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

Abstract

Pseudomonas putida strain MnB1, a biofilm-forming bacterial culture, was used as a model for the study of bacterial Mn oxidation in freshwater and soil environments. The oxidation of aqueous Mn ؉2 [Mn ؉2(aq) ] by P. putida was characterized by spatially and temporally resolving the oxidation state of Mn in the presence of a bacterial biofilm, using scanning transmission X-ray microscopy (STXM) combined with near-edge X-ray absorption fine structure (NEXAFS) spectroscopy at the Mn L 2,3 absorption edges. Subsamples were collected from growth flasks containing 0.1 and 1 mM total Mn at 16, 24, 36, and 48 h after inoculation. Immediately after collection, the unprocessed hydrated subsamples were imaged at a 40-nm resolution. Manganese NEX-AFS spectra were extracted from X-ray energy sequences of STXM images (stacks) and fit with linear combinations of well-characterized reference spectra to obtain quantitative relative abundances of Mn(II), Mn(III), and Mn(IV). Careful consideration was given to uncertainty in the normalization of the reference spectra, choice of reference compounds, and chemical changes due to radiation damage. The STXM results confirm that Mn ؉2 (aq) was removed from solution by P. putida and was concentrated as Mn(III) and Mn(IV) immediately adjacent to the bacterial cells. The Mn precipitates were completely enveloped by bacterial biofilm material. The distribution of Mn oxidation states was spatially heterogeneous within and between the clusters of bacterial cells. Scanning transmission X-ray microscopy is a promising tool for advancing the study of hydrated interfaces between minerals and bacteria, particularly in cases where the structure of bacterial biofilms needs to be maintained.The chemistry of many aqueous environments is dictated by reactions that occur at the interface between the aqueous solution phase and the solid mineral and organic phases (43). It is at this interface that microorganisms also accumulate (4, 14). Microorganisms are known to form layered communities (biofilms) characterized by production of extracellular polymers, in which the physical and chemical conditions may differ greatly from those of the bulk solution. Within the biofilm setting, microorganisms carry out dissolution and precipitation of minerals, exerting direct influence on the cycling of trace and contaminant metals alike (18,51).In particular, the precipitation of manganese (Mn) in soils, sediments, and water columns is primarily driven by microbial activity (11,18,33). Although conditions are thermodynamically favorable for the oxidation of aqueous Mn ϩ2 [Mn ϩ2 (aq) ] in the presence of dissolved oxygen, the homogeneous (reaction involving only solution-phase reactants) kinetics of oxidation are slow (32). Rates of Mn oxidation observed in natural waters are often too high to be attributed to homogeneous or surface-mediated reactions (32). Microbial processes are thought to control the precipitation and dissolution of Mn oxides in many natural systems, and Mn-oxidizing microorganisms have been isolated ...

Mechanisms of nickel sorption by a bacteriogenic birnessite

“…Pseudomonas putida cultures were propagated in 250 mL Erlenmeyer flasks containing 125 mL of Leptothrix medium inoculated with a culture grown overnight to achieve a thousandfold dilution factor. Cultures were incubated on a rotary shaker (150 RPM, 27 °C) for 5.7 ± 0.1 days, allowing for 90 -100 % of the added Mn(II) to be removed from solution by oxidation and precipitation as birnessite and/or sorption (Toner et al, 2005a). At the time of harvesting, the biomass-birnessite suspension had a pH value of 6.0 ± 0.1.…”

“…Solutions were prepared using Milli-Q (MQ) water with a resistivity of 18.2 MΩ-cm. Birnessite was produced using a Pseudomonas putida GB-1 culture (Villalobos et al, 2003;Toner et al, 2005a et al, 2007). Pseudomonas putida cultures were propagated in 250 mL Erlenmeyer flasks containing 125 mL of Leptothrix medium inoculated with a culture grown overnight to achieve a thousandfold dilution factor.…”

“…1, the metal cations to the left of the square brackets are hydrated interlayer species balancing the negative structural charge have been measured by Villalobos et al (2003) and Duckworth and Sposito (2007). Biogenic birnessite minerals such as this are typically found enmeshed in an organic matrix of bacterial cells and extracellular polymeric substances (Tebo et al, 2004;Tebo et al, 2005;Toner et al, 2005a), thus forming heterogeneous biomass-mineral assemblages that contain a variety of reactive organic functional groups, such as -COOH, -CHOH, -PO 4 H 3 , -SH, and -NH 2 (Fein et al, 2001;Warren and Haack, 2001;Toner et al, 2005b;Sposito, 2008), as well as mineral sorption sites.…”

Preservation of iron(II) by carbon-rich matrices in a hydrothermal plume

“…We rule out dissolved Fe because the concentration would have to approach 0.1 mM to be detected by STXM-NEXAFS (ref. 13). We can also exclude uniformly distributed nanoparticulate minerals on the basis of Fe 2p NEXAFS spectra because the Fe(ii) spectra (Fig.…”

Speciation and Quantitative Mapping of Metal Species in Microbial Biofilms Using Scanning Transmission X-ray Microscopy

“…The more oxidized species were found to be located outside the cell membrane. STXM at the Mn 2p edge was used to observe planktonic P. putida bacteria transform Mn 2+ to Mn 3+ and Mn 4+ as a function of time (23). The distribution of the Mn oxidation states in the cell and EPS was quantified from selected regions with a linear regression fit to reference spectra normalized to the computed atomic absorption value in the Mn 2p postedge.…”