The Amino Acid Composition of Microorganisms

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Abstract
The quantities of 10 amino acids, namely, histidine, arginine, lysine, leucine, isoleucine, valine, methionine, threonine, phenylalanine, and tryptophane, were detd., microbiologi-cally, in the acid or alkaline hydrolyzates of the dried cells of Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Streptomyces griseus, Saccharomyces cerevisiae, Rhodotorula rubra, Rhizopus nigricans, Aspergillus niger, and PenicilHum notatum, grown under a variety of cultural conditions. It was found that the amino acid composition of an organism is, qualitatively and quantitatively, a stable and characteristic property of the cell under fixed conditions of growth. Although striking quantitative differences occur between microorganisms, the results, in general, emphasize the similarities rather than the differences in their amino acid composition. Certainly no fundamental differences, in that some amino acids are present in one organism but not in another, were encountered. The microbial proteins do not seem to differ materially from plant and animal proteins, represented by wheat and beef liver. Fungi contain 10-50% less, per unit of protein, of most of the amino acids detd. than do the other microbial groups. Mold mycelium prior to sporulation, compared to that after sporulation, contains considerably larger quantities of most of the amino acids, largely because of its 50% greater protein content. The mycelium and its spores, in general, have comparable amino acid contents. The quantities of individual amino acids in microorganisms may vary with the growth medium, aeration, and age of the cells.

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