ThePseudomonas aeruginosa sphBCgenes are important for growth in the presence of sphingosine by promoting sphingosine metabolism

Abstract

AbstractSphingoid bases, including sphingosine, are important components of the antimicrobial barrier at epithelial surfaces where they can cause growth inhibition and killing of susceptible bacteria.Pseudomonas aeruginosais a common opportunistic pathogen that is less susceptible to sphingosine than many Gram-negative bacteria. Here, we determined that deletion of thesphBCDoperon reduced growth in the presence of sphingosine. Using deletion mutants, complementation, and growth assays inP. aeruginosaPAO1, we determined that thesphCandsphBgenes, encoding a periplasmic oxidase and periplasmic cytochrome c, respectively, were important for growth on sphingosine, whilesphDwas dispensable under these conditions. Deletion ofsphBCDinP. aeruginosaPA14,P. protegensPf-5, andP. fluorescensPf01 also showed reduced growth in the presence of sphingosine. TheP. aeruginosa sphBCgenes were also important for growth in the presence of two other sphingoid bases, phytosphingosine and sphinganine. In wild-typeP. aeruginosa, sphingosine is metabolized to an unknown non-inhibitory product, as sphingosine concentrations drop in the culture. However, in the absence ofsphBC, sphingosine accumulates, pointing to SphC and SphB as having a role in sphingosine metabolism. Finally, metabolism of sphingosine by wild-typeP. aeruginosaprotected susceptible cells from full growth inhibition by sphingosine, pointing to a role for sphingosine metabolism as a public good. This work shows that metabolism of sphingosine byP. aeruginosapresents a novel pathway by which bacteria can alter host-derived sphingolipids, but it remains an open question whether SphB and SphC act directly on sphingosine.