Adsorption and precipitation of iron from seawater on a marine bacteriophage (PWH3A-P1)

The distribution and chemical form of iron in marine environments is of particular interest to oceanographers because of its effect on primary productivity. The high abundance of viruses in the ocean and their small size suggest that they might serve as nucleation centers for iron adsorption and precipitation in the ocean. Hence, we performed laboratory experiments to quantify the adsorption and precipitation of iron by a marine bacteriophage (PWH3a-P1). Acid–base titrations and zeta potential measurements were performed to determine if the virus interacted with protons, and if so, to determine the type, concentration, and reactivity of functional groups present on the viruses. Iron precipitation experiments were conducted to investigate interactions between iron and the viruses. The titrations and zeta potential measurements were well described by a model considering two types of reactive sites on the viruses, with log K values of −4.44 and −8.18, and a total site concentration of 3.64×10 −18 mol per virus. High-magnification observations of the viruses in the presence of iron by whole-mount transmission electron microscopy showed evidence of both adsorption and mineral nucleation. The experimental results clearly demonstrate the potential of marine bacteriophage to serve as nuclei for iron adsorption and precipitation, and the models developed from the data suggest that viruses might represent a significant reservoir of iron in seawater. However, these experiments utilized greatly simplified chemistry and a limited range of iron-to-virus concentration ratios relative to natural seawater, and so the results of this study do not prove that viruses affect the marine iron cycle, but rather serve to justify continued research into iron–virus interactions, in the laboratory and in the field.