Amino Acids Required by the Diphtheria Bacillus for Growth

Abstract

The writer 1 described experiments indicating that a strain of diphtheria bacillus under investigation required for its growth, among other things, a substance associated with the “proline” fraction of amino acids obtained by Dakin's butyl alcohol extraction method. Further work with this material has shown that not a single factor, but 3 separate substances were involved in the accelerating effect there described. It was learned to begin with, that the action was not entirely limited to the “proline” fraction, but that the “monoamino” fraction even more frequently exerted it, and occasionally the 2 added together gave better results.

Before any material progress was made in separating and recognizing these factors, it became necessary to introduce a quantitative method for the estimation of relative amounts of growth. The method finally used was a micro kjeldahl determination of the amount of nitrogen in the bacterial growth on a measured amount of material for a definite time. The details of this procedure will be described elsewhere.

Careful examination of the effect produced by the proline fraction showed that proline itself was evidently not concerned, but that the acceleration in growth was apparently produced by minute quantities of ethyl alcohol used as solvent in handling the fraction. Pure ethyl alcohol exerted the same effect, and maximum acceleration of growth with our particular strain of organism is reached with a concentration of about 0.5%. Larger quantities of course become inhibitory. In place of ethyl alcohol, sodium acetate, glycerol, or maltose all appear to enhance the growth when added to the same control solutions.