| Recently,eutrophication and harmful algae blooms have attracted more concern in China due to their adverse effects on the environment.Therefore,it is imperative to seek effective methods to prevent algae blooms.Algae-lysing bacteria,as the biology of removing alage have attracted more attention because the physical,chemical and other biological methods are not good at removing algae.Moreover,algae-lysing bacteria has broad application prospect.In this study,Microcystis aeruginosa,the common algae during harmful algae blooms was regarded as the research object.Four strains of algae-lysing bacteria were isolated from different water bodies and the decomposing effects and characteristics of algae-lysing bacteria against Microcystis aeruginosa were studied in detail.The algae-lysing mechanisms were discussed intially and the 16S rDNA sequence analytical method was used to identify four strains of algae-lysing bacteria.The main contents and achievements of this study are as follows.Several strains of algae-lysing bacteria were isolated respectively from activated sludge acclimated by Microcystis aeruginosa,yellowish Microcystis aeruginosa,and lakes in algae blooms.Among these algae-lysing bacteria,the four strains numbered T5,H1,K2,D1 had good algae-lysing effects and were studied in detail.The toxicity detecting experiment showed that the 4 strains did not release toxicity.The algae-lysing characteristics of the bacteria against Microcystis aeruginosa showed that the algae and bacterial cell concentrations influenced algae-lysing effects deeply.The initial bacterial and algal cell densities strongly influence the removal rates of chlorophyllα.The greater the initial bacterial cell density,the faster the degradation of chlorophyllα.The greater the initial algal cell density,the slower the degradation of chlorophyllα.The temperature,pH and the illumination also had deep influence on the algae-lysing effects.The higher of the temperature,the faster of the degradation of chlorophyllα.The removal rates of the 4 strains of algae-lysing bacteria on Microcystis aeruginosa between 30℃ and 35℃.The algae-lysing effects of 4 strains when pH was 7.2,7.6,and 8.1 showed that the 4 strain of bacteria had the same algae-lysing rules and the algae-lysing effects were pH 7.6＞pH 7.2＞pH 8.1.The algae-lysing effects of 4 strains under different light density were tested.and the results showed the algae-lysing effects in darkness were better than in illumination.The study of the mechanisms of 4 strains algae-lysing bacteria on Microcystis aeruginosa showed that the strain T5,H1,K2,D1 all removed algae by not directly but by secreting metabolites.The metabolites secreted by the strain T5,H1,K2 could bear high temperature and were not protein matter.While the metabolites secreted by the strain D1 were composed by protein matter and non-protein matter.The degradation of algae-lysing bacteria against MC-LR also was studied. According to HPLC testing,the strain T5,H1,K2,D1 had good removal on MC-LR and the removal rate were 73.4%,42.1%,65%and 70.4%respectively after 5 days.If the enzyme inhibitors were added into the system,MC-LR could not be degraraded by the algicidal bacteria.Therefore,the 4 strains all degraraded MC-LR by enzyme.The 4 strains were identified by the sequence analysis of 16S rDNA.The DNA sequence similarity analysis with the obtained sequences in Genbank showed that the strain T5 shared 94%sequence homology with one strain of Ochrobactrum sp.,the strain H1 shared 100%sequence homology with one strain of Brevibacillus parabrevis,the strain K2 shared 99%sequence homology with one strain of Ochrobactrum sp.and the strain D1 shared 97%sequence homology with several strains of Brevibacillus sp..According to the results,the strain T5 and K2 belonged to Ochrobactrum sp.and the strain H1 and D1 belonged to Brevibacillus sp..The accession numbers of the sequences in Genbank were EU586033(T5),EU594550(H1),EU594551(K2),EU593881(D1). |
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