Biochemical stratagem for obligate parasitism of eukaryotic cells by Coxiella burnetii.

Abstract

The in vitro metabolism of glucose and glutamate by whole cells of C. burnetii under conditions designed to approximate the pH within the phagolyosome and the effect of manipulation of the phagolysosomal pH by lysosomotropic amines on the replication of C. burnetii in chicken embryo fibroblasts were examined. The transport, catabolism and incorporation of both glucose and glutamate were highly stimulated by acidic conditions; at pH 7.0 metabolism of these substrates was minimal. The transport processes were energy dependent and highly sensitive to inhibition by uncouplers of oxidative phosphorylation. Increasing the phagolysosomal pH of infected chicken embryo fibroblasts by use of the lysosomotropic agents chloroquine, methylamine or ammonium chloride inhibited the multiplication of C. burnetii, thus demonstrating the in vivo requirement for the acidic conditions of the phagolysosome. This apparent dependence upon phagosome-lysosome fusion to generate pH conditions favorable to C. burnetii replication suggests a unique biochemical mechanism of parasite activation. A pathogenic mechanism based on regulation of microbial metabolism by H+-dependent stimulation of cell function is proposed.