| With the aggravation of global climate warming and water eutrophication,cyanobacteria bloom events occur frequently all over the world,destroying the water environment and affecting the water ecological balance.When cyanobacteria bloom outbreaks,often accompanied by the release of algal toxins,reduce biodiversity,and seriously harm human health and survival,while reducing the utilization of water resources,and hinder economic development.Microcystis bloom is the most common,and its outbreak frequency is high,its duration is long,its distribution range is wide,and its impact is great.In recent years,the search for efficient and environmentally friendly methods to remove algae is still the hot spot and difficult point of research.With the characteristics of low cost,high efficiency,no secondary pollution,microbial algal removal technology has attracted much attention from researchers,which is the development trend of cyanobacteria bloom control technology.Bacteria are an important part of the aquatic ecosystems,and algal lytic bacteria as a new algal removal agent provides a new idea for the study of algal removal technology.In this study,Microcystis aeruginosa,the dominant algae species in algal bloom,was selected as the algal lysing object,and the algal lysing characteristics and mechanism of the algal lysing bacteria were isolated and screened from the humus of Taihu Lake,so as to provide species resources and theoretical support for algal bloom control.The main research results are as follows:1.An algolytic strain S4 was isolated from the humus of Taihu Lake,which had a high algolytic effect on Microcystis aeruginosa FACHB-905.Its colonies were milky white,indicating rough and irregular edges,and it was Gram-positive.Based on the analysis of 16S r RNA sequence and phylogenetic tree,strain S4 belonged to Bacillus.The obtained gene number of strain S4 was NMDCN00017DJ in the China Data Center for Microbiology.2.The alginolytic method of microcystic aeruginosa was indirect alginolytic.After 7 days of co-culture of Microcystic aeruginosa with the protobacterial solution,extracellular secreted solution,bacterial suspension and ultrasonic crushing solution of strain S4,the extracellular secreted solution group had the best alginolytic effect,chlorophyll a decreased to0.08±0.05mg/L,alginolytic rate was 94.41±4.2%.Among all the growth stages of strain S4,the logarithmic growth stage of algolytic bacteria S4 had the strongest algolytic effect,and the chlorophyll a content was 0.16±0.12mg/L after 7 days,which was significantly lower than that at stagnation stage and stable stage(P<0.01).Carry out gradient dilution of the original bacterial solution to 10~1-10~5 times,When the dilution ratio is 10~3,the algal solubilization rate is 91.33±3.44%,which is only 1.33%lower than the algal solubilization rate.Under different temperature,the algolytic effect was the best when the culture temperature was 30℃compared with 20℃and 25℃,and the algolytic rate was 94.74±3.93%.Photoperiod changes of soluble dissolve algae algae bacteria S4 effect had no obvious effect,microbial S4 in light conditions(12 h:12 h light and dark circle,which were)and no light(dark),all conditions,during the period of experiment content of chlorophyll a,there is no significant difference,strain S4 of dissolved substances to the patina of algal dissolved algal role does not have light dependence.When the initial concentration of chlorophyll a was lower than 1.46mg/L,the algaecolysis rate of S4 reached more than 80%in 4 days.3.Under the action of the extracellular secretory fluid of S4,the algal cells were damaged by oxidation and the integrity of algal cells was seriously damaged.The content of malondialdehyde(MDA)and the activity of catalase(CAT)increased with the continuous culture time.After 7 days,MDA content was 3.71±0.62μmol/mg pro and CAT content was80.75±8.51 U/mg pro.The activity of superoxide dismutase(SOD)and peroxidase(POD)increased in the early stage and decreased in the later stage.The SOD activity reached the highest value of 138.24±5.6 U/mg pro on the 4th day,and the POD activity reached the highest value of 118.71±22.9 U/mg pro.The extracellular substances secreted by algaeclytic bacteria S4 produced oxidative stress on algaecal cells,and with the extension of culture time,the oxidative damage degree of algaecal cell membrane was deepened,causing the response of enzyme antioxidant system and non-enzyme antioxidant system.4.Under the algaeclytic bacteria S4,the expression of photosynthetic gene psa B in algaeclytic cells was down-regulated by 0.45 times after 24h,and the relative expression of genes mcy B,mcy D and mcy A involved in the synthesis of algin toxin were down-regulated significantly after 72 h(P<0.01).Strain S4 could inhibit the photosynthesis of algal cells,affect the normal growth and metabolism of algal cells,and effectively inhibit the expression of microcystin synthesis gene. |
