Surface complexation model of rare earth element adsorption onto bacterial surfaces with lanthanide binding tags. (January 2020)

• Record Type: Journal Article
• Authors: Chang, Elliot; Brewer, Aaron W.; Park, Dan M.; Jiao, Yongqin; Lammers, Laura N.
• Is Part Of: Applied geochemistry. Volume 112(2020)
• Publication Date: 2020-01
• Subjects: Surface complexation modeling -- Rare earth elements -- REE -- Biosorption -- Bioadsorption -- Surface complexation -- Lanthanide binding tag; Environmental geochemistry -- Periodicals; Water chemistry -- Periodicals; Geochemistry -- Social aspects -- Periodicals; Geochemistry -- Periodicals; 551.9
• DOI: 10.1016/j.apgeochem.2019.104478
• Languages: English
• ISSNs: 0883-2927

Abstract

Abstract: Lanthanide binding tags (LBTs) have been engineered onto the cell surface of E. coli to enhance biosorption and recovery of rare earth elements (REEs). The protonation behavior of the bacterial surfaces before and after LBT-display was compared by modeling acid-base titration data. A multiple discrete site, constant capacitance surface complexation model was constructed to examine rare earth (Tb) binding to cell surface functional groups, comparing wild type and LBT-engineered surfaces. Our acid-base titrations show similar pKa values between the two strains, suggesting induction of LBTs does not significantly alter cell surface protonation behavior. Tb sorption onto the wild type cell surface can be captured by a one-site carboxyl model. The LBT strain exhibited a higher metal loading that can be explained by the increase of sorption sites in the form of lanthanide binding tags. Furthermore, carboxyl site concentrations between wild type and LBT-induced cells were statistically indistinguishable. We thus attribute the engineered strains' increase in Tb adsorption capacity and affinity to the addition of lanthanide binding tags to the cell surface. The Tb stability constant with the LBT site is two orders of magnitude higher than that with the carboxyl functional group. As a result, at low metal loading <10 μM, the Tb binding to the cell surface of the LBT-strain is controlled by the presence of high-affinity, but lower capacity, LBT sites. At higher metal loadings >10 μM, a more abundant but low affinity functional group becomes the main source of adsorption that results in an overall higher sorption capacity. This work demonstrates how surface complexation modeling can be implemented for bacterial surfaces engineered with a known protein tag to optimize REE recovery from fluids with variable pH and metal loadings. Highlights: Bioengineered E. coli display increased sorption capacity and affinity for rare earths. Engineered LBT sites have higher affinity for rare earths than wild type surface sites. REE-cell surface binding mode depends on both pH and aqueous concentration.