title: Sorption versus biomineralization of Pb(II) within Burkholderia cepacia biofilms.
abstract: X-ray spectroscopy measurements have been combined with macroscopic uptake data and transmission electron microscopy (TEM) results to show that Pb(II) uptake by Burkholderia cepacia is due to simultaneous sorption and biomineralization processes. X-ray microprobe mapping of B. cepacia biofilms formed on alpha-Al2O3 surfaces shows that Pb(II) is distributed heterogeneously throughout the biofilms because of the formation of Pb "hot spots". EXAFS data and TEM observations show that the enhanced Pb accumulation is due to the formation of nanoscale crystals of pyromorphite (Pb5(PO4)3(OH)) adjacent to the outer-membrane of a fraction of the total population of B. cepacia cells. In contrast, B. cepacia cell suspensions or biofilms that were heat-killed or pretreated with X-rays do not form pyromorphite, which suggests that metabolic activity is required. Precipitation of pyromorphite occurs over several orders of magnitude in [H-] and [Pb] and accounts for approximately 90% of the total Pb uptake below pH 4.5 but only 45-60% at near-neutral pH because of the formation of additional Pb(II) adsorption complexes. Structural fits of Pb L(III) EXAFS data collected for heat-treated cells at near-neutral pH suggest that Pb(II) forms inner-sphere adsorption complexes with carboxyl functional groups in the biofilms.
authors.affiliation: Surface & Aqueous Geochemistry Group, Department of Geological & Environmental Sciences, Stanford University, Stanford, California 94035-2115, USA. atempleton@ucsd.edu
authors.forename: Alexis S
authors.initials: AS
authors.lastname: Templeton
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Trainor
authors.forename: Alfred M
authors.initials: AM
authors.lastname: Spormann
authors.forename: Mathew
authors.initials: M
authors.lastname: Newville
authors.forename: Steven R
authors.initials: SR
authors.lastname: Sutton
authors.forename: Alice
authors.initials: A
authors.lastname: Dohnalkova
authors.forename: Yuri
authors.initials: Y
authors.lastname: Gorby
authors.forename: Gordon E
authors.initials: GE
authors.lastname: Brown
mesh_terms: D000327:Adsorption; D018441:Biofilms; D016956:Burkholderia cepacia / Q000737:chemistry* / Q000502:physiology; D011232:Chemical Precipitation; D007854:Lead / Q000493:pharmacokinetics*; D008854:Microscopy, Electron; D008903:Minerals / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D013057:Spectrum Analysis
chemical_list: D008903:Minerals; D010710:Phosphates; C471364:pyromorphite; D007854:Lead