Pseudovibriamides fromPseudovibriomarine sponge bacteria promote swarming motility via transcriptional modulation

Abstract

AbstractPseudovibrioα-Proteobacteria have been repeatedly isolated from marine sponges and proposed to be beneficial to the host. Bacterial motility is known to contribute to host colonization. We have previously identified pseudovibriamides A and B, produced in culture byPseudovibrio brasiliensisAb134, and shown that pseudovibriamide A promotes flagellar motility. Pseudovibriamides are encoded in a hybrid nonribosomal peptide synthetase-polyketide synthase gene cluster that also includes several accessory genes. Pseudovibriamide A is a linear heptapeptide and pseudovibriamide B is a nonadepsipeptide derived from pseudovibriamide A. Here we define the borders of the pseudovibriamides gene cluster, assign function to biosynthetic genes using reverse genetics and test the hypothesis that pseudovibriamides impact motility by modulating gene transcription. RNA-seq transcriptomic analyses of strains having different compositions of pseudovibriamides suggested that both pseudovibriamides A and B affect genes potentially involved in motility, and that a compensatory mechanism is at play in mutants that produce only pseudovibriamide A, resulting in comparable swarming motility as the wild type. The data gathered suggest that pseudovibriamides A and B have opposite roles in modulating a subset of genes, with pseudovibriamide B having a primary effect in gene activation, and pseudovibriamide A on inhibition. Finally, we observed many differentially expressed genes (up to 29% of the total gene number) indicating that pseudovibriamides have a global effect on transcription that goes beyond motility.ImportanceMarine sponges are found throughout the oceans from tropical coral reefs to polar sea floors, playing crucial roles in marine ecosystems.Pseudovibriobacteria have been proposed to contribute to sponge health. We have previously shown that pseudovibriamides produced byPseudovibrio brasiliensispromote bacterial motility, a behavior that is beneficial to bacterial survival and to host colonization. The gene cluster that encodes pseudovibriamide biosynthesis is found in two thirds ofPseudovibriogenomes. This gene cluster is also present inPseudomonasbacteria that interact with terrestrial plants and animals. Here we first assign function to pseudovibriamide biosynthetic genes using reverse genetics. We then show that pseudovibriamides play a major role in transcriptional regulation, affecting up to 29% ofP. brasiliensisgenes, including motility genes. Thus, this work gives insights into pseudovibriamide biosynthesis and provides evidence that they are signaling molecules relevant to bacterial motility and to other yet to be identified phenotypes.