SUMMARY: Chlamydiae have amino acid requirements for growth in tissue culture as defined by those amino acids whose individual omission from the growth medium prevents chlamydial multiplication. We have tested the hypothesis that this inhibition of growth arises as a result of antagonism between particular amino acids such that inhibition occurs when the concentration of one amino acid is reduced in the presence of the antagonist amino acid at high concentration. Using the strain guinea pig inclusion conjunctivitis (GPIC), in the presence of cycloheximide, the requirement for valine was abrogated by the simultaneous omission of isoleucine, that for phenylalanine by simultaneous omission of tryptophan and that for leucine by simultaneous omission of isoleucine plus valine. The antagonism shown between leucine and isoleucine plus valine appears to be unique among bacteria. In the absence of cycloheximide, GPIC had an additional need for tryptophan, tyrosine and isoleucine; these amino acid requirements were shown for both infected McCoy, HeLa and BHK cells. The results are consistent with a mechanism for regulation of parasite growth which depends on the balance of amino acid concentrations in the extracellular environment.


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