Meeting Abstract
The serpulid polychaete Hydroides elegans is an excellent model organism for studies of larval settlement and metamorphosis in response to bacterial biofilms. However, despite 25 years of study, aspects of attachment and morphogenesis remain confused. In current research, detailed observations of larvae were made from the moment of contact with: a natural biofilm; a monospecific biofilm of the bacterial species Pseudoalteromonas luteoviolacea; and an active extract of the same bacterium. Prior studies have shown that these larvae do not detect a natural biofilm by the presence of dissolved substances, and must contact a biofilm before metamorphosis is initiated. When observed under controlled conditions, after contact with a natural biofilm or a biofilm of P. luteoviolacea alone, larvae explore the biofilm for up to 10 min, stop moving, and secrete a primary organic tube, which anchors them longitudinally on the substratum. Only minutes later, compound cilia of the prototroch are resorbed, and metatrochal cilia are shed. Then, still within the first 25 min. of biofilm contact, the double row of ciliated cells that lines the food groove is shed in small clusters, most of which are eaten by the larva. The result of all this loss is the creation of a deep groove separating the trunk, just anterior to the collar, from the head region. Interestingly, when larvae are treated with a cell-free extract from P. luteoviolacea the natural order of metamorphic events is disturbed, so that trochal cilia disappear prior to primary tube formation. Clearly, were this sequence to occur in the real world, the larvae would lose their ability to move about without the anchoring stability of the primary tube, and be blown away by turbulent water flow.
