Screening Of A Novel Bioflocculant-producing Strain Of Bacillus Sp. And Its Initial Application In Carp Farming

As an alternative in place of existing chemical synthetic flocculants, bioflocculants have many advantages, such as biodegradability, harmlessness and lack of secondary pollution of their degradative intermediates. Bioflocculants have great application potential in industrial processes, such as wastewater treatment, drinking water purification, downstream processes of food and fermentation, removal of heavy mental, dyes and so on. In this paper, we concentrated on studying screening for bioflocculant-producing Bacillus sp., characteristics of the bioflocculant as well as its initial application in carp farming, and the experiment results are summarized as follow:(1) Thirty-eight bioflocculant-producing strains were screened out from six samples by streak plate method. Among them, a strain MBFF6(the bioflocculant produced named BF6) exhibited the highest flocculating activity (over95%) to kaolin suspension which came from soil samples in the campus of Sichuan Agricultural University. And it was identified as Bacillus megaterium by16S rDNA sequence and its biochemical and physiological characteristics.(2) The effect of culture time, carbon source, nitrogen source, C/N ratio, pH, metal ions, cultural temperature and inoculum size on bioflocculant production by Bacillus megaterium MBFF6was investigated by signal factor test. At the same time, the influencing factors like fermentation broth dosage, Ca2+concentration and pH on the flocculation were investigated. The results revealed that the optimal culture conditions for B. megaterium MBFF6production were glucose5g/L, peptone0.5g/L, K2HPO45g/L, KH2PO42g/L, MgSO4·7H2O0.2g/L, pH7, inoculum size2%(v/v), initial pH7.0, culture temperature30℃, and shaking speed150r/min for24h. Studies on flocculating properties showed that the bioflocculant produced by B. megaterium MBFF6was an extracellular polymer, it was mostly distributed in cell-free supernatant; the bioflocculant MBFF6was stable at60～100℃; the highest flocculating rate was95.7%observed at MBFF6dosage2mL, CaCl2dosage5mL and pH7.0.(3) The bioflocculant BF6was purified from supernatant by ethanol precipitation. The production of bioflocculant BF6from fermentation broth was1.28g/L and it was a white powdery substance. The chemical and structural characteristics of bioflocculant BF6were also analyzed. Chemical analysis showed that the main compositions of BF6were polysaccharide (50.79%) and protein (10.90%). Fourier-transform infrared (FTIR) indicated the presence of hydroxyl, amino, carboxyl, and methoxy-groups in bioflocculant BF6(4) The results of fermentation from B. megaterium MBFF6on treatment the aquatic water indicated that the trail treated with B. megaterium could significantly (p<0.05) decrease the concentration of ammonia nitrogen, nitrite, COD and increase transparency in aquatic water comparing with the control. The changes of pH value were lower than that of the control. Mice were given0.5ml cell broth which concentration was1×1010cfu/mL of B. megaterium MBFF6and original concentration of supernanant by oral way separately. The aquatic water of carps contained1×108cfu/mL of B. megaterium MBFF6. After14days, the result showed that B. megaterium and the biofloccuant produced by it were very secure for mice and carps.