Extraction of flocculants from a strain of Bacillus thuringiensis and analysis of their properties

In a preliminary screening study, our laboratory isolated from the biofloc in aquaculture waters a strain of Bacillus thuringiensis, which produced highly efficient bio-flocculants. In the present study, we extracted the crude flocculants from this strain and analyzed their properties. Distribution analysis indicated that the flocculants were mainly distributed in the supernatant of the fermentation liquid. The flocculants were extracted using an ethanol extraction method, and the chemical compositions and morphology of the crude flocculants were analyzed using the Molish reaction, Fehling reaction, ninhydrin reaction, biuret reaction, phenol-sulfuric acid assay, Coomassie brilliant blue staining, ultraviolet scanning, infrared scanning and scanning electron microscopy. The carbohydrate composition of the polysaccharides in the flocculants was analyzed with thin layer chromatography. The results indicated that flocculants were solid substances with an ivory white color and their texture was loose and soft. Visualization under scanning electron microscopy revealed that their ultra-morphology consisted of small, long and fiber-like shapes. Chemical and physical analyses indicated that polysaccharides accounted for 34.5% of the components in the crude flocculants. The monosaccharides present in crude flocculants included mainly glucose, galactose and mannitose.