Study On The Proliferation Regulation Of Bacillus Spp.Fermentation Broth Combined With Coagulant On Gymnodinium Catenatum

Gymnodinium catenatum is a toxic red-tide alga,which can deposit in the sediment through sexual reproduction to provide the provenance for the periodic outbreak of red tide,and is a potential threat to the marine environment.In this study,the distribution and abundance of G.catenatum cysts in Fujian coastal sediments were analyzed and explore their potential for blooms.The flocculation effect of four coagulants was compared,bacillus fermentation broth and coagulant were combined to reduce the vegetative cells of G.catenatum,inhibit the cysts germination in the sediment,and control the outbreak of G.catenatum.In the sediment samples collected in the spring and summer of 2019 in Fujian sea area,the abundance of dinoflagellate cysts is between 48.9?744.7 cysts/g DW in spring and 109.4?264.4 cysts/g DW in summer.The abundance of G.catenatum cysts ranged from 0?23.7 cysts/g DW in spring and from 0?12.7 cysts/g DW in summer.Compared with the same site,the average abundance of G.catenatum cysts in summer sediment was lower than that in spring.In Ningde,Pingtan,Putian,Quanzhou and Xiamen sections,the abundance of the sections in Putian and Quanzhou is high.During the outbreak of G.catenatum red tide in 2017,high abundance of G.catenatum was detected in both places.In order to explore the removal effects of different algal inhibition methods on G.catenatum algae,coagulants and bacterial fermentation broth were used in this study to remove algae respectively.In this paper,the removal effects of four coagulants,PAC,Al₂(SO₄)₃,Fe₂(SO₄)₃ and Fe Cl₃,were compared.Through the study of algae cells,turbidity,organic matter,floc micromorphology and cells density rebound,it was found that the removal effect of polyaluminum chloride was the best.Using Zeta potentiometer,it was found that it mainly acted on algal cells by various mechanisms such as adsorption neutralization,bridging and trapping.The results showed that the fermentation liquid of Bacillus Ba3 had a good removal effect on the vegetative cells of G.catenatum.The inhibition efficiency of 2-day fermentation liquid was higher than that of 1-day and 3-day fermentation liquid.When the dosage of 2-day bacillus fermentation liquid was 0.3%(v/v),the removal rate reached90.8%in 2 days.Under the microscope,it was found that with the increase of action time,the cells of G.catenatum gradually became transparent.Under the action of 2.0%(v/v)bacterial fermentation broth,the cell membrane ruptured within 24 hours,resulting in content overflow,and the algal cells completely lysed within 72 hours.The effect of bacterial fermentation broth on killing algae is complete,but the effect time is longer.The active substances in the fermentation broth act on the algae cells to lyse them.The four coagulants combined with the bacterial fermentation broth group had obvious inhibitory effect on G.catenatum.Through the comprehensive analysis of the removal effects of algal cells,turbidity and organic matter,it was found that after the action of the polyaluminum chloride(50mg/L)combined with the bacterial fermentation broth group(0.3%,v/v)for 3h,the algal inhibition rate was 100%,and the algal cells did not rebound.To investigate the effects of polyaluminum chloride and bacterial fermentation broth on provenance germination in sediments,this study simulated the regulation and simulation experiments of two groups of sediment provenance.One group was in situ sediments,and the cysts abundance of G.catenatum is 5 cysts/g DW(group I).The other group was added G.catenatum to the in situ sediments,and the abundance is 25 cysts/g DW(group II).The results showed that the germination effect of group II was better,after10 days,the highest density was 18.0 cells/ml,and 2.3 cells/ml in group I.In the 15 day culture period,the inhibition effect of PAC group on the germination of G.catenatum cysts in group I,was between 47.8%?53.8%;and that in group II was 16.8%?48.6%.The inhibition rate of bacterial fermentation broth and polyaluminum chloride group was more than 98%,and the effect was better than that of polyaluminum chloride group.The combination of bacillus fermentation broth and coagulant can effectively remove the nutritive cells of G.catenatum,at the same time it has a good inhibitory effect on the germination of provenance,which provides a scientific reference for the prevention and control of marine red tide.