Early intracellular trafficking of Waddlia chondrophila in human macrophages

Abstract

Waddlia chondrophilais an obligate intracellular bacterium considered as a potential agent of abortion in both humans and bovines. This member of the orderChlamydialesmultiplies rapidly within human macrophages and induces lysis of the infected cells. To understand how thisChlamydia-like micro-organism invades and proliferates within host cells, we investigated its trafficking within monocyte-derived human macrophages. Vacuoles containingW. chondrophilaacquired the early endosomal marker EEA1 during the first 30 min following uptake. However, the liveW. chondrophila-containing vacuoles never co-localized with late endosome and lysosome markers. Instead of interacting with the endosomal pathway,W. chondrophilaimmediately co-localized with mitochondria and, shortly after, with endoplasmic reticulum- (ER-) resident proteins such as calnexin and protein disulfide isomerase. The acquisition of mitochondria and ER markers corresponds to the beginning of bacterial replication. It is noteworthy that mitochondrion recruitment toW. chondrophilainclusions is prevented only by simultaneous treatment with the microtubule and actin cytoskeleton-disrupting agents nocodazole and cytochalasin D. In addition, brefeldin A inhibits the replication ofW. chondrophila, supporting a role for COPI-dependent trafficking in the biogenesis of the bacterial replicating vacuole.W. chondrophilaprobably survives within human macrophages by evading the endocytic pathway and by associating with mitochondria and the ER. The intracellular trafficking ofW. chondrophilain human macrophages represents a novel route that differs strongly from that used by other members of the orderChlamydiales.