Ctenophore ingestion rates are linearly related to food density up to concentrations much higher than those usually assumed to be representative of the natural environment. Daily rations in excess of l,OOO% of their body weights at high prey densities are matched by growth rates characteristic of phytoplankton (daily doublings). Digestive efficiencies >70% were recorded at moderate prey densities. Growth efficiencies rarely exceed 10% bccausc the bulk of assimilated food (up to 80% of that ingested) is required for the energy metabolism of these organically dilute (carbon 2% of dry wt) creatures.

Plasmid pJM1 from an invasive strain of Vibrio angiuillarum mediates an ironsequestering system that is associated with the ability of this bacterium to cause septicemia in marine fishes. This plasmid-mediated iron uptake system was analyzed by using mutations caused by transposon Tnl. Restriction endonuclease analysis of iron uptake-deficient and-proficient derivatives generated by insertion of Tnl and molecular cloning experiments permitted us to localize the plasmid regions involved in the process of iron sequestration to a stretch of about 20 kilobase pairs. In addition, the existence of two plasmid-mediated components involved in the process of iron uptake in V. anguillarium was defined: a diffusible substance which functions as a siderophore and a nondiffusible receptor for complexes of iron-siderophore, which we have tentatively identified as the pJM1 plasmid-mediated outer membrane protein OM2 of V. angiuillarium.

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