen made available is lower; this being true for the subpeptone nitrogen fraction in particular. In tryptic casein digest broth, 70% of the nitrogen is in the subpeptone nitrogen fraction, and about 28% is found as peptone nitrogen. The broth prepared from one commercial source presents a nitrogen distribution picture that is something of a composite of the nitrogen distribution in the standard casein digest and the tryptic casein digest.When the nitrogen sources fractionated are employed as the substrate for fermentation studies, it will be seen that whilst the suitability of a source is not always fully indicated by the nitrogen distribution picture, the biological significance of the nitrogen distribution in the sources is, on the whole, reflected in the influence on the sugar-fermenting abilities of the lactic acid bacteria reported upon.

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