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

Abstract

A scanning transmission X-ray microscope illuminated with synchrotron light was used to investigate the speciation and spatial distributions of metals in a microbial biofilm cultivated from river water. Metal 2p absorption edge signals were used to provide metal speciation (through shapes of the absorption spectra) and quantitative spatial distributions of the metal species. This paper presents sample data and describes methods for extracting quantitative maps of metal species from image sequences recorded in the region of the metal 2p edges. Comparisons were made with biochemical characterization of the same region using images recorded at the C 1s and O 1s edges. The method is applied to detailed quantitative analysis of ferrous and ferric iron in a river biofilm, in concert with mapping Ni-(II) and Mn(II) species in the same region. The distributions of the metal species are discussed in the context of the biofilm structure. These results demonstrate that soft X-ray STXM measurements at the metal 2p absorption edges can be used to speciate metals and to provide quantitative spatial distribution maps for metal species in environmental samples with 50 nm spatial resolution.

Iron oxyhydroxide mineralization on microbial extracellular polysaccharides

“…Synchrotron-based scanning transmission X-ray spectromicroscopy (STXM) enables the study of the minerals and organic functional group chemistry of hydrated samples with high spatial and spectral resolutions (<40 nm and <0.1 eV, respectively). STXM has proven to be a useful tool for studying both organics and metals in biofilms and biominerals, as demonstrated by work on Mn-oxidizing bacteria (Pecher et al, 2003;Toner et al, 2005), microbial calcification (Benzerara et al, 2004(Benzerara et al, , 2006, and river biofilms (Lawrence et al, 2003;Dynes et al, 2006). We performed synthesis experiments to simulate the postulated mineralization pathway, and used STXM-based carbon and iron near edge Xray absorption fine structure (NEXAFS) spectroscopy to observe the progression of polymer-iron interactions during the course of mineral formation.…”

Quantitative Evaluation of Radiation Damage to Polyethylene Terephthalate by Soft X-rays and High-energy Electrons

“…[4][5][6][7][8][9][10][11] Better understanding of damage mechanisms and more accurate determinations of damage rates for polymers are not only important to the areas mentioned above, but also to the field of soft X-ray spectromicroscopy, which is increasingly being applied to organic materials [12][13][14][15] and biological samples. 14,16,17 A complete bibliography of soft X-ray spectromicroscopy has recently been published in association with a recent review of polymer applications 15 and updates can be obtained from http://unicorn. mcmaster.ca/xrm-biblio/xrm_bib.html.…”

Microscopic and Spectroscopic Analyses of Chlorhexidine Tolerance in Delftia acidovorans Biofilms

“…Quantitative component maps of the major biomacromolecules (proteins, lipids, and polysaccharides) as well as CO 3 2Ϫ , K ϩ , and CHX, were derived by fitting the image sequences at each pixel to the spectra of the reference compounds that had been placed on an absolute linear absorbance scale using the singular value decomposition procedure (38). Absolute linear absorbance is the optical density (OD) per unit path length of a pure material of a defined density, where the absorbance (A), also called OD, is given by the equation A ϭ OD ϭ Ϫln(I/Io), where I is the transmitted intensity and Io is the incident intensity, and it is established by adjusting the intensity scale of the reference spectrum to that of the computed elemental response outside the structured near-edge region (41). The lower and upper limits of the gray scale indicated in the component maps are a measure of the component thickness in nm.…”

“…The lower and upper limits of the gray scale indicated in the component maps are a measure of the component thickness in nm. The reliability and methodology used to quantitatively map the major biomacromolecules in biofilm cells have been described in detail elsewhere (19,23,41). The reference compounds used were protein (human serum albumin), lipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine), polysaccharide (xanthan gum), carbonate (calcite), K (K 2 CO 3 with CO 3 derived from Ca carbonate subtracted) (20,22), and chlorhexidine dihydrochloride (CHX).…”