Use of Poisons in Determination of Microbial Manganese Binding Rates in Seawater

A method was developed to determine whether microorganisms mediate the precipitation of manganese(II) in the marine environment. Radioactive ⁵⁴Mn(II) was used as a tracer to measure the precipitation (binding and oxidation) of Mn(II) i.e., the ⁵⁴Mn(II) trapped on 0.2-μm membrane filters] in the presence and absence of biological poisons. A variety of antibiotics, fixatives, and metabolic inhibitors were tested in laboratory control experiments to select poisons that did not interfere in the chemistry of manganese. The poisons were deemed suitable if (i) they did not complex Mn(II) more strongly than the ion-exchange resin Chelex 100, (ii) they did not interfere in the adsorption of ⁵⁴Mn(II) onto synthetic δMnO₂ (manganate), (iii) they did not cause desorption of ⁵⁴Mn(II) which had been preadsorbed onto synthetic manganate, and (iv) they did not solubilize synthetic ⁵⁴manganate. In addition, several known chelators, reducing agents, and buffers normally added to microbiological growth media or used in biochemical assays were tested. Most additions interfered to some extent with manganese chemistry. However, at least one inhibitor, sodium azide, or a mixture of sodium azide, penicillin, and tetracycline was shown to be appropriate for use in field studies of ⁵⁴Mn(II) binding. Formaldehyde could also be used in short incubations (1 to 3 h) but was not suitable for longer time course studies. The method was applied to studies of Mn(II) precipitation in Saanich Inlet, British Columbia, Canada. Bacteria were shown to significantly enhance the rate of Mn(II) removal from solution in the manganese-rich particulate layer which occurs just above the oxygen-hydrogen sulfide interface in the water column.