HR: 08:45h
AN: B11A-03    [PDF]
TI: Adhesion of Bacterial EPS to Goethite and Silica Surfaces
AU: * Chorover, J
EM: chorover@cals.arizona.edu
AF: Department of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ 85721 United States
AU: Omoike, A
EM: ansomo@ag.arizona.edu
AF: Department of Soil, Water and Environmental Science, University of Arizona, Tucson, AZ 85721 United States
AB: Bacterial adhesion to mineral surfaces is mediated by cell surface macromolecules including lipopolysaccharides, lipoteichoic acids, surface proteins and extracellular polymeric substances (EPS). EPS, a heterogeneous mixture of polysaccharides, proteins and nucleic acids that occur in both cell-bound (capsular) and free form, are thought to mediate cell adhesion through modification of cell surface chemistry and formation of conditioning films, but molecular-scale interactions are not well known. We isolated EPS from the exponential and stationary growth phases of Bacillus subtilis, a common soil bacterium, and characterized them using spectroscopy (XPS, FTIR, NMR) and high pressure size exclusion chromatography (HPSEC). Attenuated total reflectance (ATR)- FTIR was employed to probe EPS adsorption from aqueous solution to goethite and amorphous silica colloids that were coated onto a Ge internal reflectance element. Relative intensity of IR bands characteristic of protein, polysaccharides and nucleic acids were dependent on growth phase and type of EPS (free or cell-bound). Proton complexation at acidic functional groups resulted in protein conformational changes; alpha-helical conformation was observed at pH $<$ 4 and random coil (unordered) conformation at pH $>$ 6. The apparent molecular mass estimated by HPSEC ranged from 0.42-132 kDa and peak elution times exhibited significant dependence on aqueous chemistry reflecting changes in conformation. EPS exhibited higher affinity for goethite than for silica but sorption to both solids resulted in molecular changes that were detectable by FTIR. We observed an increase in amide II band intensity and an amide I band shift to higher wavenumbers, suggesting changes in EPS secondary structure of proteins upon adsorption. Silica-sorbed EPS exhibited weak polysaccharide bands whereas sorption to goethite showed polysaccharide fractionation. Distinct spectral features indicative of the formation of P-O-Fe bonds were observed in all the goethite-sorbed EPS spectra, suggesting that phosphates from nucleic acid constituents of EPS play a prominent role in the adsorption process.
DE: 1045 Low-temperature geochemistry
DE: 1055 Organic geochemistry
DE: 1094 Instruments and techniques
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting