SummaryMeasurements have been made of calcium and magnesium uptake to barley seedlings (Hordeum vulgare) growing on nutrient solutions. Uptake to the shoot increased with solution concentration and showed a preference for magnesium, largely due to the action of transpiration. Though uptake of both ions was increased by higher transpiration, magnesium was more affected than was calcium. In the root, calcium was taken up preferentially to magnesium, and the levels were not affected by transpiration rate.Uptake of calcium and magnesium was little affected by the concentration of sodium and potassium, and appears to be a separate process. The main difference between uptake of monovalent and divalent cations was that uptake of monovalent ions was largely independent of concentration, but uptake of divalent cations was proportional to it.
The oxidation of ferrous ions, in acid solution, by resting suspensions of Thiobacillus ferrooxidans produced sediments consisting of crystalline jarosites, amorphous ferric hydroxysulfates, or both. These products differed conspicuously in chemical composition and infrared spectra from precipitates formed by abiotic oxidation under similar conditions. The amorphous sediments, produced by bacterial oxidation, exhibited a distinctive fibroporous microstructure when examined by scanning electron microscopy. Infrared spectra indicated outersphere coordination of Fe(III) by sulfate ions, as well as inner-sphere coordination by water molecules and bridging hydroxo groups. In the presence of excess sulfate and appropriate monovalent cations, jarosites, instead of amorphous ferric hydroxysulfates, precipitated from bacterially oxidized iron solutions. It is proposed that the jarositic precipitates result from the conversion of outer-sphere (Td) sulfate, present in a soluble polymeric Fe(III) complex, to inner-sphere (C30) bridging sulfate. The amorphous precipitates result from the further polymerization of hydroxo-linked iron octahedra and charge stabilized aggregation of the resulting iron complexes in solution. This view was supported by observations that bacterially oxidized iron solutions gave rise to either amorphous or jarositic sediments in response to ionic environments imposed after oxidation had been completed and the bacteria had been removed by filtration.
The anionic requirement for the oxidation of ferrous ions by suspensions of Thiobacillus ferrooxidans was satisfied by selenate as well as sulphate. Selenate was toxic to the organism and suppressed growth in ferrous iron media, even in the presence of high concentrations of sulphate. After treatment with dilute hydrochloric acid at o "C, T. ferrooxidans, which specifically required S042-or Se042-for iron oxidation, showed no activity in response to 12 other anions tested. However, after the introduction of or Se042-, addition of anions such as Te0,2-, WO2-, AS043-or Po43-further enhanced the rate of iron oxidation. Under these conditions, C1-, B40,2-and C103-had no significant effect at low concentration, whereas Br-, NO3-and Mo02-were inhibitory. These observations distinguish between a specific and a non-specific anionic requirement for the oxidation of ferrous ions by T. ferrooxidans. The specific requirement is satisfied only through the uptake of S042-or SeOd2-by the bacteria. The non-specific requirement is satisfied by any one of several anions, including SO,2-and Se0,2-, which are presumed to act as ligands for iron in solution.
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