Firstly, we need to identify that OprF-3* LBT4 and OpRF-Sitag are expressed on the surface of the E. coli. We concentrated cell culture solution of induced test and not induced BL21 cells, and then separate the protein of the whole cell by SDS-PAGE.

Figure 1 shows an obvious ~33kDa protein bands in test lane, which cannot be found in the control lane. This result proves that the test BL21 can produce OprF-3* LBT 4.

Figure 2 shows an obvious ~57kDa protein bands in test lane, which cannot be found in the not induced lane. This result proves that the test BL21 can produce OprF-Sitag.

1.2 Verification of Cell Surface Display System

Figure 3 shows the result of our verification of our cell surface display system. Some cells can show a considerable fluorescent intensity, while some perform partial or weak fluorescence which can not be detected by our microscope camera. But this result still successfully demonstrated the cell surface display of our LBTs.

1.3 Precipitation titration detection

In order to test our capture system, we test our engineering bacteria with a series of different concentration of terbium ions. After doing a precipitation titration, we got some exciting results.

Figure 4 shows that it is significant difference in the amount of precipitation. The amount of precipitation in WT group(with distilled water added) is much less than that in the test group.

To get some more detailed and convincing results, we did a precipitation-dissolving titration with hydrochloric acid. Figure 5 can show a result that the test group(with our engineered bacteria) is much different from the control group(with distilled water added). After our engineered bacteria work a while in sample, the terbium ions concentration is significantly reduced.