Abstract
The present study deals with inactivating harmful algae blooms (HABs) in the fresh water samples by using algicidal bacteria (Bacillus subtilis). The inactivation process was performed under the direct sunlight and optimized using central composite design (CCD) based on three independent factors included time (1-6 h), bacterial supernatant dosage (1-10 mL 100 mL(-1)) and pH (5-8). The results revealed that the maximum inactivation of HABs was achieved with 1.61 mL 100 mL(-1), within 6 h and pH 8, the reduction was 6 vs. 5.78 log and 90.22 vs. 87.767% of the chl a reduction (observed and predicted, respectively, R-2 = 0.976). The inactivation mechanism was explained based on the analysis of untreated and treated HABs cells by field emission scanning electron microscope with energy dispersive X-ray spectroscopy (FESEM-EDX), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy which revealed a damage in the cell wall structure due to the effect of algicidal substances. Moreover, FTIR analysis showed that the damaging of HABs was due to the adverse effect of algicidal substance, which lead to the damage of protein and carbohydrate structure of the HABs cell wall. These results further demonstrate that the algicidal bacteria can effectively inhibit HABs cells in the freshwater.