Isoleucine and Valine Metabolism of Escherichia Coli

In the preceding publication (1) mention has been made of the syntrophism existing between the mutant strains llA16 and 2OA19 of Escherichia COG. These mutants, requiring isoleucine and isoleucine plus valine respectively, were able to grow together on a minimal agar plate, free of amino acids, which would not support the growth of either mutant alone. The nature of this syntrophism forms the subject of the present communication. The culture fluids of strain llA16 were found to be markedly inhibitory to the parent strain K-12, but this inhibition could be overcome by the addition of isoleucine. When the test for inhibition was carried out auxanographically by placing a disk of filter paper saturated with the strain llA16 culture fluid on a minimal agar plate seeded with strain K-12, a clear zone of inhibition was found to surround the paper disk; however, inside this zone, close to the paper disk, a reversal of the inhibition could be observed. Similar experiments in which the isoleucineand valine-requiring mutant, 2OA19, was used in place of strain K-12 indicated a zone of growth of the mutant corresponding to the zone in which the inhibition of strain K-12 had been reversed in the previous experiment. These observations indicated that compounds having biological effects similar to valine and isoleucine were accumulating in culture fluids of strain llA16. In preliminary experiments carried out in an attempt to .determine the chemical nature of these compounds and to develop pro-