Optimization Of The Screening Of Algicidal Bacterium And Study On The Characteristics Of Algicidal Effect Of Strain W5

Microcystis water-bloom is a serious ecological problem. The bio-control, microbio-control is the research hot spot these years. Now more attentions have focused on the issue that algae-lysing bacteria act as a possible factor to mitigate the adverse effects of HABs.In order to increase the efficiency of algicidal bacteria isolation, the components of minimal medium for isolation of algicidal bacteria were tested for the effection growth of Microcystis aeruginosa DS and a modified minimal medium was established.The results indicated that glucose at the concentration of 01⁰.4g·L^-1 in minimal medium inhibited the growth of Microcystis aeruginosa DS, and a modified minimal medium was developed using sodium citrate instead of glucose as carbon sourse. On modified medium algicidal bacteria could be successfully isolated directly from field sample in 1 week. Microcystis aeruginosa DS could grow well on modified medium and the algicidal materials were secreted into medium by bacteria and the growth medium could be directly used for algicidal test.By the modified minimal medium, two strains algae-lysing bacteria were obtained from the pond of JieFang park in Wuhan, and more research were couducted on the strain W5. The results are as follows:(1) the strain W5 could effectively inhibit the growth of on Microcystis aeruginasa, but do little harm to Anabana flosaquaeand, Synechococcus cedrorum IU1191. the fermentation broth also had the excellent lytic effec in the mode experment of outdoors;(2) the strain W5 gave lethal effects on cyanobacteria by means of extracellular products, which were secreted from the stationary stage and reached the peak value at the metaphas stage. When the concertration of the strain W5 was 5× 10⁷ cfu·mL^-1 , the extracellular products made the removal of Microcystis aeruginasa to 80% after 6 days;(3) the extracellular active substance of W5 were water-soluble but not soluble in normal organic solvents. The active substance also showed strong temperature stability, it could keep algicidal activity when autoclaved at 121 ℃ for 30 min. However, this algicidal substance was unstable at different acid and alkali concentration, it could improve algicidal activity at neutral, alkaline, but reduce algicidal activity at high acid concentration;(4) according to the studies on the mophorlogical characters, the physilogical, biochemical characters and the sequence analysis of 16S rDNA of strain W5, it was identified as a Enterobacter aerogenes.