Study On The Physiology And Ecology Of Chrysosporum Ovalisporum: A Newly Recorded Species Of Water Bloom Forming Cyanobacteria From China

The increased occurrence of harmful cyanobacterial species and,with this,higher frequency of cyanobacteria blooms,closely associated with eutrophication and climate change,have attracted increasing attention worldwide.However,the knowledge about the physiological and ecological features of these invasive cyanobacterial species is apparently deficient,especially their ecological competition strategies and physiological responses in the new colonies and settlements.In 2013 and 2014,an unidentified cyanobacterial bloom was observed in an artificial water body connected with Lake Dishui and is managed by the Shanghai branch of the China Oceanic Administration(hereafter,Donghai Pond).In this paper,we conducted a serial in situ and laboratory experiments to study the taxonomy,life cycle,allelopathic strategy,response to high nutrients addition,relationship with sympatric zooplankton community and the physiological and ecological response to the crude extract of a terrestrial plants of this unknown filamentous cyanobacterium.Our study is benefit for the knowledge accumulation of cyanobacterial biology in China and helpful for relevant government sector making water resources management policy,dealing with the crisis brought by the invade bloom-forming cyanobacteria.Details of our study are as follows:1.The unidentified cyanobacterial species from Donghai pond was collected and isolated.Four unstained and purified algal strains were obtained by above process.The morphological characteristics and cell ultrastructure were observed by using common light microscope(LM),scanning electron microscope(SEM)and transmission electron microscope(TEM).The 16 S rRNA gene were extracted and sequenced and were used to testify its biological molecular characteristics.The results confirmed that this unknown species is a newly recorded species of water bloom forming Cyanobacteria from China——Chrysosporum ovalisporum(Cyanophyta).In addition,it also was found that this geographical populations could produce Cylindrospermopsin(CYN)by sequencing the cyr gene cluster and testing the its cell-free filtrate by using liquid chromatography mass spectrometry(LC-MS).2.The field observation and laboratory culture experiments indicated that water temperature(WT)is the key factor influencing the dynamic of C.ovalisporum in Donghai Pond,but not the nutrient.Field data showed that C.ovalisporum appeared in the water column at 20 ? in early summer,and then propagated via hormogon.Only few percentage cells(<0.5%)differentiated into akinete when WT between 27 to 32 ?.When WT below 27 ?,the akinete differentiation would be dramatically induced;WT between 21 to 27 ? were optical temperature range for differentiation,and 24 ? was proposed as the optical threshold.However,when WT below 15 ?,the growth of C.ovlisporum would be inhibited,and no akinete be observed on the trichome.3.The field data and laboratory experiments suggested that C.ovalisporum has a negative allelopathic effect on Microcystis panniformis growth.It also lowered the photosynthetic efficiency(Fv/Fm and rETR)and affected the enzyme system(ALP and SOD)of M.panniformis.The allelopathic effect,inspired by its secondary metabolites,was recognized as its magic weapon and strategy to win the competition with other cyanobacterium in sympatric water column.However,this competitive strategy is closely related to water temperature.During summer time,high temperature is suitable for C.ovalisporum growth,when its allelopathic effect showed an infinite power.However,when autumn coming(WT<20?),its growth was limited and accordingly the allelopathic effect disappeared.4.To understand whether C.ovalisporum maintains its dominance under accelerated eutrophication or hyper-eutrophication conditions.A mesocosm experiment was conducted using 100 L bucket under natural light and temperature conditions in Lake Dishui,China.It revealed that N added or P added to lake water promoted growth of both filamentous cyanobacteria(C.ovalisporum)and single cell green algae(Coelastrum,Chlorella,Tetraedron and Scenedesmus),and the biomass of N & P treatments significantly higher than the other two treatments.However,the relevant abundance of C.ovalisporum showed a decrease trend with the increase of nutrient concentration.Single cell green algae showed an opposite tendency.At the end of the experiment,the small green algae accounted for the absolute superiority,which indicated that the small sized algae were more susceptible to competitive advantage under high nutrient conditions.We foresee that Chlorophyte(small sized green algae)dominance may could be one of possible succession pattern in hyper-eutrophication water body.5.To investigated the relationship between invasive cyanobacteria and zooplankton community,and the latter response to the former,high frequency field sampling data(weekly data)of zooplankton and environmental parameters were analyzed by using redundancy analysis(RDA)and fitting methods.The results showed that C.ovalisporum was a key factor affecting the community structure,abundance and diversity of zooplankton in Donghai Pond.To figure out the indication effect of zooplankton to the biomass variation of C.ovalisporum,the indicator species threshold analysis(TITAN)method was applied first time.The result showed that zooplankton community structure changed greatly when the C.ovalisporum biomass reached 19.37 mg L-1.Besides,it also showed that seven zooplanktons species: Daphnia carinata,Vorticella sp.,Lecane ohioensis,Tetrarhymena pyriformis,Diaphanosoma leuchtenbergianum,Polyarthra vulgaris and Copepodite could be used as an indicator species,reflecting the increased trend of C.ovalisporum in the water column.6.The allelopathic effects of extract of the terrestrial plant Wedelia Chinensis on C.ovalisporum indicated that low concentrations of extract can promote the growth of the latter,while high concentrations of extract could destroy intracellular thylakoids,carboxysomes,gas vesicle and other ultra-microstructures of C.ovalisporum and inhibit the synthesis of chlorophyll-a,phycocyanin and other photosynthetic pigments.In addition,the medium with high concentrations extract have a inhibitory effect on the efficiency of photosynthetic system ? and the growth of C.ovalisporum,causing algal cells damage and lysis.The results of nonlinear fitting analysis showed that Fv/Fm value and the extracts of W.Chinensis have significant logistic correlation.The half lethal concentration of W.Chinensis on C.ovalisporum after 24 h,48h,72 h and 144 h were 3.78,4.47,4.72 and 6.55 g L-1,respectively.