Interrelationships between Amino -acids in the Growth of Coliform Organisms

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Abstract
SUMMARY: Three hundred and fifty-six strains of Bacterium coli, which were capable of growing on a simple salt medium containing ammonia as sole nitrogen source and glucose, were tested for inhibition of growth by added amino-acids. Inhibitions by certain amino-acids were found, and each inhibition could be prevented by the simultaneous presence of one or more other amino-acids. It was not possible to correlate these inhibitions with any other biochemical property of the strains. There was, however, a remarkably high proportion of serine-inhibited strains amongst those which had been isolated from cases of infantile gastro-enteritis. There are numerous reports in the literature concerning the inhibitory effects of naturally occurring amino-acids on the growth of various organisms under special conditions. A classic example is the study by Gladstone (1939) of the growth of several Bacillus anthracis strains in defined amino-acid media; when leucine or valine separately were added in concentrations as low as 1 pg./ml. growth did not occur; when both amino-acids were simultaneously present or were both absent the organisms grew well. Porter & Meyers (1945) described the inhibition of Proteus morganii growing in a chemically-defined medium, by threonine, norvaline or norleucine ; several amino-acids prevented the effects of the two former but only methionine consistently prevented the norleucine inhibition. The inhibition of one strain of Bacterium coli by D-serine in amounts of the order of 5 pg./ml. was described by Davis & Maas (1949); this effect was wholly preventable by glycine or alanine and partly by histidine and leucine. These authors investigated some of the characteristics of the inhibition, and reported that it was mainly an increase up to 48 hr. in the lag period; bacteria which grew up after this time were just as sensitive as the originals. It was, however, possible to pick serine- resistant mutants, the proportions of which were increased by ultraviolet irradiation. In spite of the numerous instances of microbial inhibition by amino-acids, a survey of such inhibitions within any one species has not been made. Such a survey would indicate whether these inhibitions are common to all strains of the given species and whether any differences observed might be correlated with other biochemical properties of the different strains. It has already been reported (Tatum, 1949; Rowley, 1953) that the K12 strain of Bad. coli when growing on the minimal medium of Davis & Mingioli (1950) was completely inhibited by as little as 0.5 pg./ml. of DL-valine, and that this effect was reversed by the simultaneous presence of leucine or isoleucine. A collection has now been made of 356 strains of Bact. coli, and each of these has been

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