Bacteria synthesize numerous types of sphingolipids with various physiological functions. Despite their roles in mediating host inflammation, cellular differentiation, and protection from environmental stress, their biosynthetic pathway remains undefined since several essential eukaryotic ceramide synthesis enzymes have no bacterial homologue. Using genetic and biochemical approaches, we identified the complete pathway for bacterial ceramide synthesis. Bioinformatic and phylogenetic analyses revealed the presence of these genes in a broad range of bacterial taxa and led to our discovery of the first Gram-positive species to produce ceramides. Biochemical experiments with purified proteins support a model in which the bacterial pathway operates in a different order than in eukaryotes. Furthermore, phylogenetic analyses are consistent with the independent evolution of the bacterial and eukaryotic ceramide pathways. Current work is being done to elucidate the specific subcellular localization of the synthetic enzymes and identify additional proteins required for the transport of sphingolipids to the outer membrane of Gram-negative bacteria.
Funding was provided by National Science Foundation grants MCB-1553004 and MCB-2031948 (E.A.K.), National Institutes of Health grants GM069338 and R01AI148366 (Z.G.), and Biotechnology and Biological Sciences Research Council grants BB/M010996/1 and BB/T016841/1 (D.J.C.).
