| With the increasingly serious eutrophication and frequent outbreaks of harmful cyanobacterial blooms in worldwide waterbodies, it is in urgent need of exploring effective methods to prevent algal bloom.The use of algicidal bacteria, which is characterized by cheapness,safety and undestroying as a new method of controlling algae, has become one of the hotspots in biological control of algae.In this study, algicidal effect of N1strain on Microcystis aeruginosa (M. aeruginosa), bacteria cell culture, separation of algicidal components and the inhibiting mechanism were studied, and the conclusions were described as below.(1) Detecting the algicidal activity of extracellular secretion to screen the strongest strains from five strains of algicidal bacteria. Our experiments showed that the extracellular secretory of N1, N4, N5, W7and Y3caused lysis were79.68%,64.71%,50.80%,37.79%and73.26%, respectively. Based on the existing research, the author studied N1extracellular secretory that showed the strongest activity of lysing M. aeruginosa when the following conditions were used for culture:at72h, pH=7.5,28℃.(2) After high temperature treatment, the algal activity of N1bacterial extracellular secretion was still high. Low algicidal activity of the bacteria was foud after crushing, after heat treatment, no inhibition of M. aeruginosa. It's shown that the main algal composition was the bacterial extracellular secretion, and good thermal stability.(3) The extract from bacteria N1extracellular secretory was preliminarily separated into threer parts by liquid-liquid extraction with ethylacetate, n-butanol and aqueous phase. The medium effective concentrations (EC50) of ethylacetate and n-butanol on M. aeruginosa were47.6and71.5mg/L, respectively. Purificated by column chromatograghy, TLC and HPLC analysis, which combined the same or similar componets, then the extract was treated by active track.The activity of fraction II and V shown the stronger activity with M. aeruginosa. After further separation and purification, the two more active compounds were extracted,isolated and purified,as unsaturated fatty acid (N1-1B and N1-5D)(4) A preliminary inquiry showed that:N1-1B and N1-5D could reduce the number of algal cells and the content of chl-a, N1-1B stimulated chl-a content of single cells to increase significantly than the control. It could be deduced that N1-1B inhibited algal cell division, and resulted in the accumulation of pigment within the cell. The two compounds inhibited the activity of superoxide dismutase (SOD), and led to the increasing of lipid peroxidation product malondialdehyde (MDA) content, destroy the antioxidant defense system, lead to lipid peroxidation and oxidative damage, and inhibit the metabolism processes of M. aeruginosa, eventually result in the death of the algal cell. MDA levels of algal cells treated with N1-5D were lower than the N1-1B treatment. Content of carotenoid combined with N1-5D changed little, and it was showed that probably in the early stages of treatment carotenoids could reduce the level of reactive oxygen species to a certain extent so as to reduce the damage of M.aeruginos after N1-5D stress. As a result, the72h-ECsoof M. aeruginosa. after N1-5D treatment were far higher than ones treated with N1-1B.Separation of the two fatty acids of algal compounds were purified from the Dianchi Lake bacteria dominant species in the fermentation broth of strain N1and showed good activity. It needs further research for more development in this field, and this observation can provide some guidance on application of this method to control algae in the future. |
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