Study On Algicidal Efficiency And Mechanisms Of Ensifer Adhaerens And Its Algicidal Substances

In order to explore the algicidal efficiency and mechanism of algae-lysing bacteria and its active algicidal substances,the algicidal bacteria Ensifer adhaerens(r23)and Microcystis aeruginosa were studied.The r23 is an algicidal bacterium screened from the Microcystis bloom water.Based on the study of growth and algae-lysis characteristics of r23,the effects of r23 dosages and dosing modes on the release of microcystin-LR(MC-LR)and dissolved organic matter(DOM)were investigated.The changes of intra-and extra-cellular DOM(IDOM,EDOM)were analyzed by parallel factor analysis(PARAFAC).The characteristics of extracellular algicidal active substances of r23 and Brevundimonas diminuta(AA06)were compared and enriched effectively.The effects of algicidal substances on the production and release of MC-LR and DOM during algae lysis and the mechanism of algae lysis were studied.The algae-lysing efficiency of algicidal bacteria and its active substances on actual algal blooms was also studied.The algae-lysis rate of r23 was 95%even at 15℃.The supernatant of r23 culture had algae-lysis effect but not cell body,which indicates that it has indirect algae-lysing activity.The results showed that the low dosage of 2.04×106 CFU/mL not only stimulated the microalgal growth in the initial days,but also triggered the production of more toxins.The higher dosages(3.90×106,7.15×106 CFU/mL)compressed the microalgal growth and MC-LR production simultaneously.The total MC-LR of 7.15x 106 CFU/mL in double and quadripartite ways were apparently lower than the controls after 30-day treatment,but still higher than the one-off way.The PARAFAC analysis showed that tyrosine-like(C1),tryptophan-like(C2,and C3),fulvic acid-like(C4),and humic acid-like(C5)substances are common components in IDOM and EDOM,while IDOM possessed one more component of phycocyanin(C6).The Fmax of C1 and C3 in EDOM were resulted from lysing microalgae.C2 in EDOM came from nutrient broth medium,which could be consumed by r23.C4 and C5 in EDOM were mainly resulted from the growth of r23,The algicidal active substances of r23 and AA06 are chemically stable over a wide range of temperatures and pH values,and have strong polarity.It has similar infrared spectra and may contain hydroxyl or secondary amine functional groups and benzene ring,Algae-lysing active substance of r23 was selected for subsequent experiments.The high dose(6 mg/mL)of r23 algicidal substance can make algal cells agglomerate in the early stage,and can rapidly control the growth of algal cells,thus inhibiting MC-LR synthesis and reducing the release of MC-LR into water..The growth of algae cells was stimulated and more MC-LR was produced in the early stage of treatment with low dose(3,1.5 mg/mL),but the growth of algae cells was completely inhibited after 15 days.The dose of 6 mg/mL algicidal substances can directly damage cell antioxidant system and lead to algal death.The dose of 3 mg/mL increased the level of algal oxidative damage and stimulate the activities of antioxidant system enzymes(catalase,CAT;total superoxide dismutase,T-SOD)or non-enzymatic(reduced glutathione,GSH)in a short time,but algae cells eventually died as algae lysis proceeded.In the 1.5 mg/mL dosage treated group,the oxidative damage level and GSH activity of algae cells increased,but the activities of T-SOD and CAT in the antioxidant system were not significantly stimulated.The double and quadripartite ways treatments reached the same level as the single dose on the 8th and 15th day,respectively.The decrease of GSH concentration lagged behind that of T-SOD and CAT,which was related to the combination of GSH and MC-LR for detoxification.The chla level in water can be effectively controlled by r23 and AA06 algae-lysing bacterial culture and algaicidal active substances.On the fourth day,the algal culture turns yellow and the algal cells shrink and break up.The total MC-LR concentration decreased by 44.3-60.4%after 7 days of algae lysis compared with the control,but the remaining algae toxins and degradation products of algae toxins would bring ecological risks.