Surface Complexation Modeling of Terbium Biosorption onto E. Coli Bacterial Surfaces with Lanthanide Binding Tags

Lanthanide binding tags (LBTs) have been engineered onto native Escherichia coli (E. coli) bacterial surfaces to enhance extraction and recovery of rare earth elements (REEs). Three strains of E. coli were studied: (1) the native E. coli surface, (2) a mutant E. coli surface with hindered, non-binding lanthanide binding tags, and (3) an LBT E. coli surface with fully functioning lanthanide binding tags. A three discrete site, constant capacitance surface complexation modeling approach was taken in studying these strains with an ultimate goal of comparing site type affinities to the model rare earth, Terbium. Our results show a possible increase in native carboxyl functional groups when the LBTs are overexpressed on the cell surface. LBTs are confirmed to have a higher stability constant with Terbium than that of the native functional groups. Incorporation of LBTs into the E. coli cell wall poses two major benefits: (1) the presence of a high-affinity, low-capacity LBT site for selective Terbium binding at low metal loading regions, and (2) a lower-affinity carboxyl site that increases the sorption capacity of the native bacterial surface during sorption at higher metal loading regions.