title: STXM and NanoSIMS investigations on EPS fractions before and after adsorption to goethite.
abstract: Extracellular polymeric substances (EPS) are expected to be an important source for the formation of mineral-organic associations in soil. Because such formations affect the composition of mobile and immobile organic matter as well as the reactivity of minerals, we investigated the composition of EPS before and after adsorption to goethite. Raman measurements on EPS extracted from Bacillus subtilis distinguished four fractions rich in proteins, polysaccharides, lipids, or lipids and proteins. Scanning transmission X-ray microscopy identified three different EPS-fractions that varied in their composition in proteins, nonaromatic proteins, and polysaccharides. Reaction of EPS with goethite led to a preferential adsorption of lipids and proteins. The organic coverage was heterogeneous, consisting of ~100 × 200 nm large patches of either lipid-rich or protein-rich material. Nanoscale secondary ion mass spectrometry showed a strong S enrichment in aggregates of ~400 nm in the goethite adsorbed EPS. From our simplified model system, we learned that only a small portion (<10%) of EPS was immobilized via adsorption to goethite. This fraction formed a coating of subμm spaced protein-rich and lipid-rich domains, i.e., of two materials which will strongly differ in their reactive sites. This will finally affect further adsorption, the particle mobility and eventually also colloidal stability.
authors: Institut für Geowissenschaften, Friedrich-Schiller-Universität Jena, Germany.
authors: Xinran
authors: X
authors: Liu
authors: Karin
authors: K
authors: Eusterhues
authors: Jürgen
authors: J
authors: Thieme
authors: Valerian
authors: V
authors: Ciobota
authors: Carmen
authors: C
authors: Höschen
authors: Carsten W
authors: CW
authors: Mueller
authors: Kirsten
authors: K
authors: Küsel
authors: Ingrid
authors: I
authors: Kögel-Knabner
authors: Petra
authors: P
authors: Rösch
authors: Jürgen
authors: J
authors: Popp
authors: Kai U
authors: KU
authors: Totsche
mesh_terms: D000327:Adsorption; D001704:Biopolymers / Q000737:chemistry*; D002247:Carbon Isotopes; D005110:Extracellular Space / Q000737:chemistry*; D058085:Iron Compounds / Q000737:chemistry*; D008853:Microscopy / Q000379:methods*; D015591:Microspectrophotometry; D008903:Minerals / Q000737:chemistry*; D053758:Nanoparticles / Q000737:chemistry*; D018629:Spectrometry, Mass, Secondary Ion / Q000379:methods*; D017550:Spectroscopy, Fourier Transform Infrared; D013059:Spectrum Analysis, Raman
chemical_list: D001704:Biopolymers; D002247:Carbon Isotopes; D058085:Iron Compounds; D008903:Minerals; C094886:goethite