Discovery of a bifunctional acyltransferase responsible for ornithine lipid synthesis in S erratia proteamaculans

Summary Ornithine lipids ( OL s) are phosphorus‐free membrane lipids that can be formed by many bacteria but that are absent from archaea and eukaryotes. A function for OL s in stress conditions and in host–bacteria interactions has been shown in some bacteria. Some bacterial species have been described that can form OL s, but lack the known genes ( ols BA ) involved in its biosynthesis, which implied the existence of a second pathway. Here we describe the bifunctional protein OlsF from S erratia proteamaculans involved in OL formation. Expression of OlsF and its homologue from F lavobacterium johnsoniae in E scherichia coli causes OL formation. Deletion of OlsF in S . proteamaculans caused the absence of OL formation. Homologues of OlsF are widely distributed among γ‐, δ‐ and ε‐ P roteobacteria and in the C ytophaga ‐ F lavobacterium ‐ B acteroidetes group of bacteria, including several well‐studied pathogens for which the presence of OL s has not been suspected, such as for example V ibrio cholerae and K lebsiella pneumonia . Using genomic data, we predict that about 50% of bacterial species can form OL s.