Stduies On Pheromonicin Selectively Inhibition The Growth Of Cyanobacteria

Along with the development of modern civilization and utilization of natural resources, a large amount of untreated wastewater discharged directly into the water, causing waterbody entrophication that nitrogen, phosphorus and other nutrients enriched, so as that eutrophic lakes intensify, and provide the conditions for cyanobacteria-bloom outbreaks. Many of large and medium sized lakes are faced with the problem of cyanobacterial blooms, Frequent outbreaks of cyanobacterial blooms not only seriously affect the safety of the ecosystem, but also pose serious health threats to human beings. Given that cyanobacterial blooms threatening to both the environment and human beings, controlling and removing them in freshwater is extremely important. A lot of studies have been performed by many scholars and experts form domestic and foreignin, and a large number of scientific programs focusing on governing cyanobacteria blooms have been proposed. In practice, most established methods on governing water blooms had not specificity on cyanobacteria, and even showed the toxicity to other algae and animals in freshwater, leading to biodiversity decline, and thus may undermine the structure and function of ecosystems. Therefore, exploring and finding out safe algal methods is necessary and urgent.Recently, Pheromonicin which is a kind of fusion protein with specific bactericidal features synthesized by bio-engineering methods, has high specificity in the management of cyanobacteria blooms. The main part of this thesis conducted the experiments on inhibitory effects of Pheromonicin against cyanobacteria, consisting of laboratory and outdoor studies, the results are summarized as below:1. Under the laboratory condition, five common bloom-forming cyanobacterial strains and one green algal strain were selected as the research materials for the Pheromonicin acute toxicity test, as Microcystis aeruginosa(NISE 843), Dolichospermum flos-aquae(CHAB 3530), Aphanizomenon flos-aquae(CHAB 178), Planktothrix agardhil(CHAB 679), Microcystis aeruginose(CHAB EH22) and Scenedesmus quadricauda. The results of the laboratory test indicated that Pheromonicin inhibited the growth of the five cyanobacterial strains specifically, without any significant effect on green algae. The different concentrations of Pheromonicin induced different levels of the inhibiting effect. within a certain range, the effects on inhibiting the growth of the cyanobacterial strains enhanced due to increasing concentration of Pheromonicin. According to the EC50 values of growth inhibition, the variation of sensitivity to Pheromonicin was observed among strains. The result shows that EC50 of Pheromonicin were the increasing order for: Aphanizomenon flos-aquae(CHAB 178), Planktothrix agardhil(CHAB 679), Microcystis aeruginose(CHAB EH22), Microcystis aeruginosa(NISE 843), Dolichospermum flos-aquae(CHAB 3530). 2. Water samples from a microcystis-blooming waterbody were collected and treated in laboratory conditions. The results were similar to that obtained independently in five cyanobacterial strains. showing that the improvement of inhibiting on cyanobacteria coupling with the increasing concentration of Pheromonicin within a certain range. In addition, a phenomenon that the content of microcystin decreased during the test needs further investigation. 3. In a small eutrophic pond, Pheromonicin as algicide was added to remove the cyanobacterial bloom. The results revealed that Pheromonicin pose significant influences on removing the phytoplankton biomass and on reducing the content of chlorophyll a, It also improved the transparency of water column and a significant effect on reducing the total nitrogen and total phosphorus. Moreover the cyanobacteria bloom disappeared over a period of time after the treating. The morphological observation on the phytoplankton strains indicated that Pheromonicin specifically inhibitied cyanobacterial growth and had no influence on eukaryotic algae. 4. Acute toxicity test was performed by adding Pheromonicin in a gradient to the culture of Daphnia magna, The result showed that the mortality of Daphnia magna was not changed for the initial forty-eight hours, which indicateed that Pheromonicin has no toxicity to Daphnia magna.