Regulation of Chlamydia psittaci (Strain Guinea Pig Inclusion Conjunctivitis) Growth in McCoy Cells by Amino Acid Antagonism

Abstract

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 Chlamydia psittaci 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.

Intracellular Tryptophan Pool Sizes May Account for Differences in Gamma Interferon-Mediated Inhibition and Persistence of Chlamydial Growth in Polarized and Nonpolarized Cells

“…Chlamydial infection did not affect the tryptophan transport rates into polarized or nonpolarized cells, suggesting that the size of intracellular soluble tryptophan pools may be an important factor in chlamydial growth modulation. This finding agrees with that of previous studies examining nutritional requirements for chlamydial growth which indicated that intracellular amino acid pools of the host cell were sufficient for C. psittaci growth since changes in extracellular amino acid concentrations could not be detected (11).…”

The immunobiology and immunopathology of chlamydial infections

“…Transfer from overt to covert infection was a penicillin-sensitive multiple-step process dependent on host cell density and nutrition (1 15). Other factors possibly favouring persistent infection include the action of penicillin, gamma-interferon (IFNy) (12), other products of cell-mediated immunity (13), and the deprivation of the amino acids tryptophan and cysteine essential for chlamydial replication (31,32). Isolates of C. pecorum from sheep faeces seem to spontaneously produce persistent infection of cell cultures in vitro, failing to produce inclusions on serial passage in cycloheximide-treated monolayers for several weeks (1 28).…”

Chlamydial Development Is Adversely Affected by Minor Changes in Amino Acid Supply, Blood Plasma Amino Acid Levels, and Glucose Deprivation

“…The organisms obtain highenergy and biosynthetic metabolites, such as ATP and amino acids (AAs), from the host cell. Earlier studies in vitro have demonstrated that the chlamydial developmental cycle is grossly disrupted by removal of all or single AAs from growth medium (1,2,11,12). In particular, abnormally large chlamydial organisms were observed inside small inclusions; these had negligible infectivity (12).…”

“…In AA deprivation studies, media were composed of Earle's salts supplemented with vitamins to concentrations in MEM and the 13 MEM AAs (Sigma tissue-culture grade [11]) at concentrations of 100, 75, 40, 25, and 0%. Glucosedeficient medium was CMEM without glucose but including MEM nonessential AAs (a 100 M concentration of each; Gibco).…”