Production of biogenic Mn oxides by leptothrix discophora SS-1 in a chemically defined growth medium and evaluation of their Pb adsorption characteristics

Abstract

Biogenic Mn oxides were produced by the bacterium Leptothrix discophora SS-1 (= ATCC 3182) in a chemically defined mineral salts medium, and the Pb binding and specific surface area of these oxides were characterized. Growth of SS-1 in the defined medium with pyruvate as a carbon and energy source required the addition of vitamin B12. Complete oxidation of Mn(II) within 60 h required the addition of >/=0.1 &mgr;M FeSO4. Pb adsorption isotherms were determined for the biogenic Mn oxides (and associated cells with their extracellular polymer) and compared to the Pb adsorption isotherms of cells and exopolymer alone, as well as to abiotic Mn oxides. The Pb adsorption to cells and exopolymer with biogenic Mn oxides (0.8 mmol of Mn per g) at pH 6.0 and 25 degreesC was 2 orders of magnitude greater than the Pb adsorption to cells and exopolymer alone (on a dry weight basis). The Pb adsorption to the biogenic Mn oxide was two to five times greater than the Pb adsorption to a chemically precipitated abiotic Mn oxide and several orders of magnitude greater than the Pb adsorption to two commercially available crystalline MnO2 minerals. The N2 Brunauer-Emmet-Teller specific surface areas of the biogenic Mn oxide and fresh Mn oxide precipitate (224 and 58 m2/g, respectively) were significantly greater than those of the commercial Mn oxide minerals (0.048 and 4. 7 m2/g). The Pb adsorption capacity of the biogenic Mn oxide also exceeded that of a chemically precipitated colloidal hydrous Fe oxide under similar solution conditions. These results show that amorphous biogenic Mn oxides similar to those produced by SS-1 may play a significant role in the control of trace metal phase distribution in aquatic systems.

FIG. 1

Fe requirement for Mn oxidation by L. discophora SS-1 in MMS medium (Fe and Mn were added at the time of inoculation).

FIG. 2

Pb adsorption isotherms for L. discophora SS-1 cells. (A) Without Mn. (B) With biogenic Mn oxide (0.8 mmol/g). The temperature was 25°C, the pH was 6.0, and the concentration of total suspended solids was 63 mg/liter.

FIG. 3

Pb adsorption to biogenic Mn oxide and fresh abiotic δMnO₂ precipitates. Symbols: •, biogenic replicate 1; ■, biogenic replicate 2; ▴, biogenic replicate 3; ⧫, biogenic replicate 4; ○, abiotic replicate 1; □, abiotic replicate 2; ▵, abiotic replicate 3.

FIG. 4

Comparison of Pb adsorption by biogenic Mn oxide, by abiotic δMnO₂ precipitates, by commercial Mn oxide minerals, and by colloidal Fe oxide (log scale).