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Applied and Environmental Microbiology, March 2005, p. 1300-1310, Vol. 71, No. 3
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.3.1300-1310.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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

Brandy Toner,^1,* Sirine Fakra,^2, Mario Villalobos,³ Tony Warwick,² and Garrison Sposito¹

Department of Environmental Science, Policy and Management, Division of Ecosystem Sciences, University of California,¹ Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California,² Grupo de Biogeoquímica Ambiental, LAFQA, Instituto de Geografía, Ciudad Universitaria, UNAM, Mexico City, Mexico³

Received 4 June 2004/ Accepted 9 October 2004

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 NEXAFS 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.

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* Corresponding author. Present address: Geomicrobiology Group, Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02536. Phone: (510) 427-0001. E-mail: toner{at}cal.berkeley.edu.

B.T. and S.F. contributed equally to the present research.

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Applied and Environmental Microbiology, March 2005, p. 1300-1310, Vol. 71, No. 3
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.3.1300-1310.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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