title: Extracellular polymeric substances from Bacillus subtilis associated with minerals modify the extent and rate of heavy metal sorption.
abstract: Extracellular polymeric substances (EPS) are an important source of organic matter in soil. Once released by microorganisms, a portion may be sorbed to mineral surfaces, thereby altering the mineral̀s ability to immobilize heavy metals. EPS from Bacillus subtilis were reacted with Ca-saturated bentonite and ferrihydrite in 0.01 M KCl at pH 5.0 to follow the preferential uptake of EPS-C, -N, and -P. The sorption kinetics of Pb(2+), Cu(2+), and Zn(2+) to the resulting EPS-mineral composites was studied in single and binary metal batch experiments ([metal](total) = 50 μM, pH 5.0). Bentonite sorbed much more EPS-C (18.5 mg g(-1)) than ferrihydrite (7.9 mg g(-1)). During sorption, EPS were chemically and size fractionated with bentonite favoring the uptake of low-molecular weight components and EPS-N, and ferrihydrite selectively retaining high-molecular weight and P-rich components. Surface area and pore size measurements by N(2) gas adsorption at 77 K indicated that EPS altered the structure of mineral-EPS associations by inducing partial disaggregation of bentonite and aggregation of ferrihydrite. Whereas mineral-bound EPS increased the extent and rate of Pb(2+), Cu(2+), and Zn(2+) sorption for bentonite, either no effect or a decrease in metal uptake was observed for ferrihydrite. The extent of sorption always followed the order Pb(2+) > Cu(2+) > Zn(2+), which also prevailed in binary Pb(2+)/Cu(2+) systems. In consequence, sorption of EPS to different minerals may have contrasting consequences for the immobilization of heavy metals in natural environments by inducing mineral-specific alterations of the pore size distribution and, thus, of available sorption sites.
authors.affiliation: Institut für Bodenkunde, Leibniz Universität Hannover, Hannover, Germany. mikutta@ifbk.uni-hannover.de
authors.forename: Robert
authors.initials: R
authors.lastname: Mikutta
authors.forename: Anja
authors.initials: A
authors.lastname: Baumgärtner
authors.forename: Axel
authors.initials: A
authors.lastname: Schippers
authors.forename: Ludwig
authors.initials: L
authors.lastname: Haumaier
authors.forename: Georg
authors.initials: G
authors.lastname: Guggenberger
mesh_terms: D000327:Adsorption; D001412:Bacillus subtilis / Q000737:chemistry*; D001546:Bentonite / Q000737:chemistry; D001673:Biodegradation, Environmental; D001704:Biopolymers / Q000302:isolation & purification / Q000378:metabolism*; D005591:Chemical Fractionation; D004058:Diffusion; D004586:Electrophoresis; D005110:Extracellular Space / Q000737:chemistry*; D005290:Ferric Compounds / Q000737:chemistry; D007700:Kinetics; D019216:Metals, Heavy / Q000302:isolation & purification*; D008903:Minerals / Q000737:chemistry*; D008956:Models, Chemical; D010316:Particle Size; D016062:Porosity; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D013997:Time Factors
chemical_list: D001704:Biopolymers; D005290:Ferric Compounds; D019216:Metals, Heavy; D008903:Minerals; D001546:Bentonite; C092844:ferric oxyhydroxide