The marine bacterium Alteromonas espejiana induces metamorphosis of the hydroid Hydractinia echinata

Abstract

The marine hydroid Hydractinia echinata develops into a primary polyp from a planula larva stage. The planula does not undergo metamorphosis in sterile filtered seawater. Metamorphosis is induced by certain bacteria occurring, as a rule, on the shells of molluscs inhabited by hermit crabs of the genus Eupagurus. Bacteria were isolated from shells occupied by H. echinata, and bacterial clones were selected which had a strong potency for inducing metamorphosis in planula larvae. One such clone was further subcloned for strong metamorphosis-inducing potency and finally investigated for inductive characteristics and for identification purposes. The bacterium is a motile, aerogen, gram-negative rod with a polar flagellum. It was identified on the basis of several physiological characteristics as a strain of the genus Alteromonas espejiana. The ability to induce metamorphosis might not be restricted to A. espejiana. The inhibitor of protein kinase C, sphingosine, inhibited metamorphosis induced by A. espejiana. The metamorphosis-inducing principle is likely to be a lipid, since upon lipid extraction and separation of different lipid classes by solid phase extraction on silica-aminopropyl columns a metamorphosis-inducing fraction was obtained.