The EP-PCR library was transformed into BL21 E. coli cells, and library expression was induced with 50 μM IPTG. To determine the number of cells that survived the 50mM selenite challenge, serial dilutions of 10 μL in triplicate were plated on LB-agar at 24 h intervals allowing determination of the CFU count of the culture. Similarly to earlier experiments, CFU count of the library decreased several orders of magnitude through the first day of selection, followed by rebound growth in the following days. As is shown in Figure , we infer that an initial drop in CFU correlates to a loss in the overall library diversity. Subsequent cell proliferation therefore occurs from a 'fitter' subsection of the initial library, which forms the basis of evolutionary selection.