| One strain, named as Bacillus sp. F2, of which flocculent ability can reach 84%, was separated. Flocculent genomic library was constructed. The total genomic DNA of F2 was extracted. It was partly digested by restriction enzyme Sau3AI and then was connected with carrier PUC19DNA which was totally digested by restriction enzyme BamHI and further was converted to competent cells JM109.These cells were smeared on the ampicillin substrate. After one night culture, we selected them by white-blue spot screening and constructed the flocculent genomic library. The library included 3.5×104 recons and the titre was 3.5×105 dpfu/mL. strain of Escherichia coli. positive clone FC2, which could express flocculent activity, was acquired after selection. Flocculent tests showed that the flocculent efficiency of FC2 was 90%, which was slightly higher than the original flocculent bacterium F2 and greatly higher than the competent cell JM109 (6.9%). It demonstrated that FC2's flocculent characteristic inherited from the original flocculent bacterium F2. By adopting the tapping mode AFM and Zeta-potential test, the flocculent microtopography of FC2, F2 and pure kaolin suspending solution was identified. The AFM study revealed that, compared to the kaolin suspending solution with and without F2's fermented liquid, the kaolin suspending solution which has cloning bacterium FC2's fermented liquid had larger flocculent gel and more compact spherical structure, and the surface was rough with high degree concave and convex, and had large specific surface area and strong adsorption ability to the suspending particles in the solution. After adding the fermented solution of cloning bacterium FC2 into kaolin suspending solution, the amorphous and incompact flocculent particles transformed into spherical structure which was compact and had even horizontal dimension, which indicated that the agglutinin in FC2's fermented liquid could easily take kaolin suspending particles as its adsorption core and adsorbed on its surface and the flocculent efficiency was about 90%, which gave further confirmation to the great pollution removal capability of FC2's fermented liquid. The results of Zeta-potential test illustrated that the intensity of electrovalent bond was different, resulting in various flocculent morphology, which provided significant evidences for studying flocculent mechanisms of biofloculant. |
