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      Using extracellular polymeric substances (EPS)-producing cyanobacteria for the bioremediation of heavy metals: do cations compete for the EPS functional groups and also accumulate inside the cell?

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      Microbiology

      Microbiology Society

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          Abstract

          Many cyanobacteria produce extracellular polymeric substances (EPS) mainly of polysaccharidic nature. These EPS can remain associated to the cell surface as sheaths, capsules and/or slimes, or be liberated into the surrounding environment as released polysaccharides (RPS). The ability of EPS-producing cyanobacteria to remove heavy metals from aqueous solutions has been widely reported in the literature, focusing mainly on the biotechnological potential. However, the knowledge of the effects of the metals in the cell's survival/growth is still scarce, particularly when they are simultaneously exposed to more than one metal. This work evaluated the effects of different concentrations of Cu(2+) and/or Pb(2+) in the growth/survival of Gloeothece sp. PCC 6909 and its sheathless mutant Gloeothece sp. CCY 9612. The results obtained clearly showed that both phenotypes are more severely affected by Cu(2+) than Pb(2+), and that the mutant is more sensitive to the former metal than the wild-type. Evident ultrastructural changes were also observed in the wild-type and mutant cells exposed to high levels (10 mg l(-1)) of Cu(2+). Moreover, in bi-metal systems, Pb(2+) was preferentially removed compared with Cu(2+), being the RPS of the mutant that is the most efficient polysaccharide fraction in metal removal. In these systems, the simultaneous presence of Cu(2+) and Pb(2+) caused a mutual inhibition in the adsorption of each metal.

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          Microbial heavy-metal resistance.

          We are just beginning to understand the metabolism of heavy metals and to use their metabolic functions in biotechnology, although heavy metals comprise the major part of the elements in the periodic table. Because they can form complex compounds, some heavy metal ions are essential trace elements, but, essential or not, most heavy metals are toxic at higher concentrations. This review describes the workings of known metal-resistance systems in microorganisms. After an account of the basic principles of homoeostasis for all heavy-metal ions, the transport of the 17 most important (heavy metal) elements is compared.
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            Hard and soft acids and bases, HSAB, part 1: Fundamental principles

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              The replacement of the nondescript term ‘heavy metals’ by a biologically and chemically significant classification of metal ions

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                Author and article information

                Journal
                Microbiology
                Microbiology
                Microbiology Society
                1350-0872
                1465-2080
                February 08 2011
                February 01 2011
                October 21 2010
                February 01 2011
                : 157
                : 2
                : 451-458
                Article
                10.1099/mic.0.041038-0
                20966085
                © 2011

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