The Algicidal Characteristic Of Pseudomonas Aeruginosa And The Research Of Residual MC-LR Degradation

In recent years,harmful algae blooms occurred frequently with increasing water eutrophication,leading to Microcystis and Microcystin pollution problems throughout the world.Algal control and microcystin degradation by using microbial technology has become a research hotspot with a broad application prospect.We selected Microcystis aeruginosa,the most commom cyanobacterium,as the object of research in this paper.Pseudomonas aeruginosa,which will be used in the current research,,has been screened and isolated from the contaminated water,and good performace on algal control has been confirmed during our previous investigation.This paper aims to explore the algicidal characteristic,algicidal mechanism,and the algicidal active substances of P.aeruginosa on M.aeruginosa.After algae-lysing treatment,Pycnoporus sanguineus was used to conduct residual MC-LR degradation.The results of algae-lysing treatment indicated that P.aeruginosa has a great potential to degrade M.aeruginosa through secreting active substances.Under the optimal conditions,the algicidal efficiency of 48 h fermentation liquid of P.aeruginosa achieved 83.84% after 7 days incubation.A preliminary exploration on algicidal active substances of P.aeruginosa indicated that algicidal active substances maily existed in fermentation liquid,and it had thermostability.It was difficult to precipitate by ethanol,and was easy to been extracted by strong polarity organic solvent.It was proved that the algicidal active substances couldn't be amino acids,nucleic acids,protein or sugar..The growth and metabolism of M.aeruginosa was influenced by the fermented liquid of P.aeruginosa.Fermented liquid inhibited the reproduction of M.aeruginosa by impeding the synthesis of intracellular protein and carbohydrate of cyanobacterium,changing the membrane permeability,and disordering the ion metabolism of cyanobacterium.M.aeruginosa intracellular Na+ and Cl-increasingly released,and the uptake of K+,Ca2+,Mg2+,NO3-and SO42-also decreased.What's more,the fermented liquid of P.aeruginosa caused the alteration of intracellular antioxidant enzyme activity of M.aeruginosa.Under the stress outside,catalase(CAT)and peroxidase(POD)activity presented a trend of rise first,then decrease.The accumulation of malondialdehyde(MDA)and reactive oxygen species(ROS)aggravated membrane injury.Cell membrane damage of M.aeruginosa during algae-lysing is to be probed from the perspective of surface morphology and intracellular structure of cyanobacteria and bacterial cells through electron microscope(SEM)and transmission electron microscope(TEM)analysis.P.sanguineu had the best removal efficiency on MC-LR when pH was 6.5,and the concentration of MC-LR was 1 mg·L-1.Removal efficiency of P.sanguineus on residual extracellular MC-LR reached 71.35% after 7 d incubation.There was a certain inhibiting and toxic effect of high concentration MC-LR on the growth and the degradation effect of P.sanguineus.Adsorption played a leading role on MC-LR removal by P.sanguineus hyphae during the early stages.P.sanguineus degraded MC-LR mainly through the secretion of extracellular enzyme.There was almost no degradation of intracellular enzyme on MC-LR.