| Red tide has frequently occurred in recent years. The blooms have seriously endangered fishery production and economic development of coastlands. Research on the mitigation of harmful algal bloom has been attracting increasing international attention. Under the circumstances that physical and chemical control methods to red tide are not effective, the use of algae-lysis bacteria as a new method of red tide control and potential microorganisms, has attracted extensive attention of national and international researchers, and gradually become an intensive area of scientific research in the field of marine environment. In this paper, three algae-lysis bacteria labeled G, Y and W, were isolated from Pearl Sea where red tide often outbreaks. The bacteria had significantly algae-lysing effect on marine alge Phaeocystis globosa Scherffel. For the purpose of exploring a new method to solve the long time problem of P. globosa outbreaks and providing a scientific basis for the control of harmful alga microorganisms in coastal zones, we studied the lysing-process of the three algae-lysis bacteria, morphological changes of the bacteria and P. globosa before and after, the relation between the effect of algae and environmental factors, the relations cycle of fluorescence changes between algae and bacteria, the molecular biology mechanisms of algae-lysing, finally, the fate of bacteria and micro-ecological effects in phycosphere. The main results were as follows:1. Eleven bacterial strains were isolated from red tide-prone areas of Pearl Sea by traditional culture, from which 3 strains with algae-lysing effects, labled G, Y, and W, were selected and confirmed as Gram-positive bacteria, bacillus, in distinctly different morphology patterns. G bacteria were more divided, Y bacteria often in cluster states, W bacteria tended to link to a number of cells. All three displayed a remarkable algae-lysing effect on P. globosa.2. Morphological studies in the pattern of algae by using atomic force microscopy showed that algae-lysis bacteria can damage and kill P. globosa cells, and cause algal cells to rupture and intracellular materials to dissolve and finally the cells die. In the late period of algae-lysing, the algal cells were seriously damaged into free debris, and a large number of algae-lysis bacteria emerged in the co-culture. Some of these bacteria were apparently surrounded by viscous materials which may be the substances secreted by algae-lysis bacteria, which chemically dissolved algal cells.3. The different effects of algae-lysing varied in different environmental conditions. G and Y bacteria at 30‰salinity were at best algae-lysing, and worst at the 15‰, W bacteria showed the best algae-lysing at salinity 20‰, and worst at 35‰. All three algae-lysis bacteria have good algae-lysing under the conditions of total dark, light cycles and full illumination. The algae-lysing ability to P. globosa in the early growth phase was better than that in the exponential growth phase. Bacteria G had the best inhibition on effects P. globosa.4. In the late stage of algae-lysing by FCM fluorescence analysis with AO staining, it was found that P. globosa cells and algal pigment were also sharply reduced, and the co-culture system contained a large number of the corresponding algae-lysis bacteria. Physiological characteristics of the algae in the algae-lysing cycle of by FCM analysis showed that the algae-lysing trends were in steps. First P. globosa cell membrane integrity was destroyed, then chlorophyll was damaged, resulted in a non-natural death of algae at last step. In the continued action of bacteria, DNA materials of algae cells were also seriously damaged and over 90% P. globosa finally formed cell debris.5. By CLSM with PI staining or PI / AO double staining analysis in the stages of algae-lysing found that after algae-lysing the membrane of P. globosa have varying degrees of damage and deficiency in co-culture system. Also a large number of apoptosis bodies, a wide range of DNA fragmentation, DNA fragment fracture formation, and cell cavity, could be found. All these phenomena in abnormal apoptosis were formed after adding the bacteria while the control group algal cells were in good growth conditions with fluorescence negative characterization. It can be concluded that algal cells with abnormal apoptosis were closely related to the additions of bacteria. Normal physiological growth of P. globosa was induced to apoptosis by algae-lysis bacteria. Therefore the model of P. globosa's rapid apoptosis induced by algae-lysis bacteria was established.6. Experimental determination by 6-glucosidase activity could detect changes in extracellular enzyme activities. The activity changes of extracellular enzyme in the process of algae-lysisng research corroborated with the Doucette Population Dynamics Model in the water, thus it verified and complemented the dynamic of algae-lysis bacteria. The mode of action of bacteria on red tide is part of a virtuous circle. Algae-lysis bacteria, which are "drawn" from the sea, and "impact" on sea and "lose" in the sea, is natural and safe for marine native species, and also in line with treatment requirements of current international control for red tide prevention of "efficiency, low toxicity, cheap and easy".
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