Effects Of Lysine On Photosynthesis And The Microcystin Production Of Microcystis Aeruginosa Under Different Light Density

A certain concentration of lysine (lys) can inhibit the growth of Microcystis aeruginosa in light conditions while no effects will happen in dark conditions. To confirm if photosynthesis II (PSII) is the point that lys inhibit the growth of Microcystis aeruginosa, this paper discusses the inhibition effects of lys of different concertrations on three different Microcystis aeruginosa (non-toxic alga FACHB469, low toxic algal strains FACHB977highly toxic algae strains FACHB905) with chlorophyll fluorescence parameters (Fv/Fm and Yield, ETR, and qP) as indicators under different light densities. Some strains of Microcystis aeruginosa cells will synthesize into microcystins(MC), mostly MC-LR. In order to further investigate whether the effect of algae produces toxin is induced by stress, this experiment tests the amount of MC-LR according to the stresses of three different Microcystis aeruginosa under different light densities and at different concertrations.The results showed that lys less than0.6mg/L with different light densities will not inhibit the cellphysiological growth of algal cells, instead, it can improve the light capture efficiency, solar energy conversion efficiency and electron transport rate of PSII systems (photosynthetic reaction center).which to some extent, promote the photosynthesis of algae.2mg/L lys has no obvious effect on the photosynthesis of algae.Lys more than5mg/L will cause stress on Microcystis aeruginosa, affecting the light capture efficiency, solar energy conversion efficiency and electron transport rate of PSII systems. More than10mg/llys, will cause severe toxicity to the algae and inhibit its physiological growth, resulting in the termination of photosynthesis. Microcystis aeruginosa of different concertrations grow slowly and die gradually under the light of10μE·m-2·s-1and120μE·m-2·s-1, whose inhibition capacity is stronger than that of40μE·m-2·s-1. For Microcystis aeruginosa of different strains, the Fv/Fm, Yield and ETR of non-toxic algae, low toxic algal strains and high toxic algae strains are469,977and905respectively, which indicates that under stress, toxic algal strains have stronger resistance than that of the non-toxic alga.More toxin will be produced with time goes longer. The amount of toxin in the5mg/l-10mg/I group is obvious higher than that of the control group. The increase rates of toxin under the lights of10μE·m-2·s-1and120μE·m-2·s-1are significantly higher than that of the40μE·m-2·s-1.According to the chlorophyll fluorescence parameters, it is found out that low toxin strain977and high toxin strain905will produce more toxin when stressed, and the latter produces much more toxin than the former. It shows that Microcystis may produce toxin for defense when the lysine is stressed.