Surface Display of Metal Fixation Motifs of Bacterial P1-Type ATPases Specifically Promotes Biosorption of Pb2+ by Saccharomyces cerevisiae

Biosorption of metal ions may take place by different passive metal-sequestering processes such as ion exchange, complexation, physical entrapment, and inorganic microprecipitation or by a combination of these. To improve the biosorption capacity of the potential yeast biosorbent, short metal-binding NP peptides (harboring the CXXEE metal fixation motif of the bacterial Pb2+-transporting P1-type ATPases) were efficiently displayed and covalently anchored to the cell wall of Saccharomyces cerevisiae. These were fusions to the carboxyl-terminal part of the sexual adhesion glycoprotein alpha-agglutinin (AG alpha 1Cp). Compared to yeast cells displaying the anchoring domain only, those having a surface display of NP peptides multiplied their Pb2+ biosorption capacity from solutions containing a 75 to 300 mu M concentration of the metal ion up to 5-fold. The S-type Pb2+ biosorption isotherms, plus the presence of electron-dense deposits ( with an average size of 80 by 240 nm, observed by transmission electron microscopy) strongly suggested that the improved biosorption potential of NP-displaying cells is due to the onset of microprecipitation of Pb species on the modified cell wall. The power of an improved capacity for Pb biosorption was also retained by the isolated cell walls containing NP peptides. Their Pb2+ biosorption property was insensitive to the presence of a 3-fold molar excess of either Cd2+ or Zn2+. These results suggest that the biosorption mechanism can be specifically upgraded with microprecipitation by the engineering of the biosorbent with an eligible metal-binding peptide.