Abstract: One strain, named as Bacillus sp. F2, with the flocculent ability as high as 84%, was separated. Flocculent genomic library was constructed and a Bacillus coli. Positive clone FC2, which could express flocculent activity, was acquired after selection. The 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%), which demonstrated that FC2's flocculent characteristics inherited from the original flocculent bacterium F2. By adopting the tapping mode AFM, light microscope technique and ζ 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 to which fermented liquid with cloning bacterium FC2 was added had larger flocculent gel and more compact spherical structure, and the surface was rough with high degree concave and convex, had large specific surface area and strong adsorption ability to the suspending particles in the solution. After delivering 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, this indicates 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 favorable pollution removal capability of FC2's fermented liquid. The results of ζ-potential test illustrates that the intensity of electrovalent bond was different, resulting in various flocculent morphology, which provided significant evidences for studying flocculent mechanisms of biofloculant.

Key words: Flocculent gene, Genomic library, AFM, ζ-Potential, Microtopography, Adsoption