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Microcystis blooms are an environmental and ecological concern that has received a serious attention. Hydrogen peroxide (H2O2) is an environment-friendly cyanocide that is commonly used to control Microcystis blooms. While the ecological safety of H2O2 has been previously studied, its influence on bacterioplankton has not been investigated to date. In this study, we used mesocosm experiments to determine the influence of H2O2 on the dynamic changes of the community structure of bacterioplankton. By using deep-sequencing and metagenomics strategy we determined the community structures of phytoplankton and bacterioplankton assemblages that were dominated by Microcystis at a highly eutrophic Dianchi Lake, China. The results showed that Microcystis was more sensitive to H2O2 than other eukaryotic algae. More interestingly, application of H2O2 changed the community structure of bacterioplankton, evidenced by the emergence of Firmicutes as the dominant species in place of Bacteroidetes and Proteobacteria. The H2O2 treatment resulted in the community of bacterioplankton that was primarily dominated by Exiguobacterium and Planomicrobium. Our results show that the abundance changed and the bacterioplankton diversity did not recover even after the concentration of H2O2 reached to the background level. Thus, the response of bacterioplankton must be considered when assessing the ecological risks of using H2O2 to control Microcystis blooms, because bacterioplankton is the key player that forms the basis of food web of aquatic environment. [ABSTRACT FROM AUTHOR]

Microcystins (MCs) are cyclic hepatotoxic peptides produced by the bloom-forming cyanobacterium Microcystis and present a public health hazard to humans and livestock. The removal of MCs from contaminated water with powdered activated carbon (PAC) has been employed as a simple and economic treatment strategy. In this study, PAC-Fe(III) was prepared and utilized for the fast and efficient removal of MCs from water. PAC-Fe(III) exhibited superior microcystin-LR (MC-LR) removal capacity and efficiency compared to the unmodified PAC. The MC-LR removal efficiency of PAC-Fe(III) increased with decreasing pH within the pH range of 4.3 to 9.6. PAC-Fe(III) could be reused for 3 times by methanol elution while the MC-LR removal efficiency was still over 70 percent. The removal efficiency was positively correlated to the ionic strength of water and negatively correlated to alkalinity. Natural organic matter (NOM) such as humic acid (HA) and salicylic acid (SA) generated low interference with MC-LR adsorption by PAC-Fe(III). The complexation reaction between Fe3+ in PAC-Fe(III) and the functional groups of MCLR was suggested as the key mechanism of MC-LR removal by PAC-Fe(III). The results suggest that Femodified PAC is a promising material for the treatment of MC-contaminated waters. [ABSTRACT FROM AUTHOR]

Harmful cyanobacterial blooms, especially Microcystis blooms, occur worldwide and draw widespread attention. The dynamics of microcystin-producing Microcystis and competition between microcystin-producing Microcystis and non-microcystin-producing Microcystis are key to predicting and treating Microcystis blooms. Multiplex qPCR is a useful tool to assess such issues. In this study, we developed multiplex qPCR methods with newly-designed probes and primers for the microcystin-synthesis related genes mcyA and mcyE. We used seven toxic Microcystis strains and four non-toxic Microcystis strains to compare the differences in the ratios of toxic and non-toxic Microcystis in mixed cultures, which were calculated using abundances of the genes mcyA, mcyB, mcyD, mcyE and phycocyanin (PC). We also compared traditional cell counting and multiplex qPCR. Hierarchical clustering and principal component analysis indicated that mcyD was the most suitable mcy gene for quantification in laboratory experiments. mcyB abundances were always higher; we suggest that the amount of toxic Microcystis measured using mcyB might overestimate the actual percentages. [ABSTRACT FROM AUTHOR]