Screening of Seawater Compound Bioflocculant Producing Bacterial Strains and Optimization of Their Culture Medium

Compared with single bioflocculant, compound bioflocculant (CBF) normally has more stable and higher flocculation efficiencies. In order to produce a new compound bioflocculant, four bacterial strains with relative high rate of flocculation were selected from the coastal zone sediment, all of which were determined as Pseudomonas sp. by 16S rRNA sequencing. Through compounding, the ideal proportion of compound bioflocculant consisting of two bacterial strains (F5 ∶ M5) was determined as 1 ∶ 2, resulting in 6% increase in terms of flocculation rate. The significant fermentation factors in culture media and their limitations were investigated via single factor experiments and Plackett-Burman design, obtaining four key variables, MgSO₄, (NH₄)₂SO₄, sucrose and peptone, which were further optimized by response surface methodology (RSM) for their optimal concentrations. Finally, the ideal culture medium was determined, containing (NH₄)₂SO₄ 0.523 g, MgSO4 3.7 g, sucrose 12.82 g, K₂HPO₄ 4 g, KH₂PO₄ 3 g, NaCl 33 g, and deionized water 1 L. The flocculation rate of experimental data (88.92) agreed well with the model prediction, which was 16.60 higher than original rate.