Yeast Biosorption and Recycling of Metal Ions by Cell Surface Engineering

Abstract

Metal biosorption by microorganisms contributes to the removal of toxic heavy metal ions and collection of metal resources from waste streams. Cell surface biosorption enhanced by cell surface engineering is a unique and effective approach for the construction of a novel biosorbent. Through biosorption, adsorbed metal ions can be easily recovered without disintegration of cells, and the repeated use of cells as adsorbents for the biosorption and recuperation of metal ions becomes feasible. Thus, engineering of cell surfaces for enhanced biosorption of metal ions has the potential to be more suitable than genetic manipulations that promote intracellular accumulation. Metal-binding proteins and peptides were displayed on the yeast cell surface by an α-agglutinin-based display system, and cell surface-engineered yeasts showed enhanced biosorption of, and tolerance to, heavy metal ions. In addition, a yeast biosorbent for biosorption and recovery of molybdate ions was constructed by cell surface display of molybdate-binding protein (ModE). The metal biosorption ability of cell surface-engineered yeasts relies upon features of the displayed metal-binding proteins and natural properties of particular cell wall. Metal-binding proteins with a capacity to form selective coordination spheres and provide tailored biosorption could be generated by direct screening a mutant library with combinatorial mutations in the metal recognition domain at the yeast cell wall background. Therefore, generation of novel metal-binding proteins and molecular breeding of yeast biosorbents showing selective biosorption can be concurrently achieved by cell surface engineering.