|Other Abstract||The occurence of harmful algal blooms (HAB) widely in the world has recently increased as a global environment problem, which affects people's life, health, productive activities and the sustainable development of ecosystems severely. It is necessary to look for some effective methods to control HAB. Algae-lysing bacteria have been regarded as a candidative measure of microbiological control on water bloom with more and more concern. In this study, two high-effect algae-lysing bacteria were isolated and purified from Lake Dianchi. The effect, host range, biosafety, lysing mechanism, culture condtion and application test of these two algae-lysing bacteria were analyzed. Results are as the followings.
1) Two algae-lysing bacteria were isolated from the heavy cyanobacterial blooming area of Lake Dianchi, which were labeled as DC-L5 and DC-L14. They were identified as Bacillus pumilus and Lysinibacillus fusiformiseir respectively by means of morphological observation and 16S rDNA sequence analysis in the CCTCC. Toxicity test with mouse primarily showed that the two bacterial strains were non-toxic. For the lysing effect, average reduction rates of Chlorophyll a of 62.25% and 67.20% in cultures of Microcystis viridis, Microcystis wesenbergii, Aphanizomenon flos-aquae and Anabaena flos-aquae with the two bacteria in 4 days were observed.
2) The strongest algae-lytic abilities were found in the log and stationary phases of DC-L5 and DC-L14 cultures, Chlorophyll a contents in cultures of Microcystis aeruginosa reduced by 83.33% and 82.10% respectively in 5 days . Strain DC-L5 could directly cause the cyanobacterial cells agglomerated, sinked down and further lysed; while this strain could excrete extra-cellular substances able to lysing cyanobacterial cells. With wild Microcystis aeruginosa bloom, Strain DC-L5 firstly disaggregated the cyanobacterial colony, reduced the floatability, degraded the pigments and then released inclusions of algal cells. Extracellular substance produced by strain DC-L14 was thermostable, and high temperature possibly reinforced the release of this kind of substance.
3) For the cultivation of DC-L4 in broth medium, the optimal pH was 7.5 and cultural temperature was 35 ℃. Test of adding carbon source, and inorganic salt into the culture, showed that, additional glucose (1%, w/w), MgSO4 (0.1%) and KH2PO4 (0.1%) could enhance the cell number of DC-L14 by 24.53%, 14.94% and 12.46% respectively, and reduced the Chl.a content of bloom by 11.10%, 2.75% and 3.80% in correspondance. Thus, it can be taken in account that, the recipe of fermentation medium would be optimized through the uniform-design. A suitable fermentation condition for culture of DC-L14 could be optimalized as adding 1%glucose, 0.1 %MgSO4 and 0.2% KH2PO4 into broth medium, by which, the culture of DC-L14 could increase by 20.36% and the Chl.a content of bloom could reduced by 8.86%.
4) The algae-lysing results showed that, DC-L5 was a well algae-lytic strain against Microcystis aeruginosa both in uni-algal culture and with wild bloom from lake, but more obvious Chl.a decrese was observed in the former case than in the latter one. On the other hand, results showed that, algae-lysing caused changes in water chemistry as, adding strain DC-L5 into uni-algal culture of and the wild bloom dominant with Microcystis aeruginosa, the content of TN, TP and CODMn increased soon, then the content of TP remained at a high level, meanwhile the content of TN and CODMn reduced obviousely. Algae-lysing results in an experimental enclosure in Lake Dianchi showed that DC-L5 could reduce the content of Chl.a and improve the SD in the water body, the best algae-lytic effect displayed on the 4th day, and the effect could last for 13 days.|