The Effect Of Environmental Factors On Microcystins Production Of Microcystis Aeruginosa And The Decrease Of Microcystins By Lemna Minor

The serious eutrophication of water body results in frequent breaking out of cyanobacterial blooms, and some genera of cyanobacteria can produce microcystins, which can cause health problems in animals and humans. The effect of microcystins on society, economy and environment has become one of the problems people concerned mostly, as well as the key in the control of cyanobacterial blooms.The environmental factors such as ammonium, phosphate, ferrite, illumination and temperature were studied to determine their effect on the growth and microcystins accumulation and release of Microcystis aeruginosa, and the decrease of microcystins by Lemna minor was also studied.The results indicate that: Microcystis aeruginosa grew well on the condition thatthe ammonium was 1.83-18.3mg.L-1 ,phosphate was less than 0.56 mg-L-1 and temperature was 35℃, .The intracellular content of microcystin-LR (MC-LR) ,toxicity of total microcystins and the amount of microcystins released into the culture medium all increased with culture time,yet the ratio of MC-RR to MC-LR were different.The result suggests that the released amount of microcystin may be regulated by environmental factors. When the concentration of ammonium was 1.83mg.L-1 ,phosphate was less than 0.56 mg.L-1, ferrite was more than 0.69 mg.L-1 and temperature was 20-25℃,much more microcystins were produced by Microcystis aeruginosa.lt demonstrats that the environmental factors favored the growth of Microcystis aeruginosa are not always suit for the production of microcystins. So we infer that the product of microcystin is a response to the stress: when the environmental factors such as temperature and nutriment are less favored the growth of Microcystis aeruginosa, microcystins were synthesized and released more, considering their toxicity to the other hydrobiology, this reaction mechanism may help to maintain the dominance of Microcystis aeruginosa in the water body.In addition,we found that Lemna minor can stand the microcystins when the concentration was as high as 960μg.L-1 ,and we also found out that Lemna minor can increase its growth rate to alleviate the damage of microcystins. In the same time, it can decrease the amount of microcystins in the culture medium, which decreased nearly 20% in 48 hours. The results above may help to explain the phenomenon that Lemna minor dominated in the pond when the microcystins were released after the decay of Microcystis blooms and it also suggest that Lemna minor can be applied in the control of cyanobacterial blooms.