Manganite reduction by Shewanella putrefaciens MR-4

Abstract

Previous studies have documented dissimilatory growth of bacteria on solid Mn 4ϩ oxide, but Mn 3ϩ oxides have not been previously studied; here we have demonstrated for the first time the bacterial reduction of manganite. Strain MR-4 of Shewanella putrefaciens was able to grow on and rapidly reduce insoluble needle-shaped crystals of synthetic manganite (MnOOH), converting them to soluble Mn 2ϩ in the process. The rate of Mn 3ϩ reduction was optimal at pH of 7.0 and 26 ЊC consistent with an enzymatic reaction. In addition the rates of reduction were in proportion to the amount of manganite added, but nearly independent of the cell concentration present (e.g., cell number had only a small effect on the rate of Mn 3ϩ reduction at early stages of growth) suggesting that surface properties were dictating the rates of metal reduction. This thesis was supported by major differences in reduction rates when Mn oxides of different surface areas were studied. Removal of the carbon source (formate or lactate) or addition of metabolic inhibitors reduced the rate of metal reduction. No Mn 3ϩ reduction was observed when the samples were oxygenated, nor when the cells were separated from the Mn 3ϩ oxide by a dialysis membrane. Environmental scanning electron microscopy (ESEM) images showed close contact of the cells with the needle-shaped crystals during early stages of reduction. In later stages, the closely associated cells were coated with a layer of extracellular polymeric material that obscured the cells when viewed by ESEM. When manganite crystals were dried and gold coated, and viewed by standard scanning electron microscopy (SEM), abundant bacteria could be seen on the surface of the metal oxide in a thin biofilm-like layer. The layer of extracellular polymer is a new finding, and neither the composition, function, nor importance in the manganese reduction process have been elucidated.

Spatially Resolved Characterization of Biogenic Manganese Oxide Production within a Bacterial Biofilm

“…The hausmannite (Mn 3 O 4 ) and bixbyite (Mn 2 O 3 ) were purchased from Sigma Corp. The manganite, acid birnessite, triclinic Na-birnessite, c-disordered H-birnessite, and ␦-Mn(IV)O 2 were synthesized in the laboratory (28,31,50). The reference and test materials were characterized with powder XRD, N 2 Brunauer-Emmett-Teller specific surface area determination, and chemical titration to determine the average Mn oxidation number.…”

Alteration of iron‐rich lacustrine sediments by dissimilatory iron‐reducing bacteria

“…Instead, MnHPO 4 was supersaturated throughout the experiment, although it should be noted that shifting the pH of the system above pH 7 would provide thermodynamically favourable conditions for the formation of vivianite. The production of EPS in the presence of LMS but not Gt is consistent with previous observations that the production of EPS by S. putrefaciens depends on the composition of the electron acceptor substrate (Little et al ., 1997;Larsen et al ., 1998) and may be related to the presence of Mn oxyhydroxides. Amorphous Si remained undersaturated throughout the incubations, suggesting that diatoms present in the sediment could dissolve during Fe reduction.…”

“…Cell assemblages are smaller and are more discretely distributed on the Gt surface. The production of EPS in the presence of LMS but not Gt is consistent with previous observations that the production of EPS by S. putrefaciens depends on the composition of the electron acceptor substrate (Little et al ., 1997;Larsen et al ., 1998) and may be related to the presence of Mn oxyhydroxides. The extensive EPS-cell assemblages observed on LMS may impede Fe reduction by forming a barrier between the mineral/bacterial surfaces and the bulk solution.…”

Catalytic reduction of NACs by nano Fe3O4/quinone composites in the presence of a novel marine exoelectrogenic bacterium under hypersaline conditions

“…Sequentially, the marine indigenous bacteria were isolated using a dilution plate method at 30 C. The exoelectrogenic ability of the obtained bacterium was tested on the basis of the method described by Larsen. 22 Briey, a dialysis membrane (100-500 D) was employed to separate 1 mL strain cells (OD 600 ¼ 1.141) from 0.1 mM NC (>500 D), the bacterium with the highest NC reduction rate without direct contact was selected for further study. In this study, the strain CNZ-1 was thus selected and identied by scanning electron microscope (SEM) and 16S rRNA gene sequencing analysis.…”