Study On The Inhibitory Effect Of Immobilized Algicidal Bacteria Against Microcystis Aeruginosa

Research on inhibiting algal blooms is very essential along with water eutrophication.People usually take physical,chemical and biological measures to controll algal bloom.Even if physical and chemical methods own powerful algal inhibition effects during short time,the treatment cost is much higher,and these methods often result in water second pollution.Up to date,biological method including algicidal bacteria is attracting more and more attention.Thus,algicidal bacteria are extensively applied in algal b ooms control.Application of algicidal bacteria is a potential bio-technique to inhibit harmful algal growth and remove algal blooms.At present,algicidal bacteria are mainly used in the form of freely suspended cells.In this study,the bacterium Brevundimonas sp.AA06 against Microcystis aeruginosa was isolated from soil and the algicidal effects of immobilized strain AA06 were investigated.Polyvinyl alcohol(PVA)and sodium alginate(SA)were selected as carriers to immobilize algicidal bacteria.The best preparation conditions of PVA-SA beads are:PVA 10%,SA 0.5%,immobilized microorganisms 2:1,linking time 24h.The spherically immobilized beads(?p=3.0-4.0 mm)were prepared by PVA and SA.Scanning electron microscopy(SEM)images of polyvinyl alcohol-sodium alginate(PVA-SA)beads showed that there were a large number of pores inside and that the bacterial cells adhered to the skeleton.Cyanobacterial dose-relationship tests showed that the EC50 value of PVA-SA beads was equivalent to 2.1 8×107 CFU/mL,which exhibited slightly stronger algicidal effects than freely suspended cells(1.37×107 CFU/mL).To compare the difference between PVA-SA beads and freely suspended cells on algal growth during long-term algicidal procedure,the exposure of M.aeruginosa was operated using a sequencing batch mode.The PVA-SA beads inhibited the growth of M.aeruginosa up to 60 days,which was much longer than freely suspended cells(34 days).The PVA-SA beads were still spherical after immersing in algae cultures for 30 days.Meanwhile,the inside of beads melted and fused together,resulting in the pore structure disappearing.The fiber skeleton appeared more fragile and tenuous after 30 days.When M.aeruginosa was exposed to PVA-SA beads at EC70,96h,the total concentrations(intra and extra cellular)of microcystin-LR(MC-LR)remained stable at 40.0±5 ?g/L,with intracellular MC-LR declining.When auaqtic plants were expoed to beads and freely suspended cells,freely suspended cells and beads both could effectively inhibit the growth of algae cells.The COD,TN,TP,NH4+-N concentration of water treated with freely suspended cells were influenced due to bacteria medium,leading to a sharp rise of COD,TN,TP,NH4+-N concentration in water,while beads had little effect on COD,TN,TP,NH4+-N concentration in water.When the aquatic plants were exposed to freely suspended cells,the activity of antioxidant enzyme including SOD,CAT and POD increased within 4 days,and the concentration of GSH and SP were also increased.The normal physiological activities of the plant cells were affected and the synthesis of protein was inhibited,resulting in the decrease of the activity of SOD,CAT,POD and concentration of GSH and SP.In comparison,when aquatic plants were exposed to beads,beads had little effect on aquatic plants,and did not significantly affect the normal physiological functions of plants.