Algicidal Characteristics Of Brevunditonas Sp. And Purification Of The Algicidal Substances

In recent years,the increase of population and the rapid development of industrialization constantly threatened the water absorptive capacity,and the serious pollutant concentration is beyond the limitation of water self-purification ability,which caused the eutrophication of water bodies and the burst of algae growth,such as cyanobacteria and diatom.As reported,Microcystis aeruginosa is the main species of cyanobacterial bloom,while the main species of the diatom bloom is Synedra acus.The growth cycle of M.aeruginosa is short and its cell size is small,meanwhile,some M.aeruginosa release microcystin and odor substance,which threaten the growth of aquatic organisms and caused potential problems to security and quality of drinking water.The size of diatom cell is large,and flocculation ability is inferior,which lead to the filter clogging,increased the water treatment cost,and affected treatment effect.Biological algae removal was the main topic of the present study,which used an algicidal bacterium stock in our laboratory.The tested algae were M.aeruginosa and S.acus.The main contents and results of this study were listed as follows:(1)The strain used in this study was a previous stock of our lab.In this study,we identified the species of algicidal bacteria(Brevundimonas sp.)based on 16S rRNA gene sequence,and explored the optimal culture conditions,such as pH,temperature and culture time and so on.The optimized algicidal conditions were also researched,which aim to improve algicidal efficiency,and studied the algicidal mechanism at the same time.As the basis of this study,the growth curve of this strain was monitored.The results show that,the strain was a Brevundimonas sp.,which implemented algicidal effect by indirect way.The highest algicidal activity was achieved after culture for 36 hours,and the best culture conditions were pH at 7 and temperature at 30?.(2)We explored the algicidal mechanism of the Brevundimonas sp.on M.aeruginosa and S.acus.Firstly,we studied the effect of bacterial concentrations on algicidal activity.Secondly,we studied the physiological state of algae cells during algicidal process.Thirdly,the algal cell activity was detected by flow cytometry.The result showed that the algicidal efficiency related to bacterial concentration and treatment time,the longer treatment time and higher bacterial concentration,the stronger algicidal effect.Due to the different cellular structure,the algicidal effect was different for two species.The results showed that the algicidal effect damaged cell membranes,and caused membrane lipid peroxidation.Meanwhile,the algicidal effect destroyed the photosynthesis,and affected the photosystem of algae cells.To resist the effects of disadvantageous cellular environment,the activities of antioxidant enzymes in algal cells raised,while the algal cell activity decreased or even death as time go on,which led to the decrease of enzyme activity.The results of flow cytometry detection showed that algicidal effect induced M.aeruginosa cell apoptosis,then death.(3)Further,micro electrophoresis was used to detect the surface charge change of algal cells and provided the basis information for mechanism.The results of study on M.aeruginosa showed that,at the early stage of the algicidal treatment,the increase of extracellular substance secretion lead to rapid increase of negative content,however,as the algal cells were destroyed and cell activity was reduced,zeta potential values gradually declined.The zeta value of S.acus gradually declined with the increase of treatment time during the algicidal process.As the S.acus cells were difficult to be settled,we also explored the impact of algicidal treatment on the algal sedimentation.The sedimentation experiment showed that algicidal treatment could not only restrain the growth of S.acus,but also accelerate sedimentation.The result related the decrease of absolute value of the surface charge,which affected the stability of system.(4)In order to obtain algicidal substances for practical application,the culture medium of Brevundimonas sp.was subjected to ethanol precipitation,methanol extraction,organic solvent extraction,thin-layer chromatography,and Silica-gel column chromatography.Ultimately,the RF value of active substances was determined as 0.342.We used dialysis method to distinguish the molecular weight of the algicidal substances,and it was determined to be less than 1KD.We also used HPLC-MS to identify the active substances.Due to the limitation of separation methods and time restriction,eventually no specific purified substance was identified,however,a mixture with molecular weights of 136?278?315 and 390 was detected.The results provided basis for further research.