The Bacterial Basis of Biofouling: a Case Study

Abstract

<span style="font-size:9.0pt;font-family: " times="" new="" roman";mso-fareast-font-family:calibri;mso-bidi-font-family:"times="" roman";="" mso-ansi-language:en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="" lang="EN-US">For billions of years bacteria have profusely colonized all parts of the oceans and formed biofilms on the benthos. Thus, from their onset, evolving marine animals adapted to the microbial world throughout their life cycles. One of the major adaptations is the use of bacterial products as signals for recruitment by larvae of many species in the seven invertebrate phyla that make up most of the biofouling community. We describe here investigations on the recruitment biology of one such species, the circum-tropical serpulid polychaete <i style="mso-bidi-font-style:normal">Hydroides elegans.</i> Insights gained from in-depth studies on adults and larvae of <i style="mso-bidi-font-style:normal">H. elegans</i> include: apparently constant transport of these biofouling worms on the hulls of ships maintains a globally panmictic population; larvae complete metamorphosis with little or no <i style="mso-bidi-font-style:normal">de novo</i> gene transcription or translation; larvae of this tube-worm settle selectively in response to specific biofilm-dwelling bacterial species; and biofilms provide not only a cue for settlement sites, but also increase the adhesion strength of the settling worms’ tubes on a substratum. Although biofilm-bacterial species are critical to larval-settlement induction, not all biofilm elements are inductive. Because studies on chemoreception systems in the larvae failed to find evidence for the presence of common chemoreceptors, we focused on the bacterial cues themselves. To do this, we studied a widely distributed and strongly inductive biofilm bacterium, <i style="mso-bidi-font-style:normal">Pseudoalteromonas luteoviolacea</i>. Using molecular manipulations of its genome, we learned that it produces complex clusters of bacteriocins, multi-protein structures evolutionarily derived from phage-tail elements, which induce metamorphosis of <i style="mso-bidi-font-style:normal">H. elegans</i>. But large questions remain: how do these complex structures bring about induction? Do larvae of other invertebrate species that settle in response to <i style="mso-bidi-font-style: normal">P. luteoviolacea</i> also metamorphose in response to its bacteriocins? Do all inductive bacterial species produce bacteriocins? As a whole, the described studies on the recruitment of <i style="mso-bidi-font-style:normal">Hydroides elegans</i> demonstrate the importance of in-depth investigations of model species for understanding the problem of biofouling as well as the ubiquity of essential animal-bacterial interactions in the sea.</span>