Understanding settlement: the role of common bacterial biofilm elements in the induction and metamorphosis of the polychaete Hydroides elegans
Many benthic marine invertebrates are induced to settle and metamorphose as a result of interactions with bacterial biofilms. The identity of the cues that mediate these interactions, however, remain largely unknown. The serpulid polychaete Hydroides elegans is an excellent model organism for studies of larval settlement and metamorphosis in response to bacterial biofilms. Detailed investigations into the nature of the settlement cue produced by the bacterium Pseudoalteromonas luteoviolacea have previously established bacteriocin aggregates (or MACs) as the metamorphic cue. However, H. elegans can be induced to settle and metamorphose by a number of bacteria that do not produce MACs. An additional cue capable of inducing settlement in this species are associated with outer membrane vesicles (OMVs) produced by the bacterium Cellulophaga lytica. OMVs are produced ubiquitously by Gram negative bacteria and have been observed to mediate numerous interactions between bacteria and Eukaryotes including, but not limited to, cell-cell signalling, antibiotic resistance and virulence. The chemical composition of OMVs can be highly variable between species and can be composed primarily of proteins, phospholipids, lipopolysaccharide. OMVs from some bacteria include genetic material and or virulence factors. In this study we use enzymatic tests including DNase, RNase, Proteases and Lipases as well as chemical purification techniques to determine the component of these complex structures involved in the induction of metamorphosis in H. elegans. We show that induction of metamorphosis in H. elegans can be induced by a common bacterial component. The widespread presence and variation of this compound may explain the induction of metamorphosis of H. elegans by multiple bacterial biofilm species and improve our understanding of the role of biofilm bacteria in the induction of settlement in marine invertebrate larvae.