Removal of Microcystis aeruginosa cells using the dead cells of a marine filamentous bacterium, Aureispira sp. CCB-QB1

Inorganic and synthetic flocculants are widely investigated for removing harmful microalgae, such as Microcystis aeruginosa. However, their toxicity and non-biodegradability are shortcomings. Bioflocculants based on extracellular polysaccharides have attracted much attention as alternative flocculants. However, its high production cost is a limiting factor for applying bioflocculants. Here, we investigate the potential of the dead cells of a marine filamentous bacterium, Aureispira sp. CCB-QB1, as a novel flocculant on M. aeruginosa cells. The removal efficiency of M. aeruginosa cells by the dead cells was measured by mixing and shaking both components in a buffer with 5 mM CaCl(2) in different incubation times and concentrations of the dead cells. After that, the minimum effective concentration of CaCl(2) was determined. The combination effect of FeCl(3) and the dead cells on the removal efficiency was tested. The structure of cell aggregates consisted of the dead cells and M. aeruginosa cells were also observed using a scanning electron microscope. The maximum removal efficiency (75.39%) was reached within 3 min in the presence of CaCl(2) when 5 mg/ml of the dead cells (wet cells) were added. The optimal concentration of CaCl(2) was 5 mM. The combination of the dead cells and a low concentration of FeCl(3) (10 mg/L) with 5 mM of CaCl(2) significantly improved the removal efficiency by about 1.2 times (P < 0.05). This result indicates that the combination usage of the dead cells can reduce the use of FeCl(3). These results indicated that the dead cells could potentially be a novel biolfocculant to remove M. aeruginosa cells.