Generation of metal-binding staphylococci through surface display of combinatorially engineered cellulose-binding domains

Ni2+-binding staphylococci were generated through surface display of combin atorially engineered variants of a fungal cellulose-binding domain (CBD) fr om Trichoderma reesei cellulase CeI7A. Novel CBD variants were generated by combinatorial protein engineering through the randomization of 11 amino ac id positions, and eight potentially Ni2+-binding CBDs were selected by phag e display technology. These new variants were subsequently genetically intr oduced into chimeric surface proteins for surface display on Staphylococcus carnosus cells. The expressed chimeric proteins were shown to be properly targeted to the cell wall of S. carnosus cells, since full-length proteins could be extracted and affinity purified. Surface accessibility for the chi meric proteins was demonstrated, and furthermore, the engineered CBDs, now devoid of cellulose-binding capacity, were shown to be functional with rega rd to metal binding, since the recombinant staphylococci had gained Ni2+-bi nding capacity. Potential environmental applications for such tailor-made m etal-binding bacteria as bioadsorbents in biofilters or biosensors are disc ussed.