ABSTRACT
The behavior and development of many animals can be modified by bacteria. One of the most widespread instances of this is the regulation of metamorphosis by marine invertebrates. In many instances, marine larvae are totally dependent upon the detection of bacterial cues for their development and progression into adult forms. Yet, little is known of the diversity of bacteria that induce larvae to settle, and even less of the cues they produce. Larvae of the serpulid polychaete Hydroides elegans are induced to metamorphose by specific bacterial strains that reside within complex biofilm communities. Single-strain biofilms of the flavobacterium Cellulophaga lytica are strongly inductive, and lipopolysaccharides (LPS) isolated from this bacterium appear to act as the relevant metamorphic cue for larvae of H. elegans. LPS is an important Microbe-Associated Molecular Pattern, whose detection is entirely context dependent and may reflect the presence of a pathogen or beneficial microbe. In light of the prevalence of beneficial and benign interactions with bacteria, examining the pre-symbiotic dealings between Eukaryotes and bacteria may increase our understanding of the evolution of both facultative and obligate symbiotic relationships among animals and microbes.
