Physiological Characteristic Response Of Microcystis Aeruginosa To The Extracellular Substances From Aeromonas Sp. Strain FM

Serious eutrophication and frequent algae blooms in water body had been a severe environmental problem, not only in china but also throughout the world. The application of algicidal bacteria is considered as a environmentally friendly algae removal method with broad application prospects, especially, using indigenous bacteria to maintain the balance of algae biomass in aquatic ecosystems.Previously, Aeromonas sp. stain FM, was isolated from a reservoir as an algicidal bacteria. And studies have indicated that it inhibits the growth of Microcystis aeruginosa by its extracellular substances. Based on this, the chemical and physiological characteristics of M. aeruginosa were studied during the treatment by the extracellular substances from the strain FM in the present study. The main results in this study were as follows:1) The algicidal activity of strain FM was influenced by not only bacterial or algal density, but also some environmental factors. The threshold concentration of strain FM for algicidal activity on M. aeruginosa was 3.4×108 cfu·mL-1. And strain FM could effectively lyse up to 2.45×107 cells·mL-1 of M. aeruginosa. The optimum conditions for algal removal were at temperature of 25℃ with slight alkalinity and sufficient light.2)The optimum conditions for producing extracellular substances by liquid culture of strain FM was:24 h cultivation at temperature of 30℃, with pH of 8. The algicidal effects of extracellular substances produced by liquid culture and solid culture of strain FM both had significant algicidal effect, and the algicidal effect within 8 days was up to 86.0% and 84.7%, respectively.3) Strain FM released algicidal substances acting on algal cells, changed the physiological activity of the latter, decreased their intracellular proteins and enzymes, stimulated the antioxidant capacity and then enhanced membrane lipid peroxidation of the algal cells.Additionally,the algae cells secreted EPS to protect themselves from the damage.Thus, the normal physiological process of algae cells was severely affected, and eventually results in the cells death.4) The polysaccharide of M. aeruginosa was purified and prepared, also the chemical properties was preliminary analyzed. The results showed that dry weight of experimental group was higher than the control. And molecular weight of the former contents is higher than the latter. In addition, the algal polysaccharides composed of total sugar, uronic acid and sulfuric acid.5) The extracellular substances from strain FM could inhibit the release of microcystic toxins. However, with the increase of FM extracellular substances, the extracellular MCs of algae increased, and the intracellular MCs decreased. The results bear a relation to the algicidal effect of FM extracellular substances on M. aeruginosa.