Production of Manganese Oxide Nanoparticles by Shewanella Species - PubMed (original) (raw)

Production of Manganese Oxide Nanoparticles by Shewanella Species

Mitchell H Wright et al. Appl Environ Microbiol. 2016.

Abstract

Several species of the bacterial genus Shewanella are well-known dissimilatory reducers of manganese under anaerobic conditions. In fact, Shewanella oneidensis is one of the most well studied of all metal-reducing bacteria. In the current study, a number of Shewanella strains were tested for manganese-oxidizing capacity under aerobic conditions. All were able to oxidize Mn(II) and to produce solid dark brown manganese oxides. Shewanella loihica strain PV-4 was the strongest oxidizer, producing oxides at a rate of 20.3 mg/liter/day and oxidizing Mn(II) concentrations of up to 9 mM. In contrast, S. oneidensis MR-1 was the weakest oxidizer tested, producing oxides at 4.4 mg/liter/day and oxidizing up to 4 mM Mn(II). Analysis of products from the strongest oxidizers, i.e., S loihica PV-4 and Shewanella putrefaciens CN-32, revealed finely grained, nanosize, poorly crystalline oxide particles with identical Mn oxidation states of 3.86. The biogenic manganese oxide products could be subsequently reduced within 2 days by all of the Shewanella strains when culture conditions were made anoxic and an appropriate nutrient (lactate) was added. While Shewanella species were detected previously as part of manganese-oxidizing consortia in natural environments, the current study has clearly shown manganese-reducing Shewanella species bacteria that are able to oxidize manganese in aerobic cultures.

Importance: Members of the genus Shewanella are well known as dissimilatory manganese-reducing bacteria. This study shows that a number of species from Shewanella are also capable of manganese oxidation under aerobic conditions. Characterization of the products of the two most efficient oxidizers, S. loihica and S. putrefaciens, revealed finely grained, nanosize oxide particles. With a change in culture conditions, the manganese oxide products could be subsequently reduced by the same bacteria. The ability of Shewanella species both to oxidize and to reduce manganese indicates that the genus plays a significant role in the geochemical cycling of manganese. Due to the high affinity of manganese oxides for binding other metals, these bacteria may also contribute to the immobilization and release of other metals in the environment.

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Figures

FIG 1

FIG 1

Optimal concentrations of Mn(II) oxidized by the Shewanella species S. loihica, S. putrefaciens, S. oneidensis, and S. denitrificans. No manganese oxides were formed in sterile controls or in poisoned controls with any of the Shewanella species.

FIG 2

FIG 2

Extent of manganese oxidation (▲) and increases in cell numbers (cells per milliliter) (■) over time for Shewanella putrefaciens CN-32 (a) and Shewanella loihica PV-4 (b). Cultures were grown with 3 mM Mn(II). The extent of manganese oxidation in poisoned controls is also shown (●).

FIG 3

FIG 3

Manganese oxide formation (▲) and cell number (cells per milliliter) (■) variations over time for Shewanella putrefaciens CN-32 (a) and Shewanella loihica PV-4 (b), initially under aerobic conditions. After 10 days of incubation, conditions were changed to anaerobic (N2 gas) with the addition of 15 mM lactate (arrows).

FIG 4

FIG 4

FTIR spectroscopy of manganese oxides formed by Shewanella putrefaciens CN-32 (a), manganese oxides formed by Shewanella loihica PV-4 (b), and analytical reagent-grade MnO2 (c).

FIG 5

FIG 5

Scanning electron microscopy of manganese oxides formed by Shewanella putrefaciens CN-32 (a), manganese oxides formed by Shewanella loihica PV-4 (b), and analytical reagent-grade MnO2 (c). Arrows indicate bacteria.

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This research was supported by an Australian Postgraduate Award for Mitchell H. Wright.

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