Metabolism And Biological Effects Of Arsenic In Microcystis Aeruginosa

The frequent outbreaks of algal blooms causes by eutrophication and arsenicpollution have become a serious global ecology and water environment problem. Theimportance of temperature, light intensity, pH, N&P in algal blooms has beensufficient understanded, but there is still no system research about effects of As onalgal blooms. Depth understanding about effects of various environmental factors onalgal blooms has great significant to algal blooms prevention and control. In thispaper, we studied effects of As(V) stand-alone, P coexist, As(III) and As(V) ongrowth and physiology of Microcystis aeruginosa.When phosphate was deprived,100ppb As(V) has no significant effect on growthof Microcystis aeruginosa. With the increase of As(V) content, growth was inhibited,the photosynthetic rate showed a decreasing trend, CAT activity, SOD activity andMTL content all present “inverted U type”, but the content of carotenoid and SODactivity increased, which indicate As(V) inhibiting Microcystis aeruginosa growth byinhibiting photosynthesis and increasing the content of oxygen free radicals. Theincrease of CAT activity, SOD activity, MTL content and carotenoid content may bea kind of self-protection mechanism.When phosphate was rich, Microcystis aeruginosa could still keep growing underhigh As(V) content, and phosphorus can contribute to the intracellular As (III)conversion and efflux and enhance the cell tolerance of As(V). Low content of As(V)can promote the growth of Microcystis aeruginosa, increase Chl.a, carotenoids andmicrocystin content. Under the same content of As(V), Microcystis aeruginosa in thephosphate medium compared to the As(V) containing medium has higherphotosynthetic rate and microcystin production. As(V) absorption test also showedthat, under the conditions of the phosphate, the absorbed As(V) half-saturationconstant (Ks) increased, indicating phosphate can inhibit Microcystis aeruginosaabsorption of As(V), and negative correlation between As(V) absorption andphosphorus content in medium.The tolerance threshold of As(III) to Microcystis aeruginosa is between100ppband1ppm. When the threshold was exceeded, As(III) caused decline of cell biomass,Chl.a and carotenoids. Phosphate does not promote or inhibit the uptake and accumulation of As(III). The toxicity of dimethylarsinic acid (DMA) on Microcystisaeruginosa is lower than that of As(III). High content DMA dampend the growth ofMicrocystis aeruginosa, mainly because the DMA converted to other forms Asthrough the biotic and abiotic effects in the medium. DMA as the detoxification formof As conversion in Microcystis aeruginosa, the toxicity ot Microcystis aeruginosa islittle or even none.In summary, different As speciations wil have different effects on growth andphysiological of Microcystis aeruginosa, such as changes of biomass, Chl.a,carotenoids, and enzyme activity. As(III) has the strongest toxicity to Microcystisaeruginosa.