| In recent years, Bacillus had got more and more attention as they decomposed and transformed organics and water pollutants such as nitrogen and phosphorus to inhibit the growth of cyanobacteria. It made great significance to maintain the ecological balance of aquaculture water and repair degraded ecosystem.This paper isolated one of the most functional strains from the eutrophicated aquaculture water to inhibit the growth of algae which called SK-1. The strain was authenticated with physiological and biochemical characteristics and 16s rDNA sequence analysis. Furthermore, we studied the growth characteristics of SK-1 strain, the effect of thallus and metabolites of SK-1 to prevent the growth of Microcystis aeruginosa, features of metabolites. We also researched the competition of nutrients and the effect of each other when SK-1 was coexist with Microcystin aeruginosa, the application security of SK-1 to aquaculture organism in aquaculture water and the biological control of cyanobacteria blooms of SK-1. The results show that:1. After 10 days’ algal inhibiting test, we found that the inhibition rate of SK-1 strain to Microcystis aeruginosa was 59.5%, which has great difference with other four bacterial strains. So we choose it as algal inhibiting bacteria to study futher.2. We authenticated the strain with physiological and biochemical characteristics and 16s rDNA sequence analysis. It turned out that the SK-1 strain belongs to the kind of the bacillus (Bacillus laterosporus).3. The optimum growth temperature of SK-1 was 30℃, the optimum pH value of SK-1 was 7.5, the best thermostatic cultivation rate of SK-1 was 150 r·min-1, the logarithmic phase of SK-1 was between 2-20 h.4. Preliminary study revealed that the strain SK-1 could not kill the algae cells by itself but it could secrete some extracellular materials which played a role of algae inhibiting and it has a significant relationship between concentration and effect. At a certain concentration range, the greater dose, the more pronounced algae inhibiting effect Through the analysis of the active material properties, we found that protein was an important part of it and it had hydrophilicity.5. The medium of SK-1 had certain inhibition to the growth of Microcystis aeruginosa, it also had a slight interference impact on the algal inhibiting effect of filtrate, but the impact has nature and significant difference (P< 0.01) with the effect of sterile clear filtrate. To eliminate the interference effects, the addition amount of algal inhibiting medium in the study was less than 6%. The test time was controlled within 6 days.6. The results showed that estimated ratio of C:N:P 250:10:1 was obtained in co-substrates system by adding glucose and ammonia nitrogen to the eutrophic aquatic water. In the co-substrates, the algae and bacteria had different effect of stress at their growth phase. The strain SK-1 at stable phase had the best inhibitory effect on Microcystis aeruginosa at early growth stage and at a certain concentration range, the greater dose, the more pronounced algae inhibiting effect. The results indicated that the strain SK-1 inhibited the growth of Microcystis aeruginosa by nutrient competition and secretion of extracellular materials at different proportion in different growth phase of algae and bacteria. So in order to obtain better ecological effect, the bacteria should be cultivated prior to algae outbreak.7. After 10 days test, zebrafish growed well in the water whose bacterium solution of SK-1 was 5,10 and 20 g·L-1, which showed that SK-1 had no acute and subacute toxicity to zebrafish. Zebrafish embryos hadn’t die in the same conditions within 96 hours, the hatching rate was 100% in 72 hours.The number of heartbeat in zebrafish embryos had no significant difference compared with the control group (P>0.05), which showed that Bacillus laterosporus SK-1 had no toxic effects to zebrafish embryos. The studies showed that the concentration of Bacillus laterosporus in this test could ensure security.8. The SK-1 (viable cells count≥ 108 CFU·mL-1) was added to eutrophic freshwater pond by the amount of 0.50,1.00 mg·L-1. The TN, TP and permanganate index had declined in 60 days, in the meantime the growth of algae was controlled. The Shannon-Weaver index was significantly increased, which showed that the algal community structure had improved.Studies had shown that Bacillus laterosporus SK-1 had a good prospect in repairing the aquatic ecosystems of eutrophicated aquaculture water. It could open up a new way to control cyanobacteria blooms in aquaculture water. |
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