Genes required for the formation of virulence-provoking bacterial sphingolipids

Sphingolipids are ubiquitous in membranes of eukaryotes and are associated with important cellular functions. Although sphingolipids occur scarcely in bacteria, for some of them they are essential and, in other bacteria, they contribute to fitness and stability of the outer membrane, such as in the well-studied α-proteobacterium Caulobacter crescentus. We previously defined five structural genes for ceramide synthesis in C. crescentus . However, other mutants affected in genes of this same genomic region show cofitness with a mutant deficient in serine palmitoyltransferase. Here we show that at least two phospho-sphingolipids are produced in C. crescentus and that at least another six gene products are needed for the decoration of ceramide upon phospho-sphingolipid formation. All eleven genes participating in phospho-sphingolipid formation are also required in C. crescentus for membrane stability and for displaying sensitivity towards the antibiotic polymyxin B. The genes for the formation of complex phospho-sphingolipids are also required for C. crescentus virulence on Galleria mellonella insect larvae. Author Summary Sphingolipids participate in the formation of biological membranes and molecular signaling in higher organisms. Many bacteria also accommodate sphingolipids in their membranes. Here we report that eleven genes participate in the synthesis of complex bacterial phospho-sphingolipids. Our data show that these lipids contribute to membrane stability, but also confer sensitivity towards certain antibiotics. The bacterium Caulobacter crescentus is widely distributed in fresh water lakes and streams and was considered to be non-virulent. However, we demonstrate that complex phospho-sphingolipids are the main virulence contributors in this bacterium. ### Competing Interest Statement The authors have declared no competing interest.