Optimization of the production of exopolysaccharides by Bacillus thuringiensis 27 in sand biological soil crusts and its bioflocculant activity

To improve the yield of exopolysaccharides (EPS) by Bacillus thuringiensis 27 from sand biological soil crusts in Gurban Tonggut Desert, Xinjiang, China and to analyze its bioflocculant activity, orthogonal matrix method was used and this method enabled us to obtain maximum EPS production. By studying the optimal medium condition of beef extract 3 g/l, peptone 10 g/l, maltose 40 g/l, and NaCl 4g/l we observed that the optimal medium condition was pH 6.0, incolum size 8%, liquid volume 40 ml in 200 ml flak and temperature 28°C. The maximum EPS production was 20.19 g/l which is about five times more than that at the basal condition. Furthermore, results obtained indicated that the flocculation activity of the extracellular polymer can be achieved at over 80.4% in kaolin suspension and this occurred at a concentration of 0.4 mg/l. This paper describes the optimum condition of exopolysaccharides production by Bacillus thuringiensis 27 and showed that exopolysaccharides had high bioflocculant activity. This work provides a scientific foundation to explore new exopolysaccharides and bioflocculation in sand biological soil crusts. Maximum production of exopolysacchaides under the optimal medium and condition can be achieved and exopolysaccharides have high bioflocculating activity in kaolin system.   Key words: Biological soil crusts, exopolysaccharides, flocculation, optimization, Bacillus