Host cell-derived sphingolipids are required for the intracellular growth of Chlamydia trachomatis

Chlamydia trachomatis, an important cause of human disease, is an obligate intracellular bacterial pathogen that relies on the eukaryotic host cell fo r its replication. Recent reports have revealed that the C. trachomatis vac uole receives host-derived sphingolipids by fusing with trans-Golgi network (TGN)-derived secretory vesicles. Here, it is shown that these lipids are required for the growth of the bacteria. C. trachomatis was unable to repli cate at 39 degreesC in the Chinese hamster ovary (CHO)-derived cell line SP B-1, a cell line incapable of synthesizing sphingolipids at this temperatur e because of a temperature-sensitive mutation in the serine palmitoyltransf erase (SPT) gene. Complementation with the wild-type SPT gene or addition o f exogenous cell-permeable sphingolipid precursors to the mutant cells rest ored their ability to support chlamydial replication. L-cycloserine (L-CS) and fumonisin B-1 (FB1), inhibitors of sphingolipid biosynthesis, decreased the proliferation of the bacteria in eukaryotic cells at concentrations th at also decreased host cell sphingolipid synthesis. In the case of FB1, the vacuoles appeared aberrant; the addition of sphingolipid precursors was ab le to reverse the altered morphology of the FB1-treated vacuoles. Collectiv ely, these data strongly suggest that the growth and replication of chlamyd iae is dependent on synthesis of sphingolipids by the eukaryotic host cell and may contribute to this organism's obligate intracellular parasitism.