Identification And Characterization Of A Novel Bacillus Methylotrophicus With High Flocculating Activity

In this study, a novel bioflocculant-producing strain was derived Bacillus methylotrophicus by 16S rDNA and gyrase B sequencing analysis, as well as morpHological, pHysiological and biochemical characterizations. The component of bioflocculant ?i.e., MBF412? secreted by strain C412 is composed of 57.3% polysaccharides and 1.7% protein. The results of GPC indicated that the average molecular weight of the bioflocculant was 3.47×105 g/mol.The bioflocculant production ?4.25 g/L? was associated with the bacterial growth process, and the maximum flocculating activity of 98.27% were achieved using an optimized culture medium by response surface methodology containing ?per liter? soluble starch ?19.73 g?, beef extract ?1.35 g?, ?NH₄?₂SO₄?3.05 g?, NaCl?1 g?, KH₂PO₄?2 g?, K₂HPO₄?5 g?, and MgSO₄?0.05 g? at pH 7.63. Batch fermentation of strain C412 in high-cell density cultures showed shorter generation times in a 1.5 L fermentor ?2?6 h? than in a shake-flask ?13?17h?. This significant decrease offers a cost-effective method for large-scale bioflocculant production. The bioflocculant is thermostable over a broad temperature range ?4 ? to 60 ?? and has wide pH receptivity ?4 to 13?, which may be attributed to its main components, namely, polysaccharides and polar functional groups. Relative flocculent-gene expression in novel B. methylotrophicus C412 was studied by quantitative reverse transcription PCR. The relationship between the expression levels of katE, pepT, and scrR and flocculating activity was established. Furthermore, a two-step flocculation mechanism ?i.e., charge neutralization and bridging mechanism? was proposed for the settlement process based on zeta potential analysis. This study also demonstrated the potential of MBF412 for treating industrial wastewater.