Investigating a possible role for the bacterial signal molecules N‐acylhomoserine lactones in B alanus improvisus cyprid settlement

Increased settlement on bacterial biofilms has been demonstrated for a number of marine invertebrate larvae, but the nature of the cue(s) responsible is not well understood. We tested the hypothesis that the bay barnacle B alanus improvisus utilizes the bacterial signal molecules N‐acylhomoserine lactones ( AHL s) as a cue for the selection of sites for permanent attachment. Single species biofilms of the AHL ‐producing bacteria V ibrio anguillarum , A eromonas hydrophila and S ulfitobacter sp. BR 1 were attractive to settling cypris larvae of B . improvisus . However, when AHL production was inactivated, either by mutation of the AHL synthetic genes or by expression of an AHL ‐degrading gene (aiiA), the ability of the bacteria to attract cyprids was abolished. In addition, cyprids actively explored biofilms of E . coli expressing the recombinant AHL synthase genes luxI from V ibrio fischeri (3‐oxo‐C6‐ HSL ), rhlI from P seudomonas aeruginosa (C4‐ HSL /C6‐ HSL ), vanI from V . anguillarum (3‐oxo‐C10‐ HSL ) and sulI from S ulfitobacter sp. BR 1 (C4‐ HSL , 3‐hydroxy‐C6‐ HSL , C8‐ HSL and 3‐hydroxy‐C10‐ HSL ), but not E . coli that did not produce AHL s. Finally, synthetic AHL s (C8‐ HSL , 3‐oxo‐C10‐ HSL and C12‐ HSL ) at concentrations similar to those found within natural biofilms (5 μ m ) resulted in increased cyprid settlement. Thus, B . improvisus cypris exploration of and settlement on biofilms appears to be mediated by AHL ‐signalling bacteria in the laboratory. This adds to our understanding of how quorum sensing inhibition may be used as for biofouling control. Nonetheless, the significance of our results for larvae settling naturally in the field, and the mechanisms that underlay the observed responses to AHL s, is as yet unknown.