Trophic transfer of Fe, Zn and Am from marine bacteria to a planktonic ciliate

Marine bacteria may serve as an enriched source of essential and non-essential metals for animals that eat them. We evaluated this trophic transfer by measuring the accumulation of Fe, Zn and Am by planktonic ciliates (Uronema sp.) following the ingestion of radiolabeled heterotrophic bacteria (Vibrio natriegens) in laboratory experiments. V. natriegens cells were allowed to accumulate 55 Fe, 65 Zn and 241 Am from seawater for 5 d and were subsequently fed to the ciliates. Uptake and depuration of the metals was monitored in the ciliates over time. Measured assimilation efficiencies were 79% for Fe, 29% for Zn and 24% for Am; corresponding efflux rates were 0.1 d -1 for Fe, 0.9 d -1 for Zn and 0.7 d -1 for Am. These results suggest that bacteria present an alternate source to phytoplankton for some metals (especially Fe) to be introduced into metazoan food webs.