枯草芽孢杆菌发酵液对拟柱孢藻的抑制效果及作用方式

INHIBITORY EFFECT AND MECHANISM OF BACILLUS SUBTILIS FERMENTATION BROTH ON CYLINDROSPERMOPSIS RACIBORSKII

全球气候变暖和水体富营养化导致拟柱孢藻(Cylindrospermopsis raciborskii)逐渐扩散并在大量湖泊和水库形成水华,其产生的毒素对水生态系统和人类健康构成威胁,实验系统研究了枯草芽孢杆菌发酵液在不同条件下对拟柱孢藻的剂量效应关系、抑藻机制及持续时间,并分析了处理过程中胞内有机物释放的风险。结果表明,10μL/L的枯草芽孢杆菌发酵液处理初始密度为2.26×10^(9)cells/L拟柱孢藻4d后抑制率达到90.48%,并在第5天接近100%。抑制效果受处理水体的pH和水温影响较小。低剂量的枯草芽孢杆菌发酵液(5μL/L)处理1d后拟柱孢藻的光合系统受到抑制,并使超氧化物歧化酶(SOD)活性显著增加。但2d后拟柱孢藻又能恢复生长。高浓度发酵液(10μL/L)导致拟柱孢藻在1d内光合系统的完全失活,并且裂解释放了大量有机物,这些大量释放的胞内有机物在5d内能降低至6.27 mg/L。扫描电镜(SEM)显示处理组拟柱孢藻藻丝横隔收缢收缩加剧,细胞表面出现明显褶皱和萎缩,并有大量细胞裂解残体。总体而言,采用枯草芽孢杆菌控制湖泊和水库的拟柱孢水华是一种可行的方法。

Global warming and water eutrophication have led to the increased prevalence and extent of harmful algal blooms (cyanoHABs),including the potentially toxic cyanobacterial species Cylindrospermopsis raciborskii.Bacillus subtilis,one of the most commonly reported microorganisms that could inhibit the growth of cyanobacteria among microbial agents,provides an efficient,safe,and sustainable solution for controlling blooms.Most research has found that the primary or significant mechanism by which Bacillus subtilis inhibits the growth of cyanobacteria is through the release of biologically active substances with algicidal properties.In this study,the dose-effect relationship,inhibition mechanism and lasting time of Bacillus subtilis fermentation broth were systematically studied under different conditions.We also analyzed the concentrations of dissolved organic carbon,protein,and polysaccharides after treatment to assess the risk of intracellular organic matter release.In addition,we analyzed the mechanism by which microbial agents inhibit C.raciborskii by assessing its photosynthetic activity and superoxide dismutase activity (SOD) during treatment,as well as through scanning electron microscopy.The results showed that the inhibition rate reached 90.48% with 10μL/L Bacillus subtilis fermentation broth at the 4th day when the initial concentration is 2.26×10^(9) cells/L,and it grows closely to 100% at the following day.The pH and water temperature had the minimal effects on the inhibition effect.Under the treatment of 10—50μL/L Bacillus subtilis fermentation broth,the maximum photochemical quantum yield (Fv/Fm) of C.raciborskii decreased to 0 after the first day,indicating that almost all the C.raciborskii cells lost their activity within one day.Low-dose treatment (5μL/L) inhibited the photosynthetic system of C.raciborskii and caused a sharp increase in SOD activity.but C.raciborskii was able to resume growth after 2d.The high concentration of fermentation liquid resulted in the lysis of C.raciborskii and the release a large amount of organic matter,but the amount of intracellular organic matter decreased to 6.27 mg/L within five days.Large amounts of soluble proteins and polysaccharides were also detected after treated with 10—50μL/L Bacillus subtilis fermentation broth.Scanning electron microscopy (SEM) showed increased shrinkage,significant folding and atrophy on the cell surface,as well as a large number of cell lysis residues.Overall,the study demonstrates the potential of Bacillus subtilis (mainly its extracellular substances) as a sustainable method for controlling C.raciborskii blooms in lakes and reservoirs.Particular attention should be paid to the risk of the release of intracellular substances,especially toxins,from C.raciborskii during the treatment process.Subsequent studies will focus on the risk of toxin release during the microbial agent treatment of C raciborskii blooms.