| Human beings discharge other urban domestic sewage and industrial wastewater with nitrogen and phosphorus into the water,so that excess nitrogen and phosphorus appear in the water.It promote excessive growth of algae in the water,then leading to water blooms in fresh water and red tide in ocean.It is called water eutrophication.Therefore,the control of cyanobacteria blooms is the main way to solve the water eutrophication.The governance of cyanobacteria blooms generally have physical,chemical and biological methods,but the first two operations are not easy,costly and result in secondary pollution.Biological methods of cyanobacteria blooms become the main means.At present,algae-lysing methods of an algicidal bacterium is studied by domestic and foreign researchers and applied in reality.An algicidal bacterium strain named as WJ6 with algicidal activity against the toxic algae Microcystis aeruginosa was isolated from the eutrophication of water bodies in this paper.Morphological observation,physiological and biochemical identification and 16S rRNA sequence were conducted.The algae-lysing effect of different culture periods,concentrations of bacterium and environmental factors was studied to analyze the dissolubility of the strain WJ6.The algae-lysing means of the bacterium and the properties of the extracellular active substances were also investigated,and the algae products produced during the algae-lysing were analyzed.The main results are as follows:1.An algicidal bacterium strain named as WJ6 was isolated from the eutrophication of water bodies.It was Gram-negative and single colony was red,small and round.Its edge was regular and the surface was smooth and moist.The results of physiological and biochemical identification of the strain WJ6 were:the results of methyl red,hydrogen peroxide and gelatin liquefaction test were positive;The VP test result was negative;Glycolysis test result was the fermentation type.It used glucose,sucrose,mannitol,lactose and reduce nitrate.Based on morphological observation,physiological and biochemical experiments and 16S rRNA gene sequence analysis,the strain WJ6 belongs to Serratia sp.Genbank accession number is KY462187.2.The strain WJ6 in logarithmic phase could dissolve Microcystis aeruginosa with a removal rate of 87.50%±2.41%.The sterile condensed bacteria-free filtrated with the concentration more than 1.4×109 CFU/ml gave the highest removal rate of95.69%±1.00%.Under the condition of 30℃and pH8,the removal rate was 99.48%±0.21%and 92.47%±4.02%,respectively.The inhibition effect of the strain WJ6 on Microcystis aeruginosa was:full darkness>12L/12D>full light,with the highest rate of 97.06%±1.20%in the full darkness condition.The algae-lysing bacteria was cultured in 5 different cultures（liquid beef extract peptone medium,LB medium,modified basic medium,BG11 medium and Chalm culture medium）to explore the algicidal effect of algae-lysing bacteria.The algae-lysing effect of the liquid beef extract peptone medium was the best,the removal rate was 96.00%±1.87%.In the medium,adding different concentrations of NH4Cl and NaCl,we can see that when the ammonium ion concentration is greater than 2 mol/L,in a certain range,the removal rate of the algicidal bacterium was 98.33%±1.67%.When the salinity is0.5%,the higher removal rate was 92.77%±2.95%.3.The algicidal mode of the strain WJ6 with algicidal activity against the toxic algae Microcystis aeruginosa was in an indirect way.The active substance of the extracellular fluid secretion from algicidal bacteria was a molecular weight more than8 KD substance,and the active substance is a mixture of substances.The extracellular fluid secretion was deposited by ethyl alcohol and the removal rate of sedimentation section is greater than supernatant fraction,up 82.72%±1.75%.The removal rate was stronger with the condition of 25℃,pH8 and they were 92.97%±3.32%and 94.69%±2.17%.The extracellular secretion of the active substance had a higher antioxidant activity.4.The algae products were analyzed in different concentrations of bacterium on the algae removal of Microcystis aeruginosa.The UV absorption peaks appeared at438 nm,619-628 nm and 673-677 nm,respectively.The peaks were similar in different concentration groups.The peak intensity increased with the increase of the concentration of bacterium.After scanning by infrared spectroscopy,it was found that the algae products contain N-H,C-H,O=N-O-（-NO2）and C-O.The three-dimensional fluorescence peaks of the algae products in different concentrations were similar,but the peak intensity of the experimental group was higher than that of the control group.With the dilution ratio increasing,the peak intensity was gradually decreasing.Then it led to the concentration of the algae product decreased.The main algicidal product was a tryptophan substance.The correlation between the fluorescence intensity and the concentration of the algae was analyzed.The higher the concentration of the bacterium was,the more obvious the algae-lysing effect was. |
