Screening And Physiological Characters Of Green Algae Capable Of Inhibiting Cyanobacterium Microcystis Aeruginosa

Cyanobacterial harmful algal blooms are a global environmental problem.Microcystis,one of the most pervasive bloom forming cyanobacteria in freshwater ecosystems,its huge biomass and cyanobacterial toxins directly or indirectly threaten water ecosystem function and human health.Therefore,it is very important to control Microcystis blooms to protect the ecological environment of water bodies and reduce the risk to human health.Among the countermeasures proposed to control harmful algae blooms,biological control of harmful algae blooms presents a possible solution to inhibit the growth and reproduction of algae based on ecological balance principles.Recent research has found that the use of interspecies relationship between beneficial algae and harmful algae can inhibit the growth of harmful algae.In this study,we screened potential algae strains from preserved green algae and newly isolated green algae to control microcystis through interspecific competition based on allelopathy and exploitation competition for resources.Then we investigated their physiological characteristics,ability of inhibiting and competing with microcystis.The main results are as follows:（1）Scenedesmus sp.FACHB-1229 and Desmodesmus sp.GQ-5 were screened because of their high inhibitory effect on Microcystis aeruginosa.Scenedesmus sp.FACHB-1229 was selected from 34 strains of green algae（including Scenedesmus,Chlorella,Pediastrum,Staurastrum,Ulothrix and Monoraphidium）in Freshwater Algae Culture Collection at the Institute of Hydrobiology,among which its allelochemicals owe the highest effect of inhibiting algae.Five strains of Desmodesmu were isolated and purified from field environmental conditions.Further investigation of the inhibition effect revealed that Desmodesmus sp.GQ-5had the highest inhibition rate（IR=57.96%）against Microcystis aeruginosa FACHB-3550 among the five algae strains.（2）The result of allelochemicals and physiological characteristics for the screened algae strains are as follows:We analysed inhibiting substances of Scenedesmus sp.FACHB-1229 and Desmodesmus sp.GQ-5 by GC-MS,and result indicated that 1,2-Benzenedicarboxylic acid,bis（2-methoxyethyl）ester and 1,2-Benzenedicarboxylic acid,butyl 2-ethylhexyl ester might be the allelochemical substances.In addition,Scenedesmus sp.FACHB-1229 had the highest photosynthetic oxygen evolution rates of 229.91±10.49μmol O₂/（mg Chl.a?h）.And the ammonia nitrogen tolerance of Scenedesmus sp.FACHB-1229 was significantly higher than other strains,whose growth rate was 0.30±0.08/d when the ammonia nitrogen concentration reached up to 635.42 mg/L.（3）Preliminary investigation of interspecific competition between Microcystis and Chlorella with high growth rate was conducted.Chlorella sp.FACHB-1580（μ=0.44±0.07/d）and FACHB-1552（μ=0.38±0.05/d）with high specific growth rate.Chlorella sp.FACHB-1580also has the highest photosynthetic oxygen release rate of 198.87μmol O₂/（mg Chl.a?h）.A preliminary investigation of interspecific competition was conducted for the screened green algae.The results of co-culture in the 24-well plate showed that Chlorella sp.FACHB-1552 and FACHB-1580 could inhibit the growth of Microcystis aeruginosa under co-culture conditions.Among them,the percentage of Chlorella sp.FACHB-1552 increased from 53.37%to 99.14%when co-cultured with FACHB-3550.In the co-culture experiment of large system,the inhibition（β）of Microcystis aeruginosa to Chlorella sp.was greater than the effect（α）of Chlorella sp.to Microcystis aeruginosa,and the Microcystis aeruginosa had the competitive advantage.In summary,the spent medium of Scenedesmus sp.FACHB-1229 and Desmodesmus sp.GQ-5 had the highest ability to inhibit the growth of Microcystis aeruginosa.Scenedesmus sp.FACHB-1229 has high tolerance of ammonia nitrogen concentration and photosynthetic oxygen release rate,and is expected to be the potential material for biological control of Microcystis aeruginosa blooms by interference competition.Chlorella sp.FACHB-1552 and Chlorella sp.FACHB-1580 have high growth rate and high photosynthetic oxygen release rate,and are expected to be excellent strains for inhibiting the growth of Microcystis aeruginosa through exploitation competition.In aquaculture,there are numerous applications of adding single-celled green algae or enhancing the growth efficiency of original green algal in the water column to improve water quality or/and suppress cyanobacterial blooms.But there is still a lack of systematic and effective methods and scientific evaluation of application efficiency.In view of this,this study provides a method for screening and evaluating green algae with growth inhibition,and is expected to be scaled up to field water bodies for validation,it also provides new technical approaches for biological/ecological control and water quality improvement.