The continuous accumulation of heavy metals in waters bears a considerable risk to both the envir... more The continuous accumulation of heavy metals in waters bears a considerable risk to both the environment and human health. Recently, new methods to remove metals from polluted waters have emerged, for e.g. the use of extracellular polymers (EPS) produced by microorganisms. The use of EPS as an alternative to the conventional chemical/physicochemical methods presents advantages like: - rapid kinetics of metal removal, - ability to remove metallic ions in low concentrations, and - possibility to treat waters contaminated with several ions For this purpose, cyanobacteria are among the ideal candidates since they are able to produce EPS rich in uronic acids with negative charges that interact with the positive ions in solution at neutral pH. In addition, cyanobacterial EPS possesses a higher number of different monomers when compared with the EPS of other microorganisms. This particular feature increases the number of possible conformations, enhancing the possibility to obtain a polymer ...
The continuous accumulation of heavy metals in waters bears a considerable risk to both the envir... more The continuous accumulation of heavy metals in waters bears a considerable risk to both the environment and human health. The use of microbial exocellular polymeric substances (EPS), mainly of polysaccharidic nature, is a valid alternative to the conventional chemical/physicochemical methods used for the bioremediation of metal-polluted waters. This new technology presents advantages such as the use of natural and renewable resources, reduced costs, rapid kinetics of metal removal, possibility to treat waters contaminated simultaneously with different metal ions, and possibility to recover valuable metals from the biosorbent. For this purpose, cyanobacteria are among the ideal candidates since their EPS are rich in negatively charged uronic acids and sulphate groups, thus having more affinity towards metal cations. They also contain a higher number of different monomers than other bacterial EPS, enhancing the possibility to obtain a polymer suitable for the treatment of a specific e...
Cyanobacterial extracellular polymeric substances (EPS) are mainly composed of high-molecular-mas... more Cyanobacterial extracellular polymeric substances (EPS) are mainly composed of high-molecular-mass heteropolysaccharides, with variable composition and roles according to the microorganism and the environmental conditions. The number of constituents – both saccharidic and nonsaccharidic – and the complexity of structures give rise to speculations on how intricate their biosynthetic pathways could be, and how many genes may be involved in their production. However, little is known regarding the cyanobacterial EPS biosynthetic pathways and regulating factors. This review organizes available information on cyanobacterial EPS, including their composition, function and factors affecting their synthesis, and from the in silico analysis of available cyanobacterial genome sequences, proposes a putative mechanism for their biosynthesis.
Many cyanobacteria produce extracellular polymeric substances (EPS) mainly of polysaccharidic nat... more 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.
Many cyanobacteria produce extracellular polymeric substances (EPS), mainly of polysaccharidic na... more Many cyanobacteria produce extracellular polymeric substances (EPS), mainly of polysaccharidic nature, which can remain associated to the cell surface as sheaths, capsules or slimes, or be released into the surrounding environment (RPS - released polysaccharides). The ability of EPS-producing cyanobacteria to remove heavy metals from solutions has been widely reported, focusing mainly on its biotechnological potential. However, the knowledge on the effects of the metals in the cell’s survival/growth is still scarce (Pereira et al., 2009; FEMS Microbiol Rev 33: 917-941). Gloeothece sp. PCC 6909 is a unicellular cyanobacterium possessing a well defined sheath surrounding its cells. A sheathless mutant of this strain (obtained by chemical mutagenesis) is also available. Although lacking the sheath, the mutant releases large amounts of RPS to the culture medium. A previous study revealed that the mutant is more effective in Cu2+ removal than the wild type due to the presence of a larger...
Phototrophic biofilms seem to be suitable candidates for tertiary wastewater treatment due to the... more Phototrophic biofilms seem to be suitable candidates for tertiary wastewater treatment due to their high uptake capacity for nutrients and other pollutants, also taking into account the time and cost savings derived from easy procedures for biomass harvesting. Biomass accrual, structure, and physiology of biofilms affect the efficiency of nutrient removal by its microbial community. Here, we construct a biofilm consisting of a cyanobacterium Synechocystis sp. and the green alga Chlorococcum sp. and determine the effect of combined variations of irradiance and temperature on the biofilm structure and function. The two species were isolated from phototrophic biofilms naturally developing in an Italian wastewater treatment plant and grown in a microcosm designed for biofilm investigations. Phototrophic biomass accumulation, percent species composition, photosynthetic response and the amount and composition of capsular polysaccharides (CPS), including anionic residues, are reported. The...
The continuous accumulation of heavy metals in waters bears a considerable risk to both the envir... more The continuous accumulation of heavy metals in waters bears a considerable risk to both the environment and human health. Recently, new methods to remove metals from polluted waters have emerged, for e.g. the use of extracellular polymers (EPS) produced by microorganisms. The use of EPS as an alternative to the conventional chemical/physicochemical methods presents advantages like: - rapid kinetics of metal removal, - ability to remove metallic ions in low concentrations, and - possibility to treat waters contaminated with several ions For this purpose, cyanobacteria are among the ideal candidates since they are able to produce EPS rich in uronic acids with negative charges that interact with the positive ions in solution at neutral pH. In addition, cyanobacterial EPS possesses a higher number of different monomers when compared with the EPS of other microorganisms. This particular feature increases the number of possible conformations, enhancing the possibility to obtain a polymer ...
The continuous accumulation of heavy metals in waters bears a considerable risk to both the envir... more The continuous accumulation of heavy metals in waters bears a considerable risk to both the environment and human health. The use of microbial exocellular polymeric substances (EPS), mainly of polysaccharidic nature, is a valid alternative to the conventional chemical/physicochemical methods used for the bioremediation of metal-polluted waters. This new technology presents advantages such as the use of natural and renewable resources, reduced costs, rapid kinetics of metal removal, possibility to treat waters contaminated simultaneously with different metal ions, and possibility to recover valuable metals from the biosorbent. For this purpose, cyanobacteria are among the ideal candidates since their EPS are rich in negatively charged uronic acids and sulphate groups, thus having more affinity towards metal cations. They also contain a higher number of different monomers than other bacterial EPS, enhancing the possibility to obtain a polymer suitable for the treatment of a specific e...
Cyanobacterial extracellular polymeric substances (EPS) are mainly composed of high-molecular-mas... more Cyanobacterial extracellular polymeric substances (EPS) are mainly composed of high-molecular-mass heteropolysaccharides, with variable composition and roles according to the microorganism and the environmental conditions. The number of constituents – both saccharidic and nonsaccharidic – and the complexity of structures give rise to speculations on how intricate their biosynthetic pathways could be, and how many genes may be involved in their production. However, little is known regarding the cyanobacterial EPS biosynthetic pathways and regulating factors. This review organizes available information on cyanobacterial EPS, including their composition, function and factors affecting their synthesis, and from the in silico analysis of available cyanobacterial genome sequences, proposes a putative mechanism for their biosynthesis.
Many cyanobacteria produce extracellular polymeric substances (EPS) mainly of polysaccharidic nat... more 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.
Many cyanobacteria produce extracellular polymeric substances (EPS), mainly of polysaccharidic na... more Many cyanobacteria produce extracellular polymeric substances (EPS), mainly of polysaccharidic nature, which can remain associated to the cell surface as sheaths, capsules or slimes, or be released into the surrounding environment (RPS - released polysaccharides). The ability of EPS-producing cyanobacteria to remove heavy metals from solutions has been widely reported, focusing mainly on its biotechnological potential. However, the knowledge on the effects of the metals in the cell’s survival/growth is still scarce (Pereira et al., 2009; FEMS Microbiol Rev 33: 917-941). Gloeothece sp. PCC 6909 is a unicellular cyanobacterium possessing a well defined sheath surrounding its cells. A sheathless mutant of this strain (obtained by chemical mutagenesis) is also available. Although lacking the sheath, the mutant releases large amounts of RPS to the culture medium. A previous study revealed that the mutant is more effective in Cu2+ removal than the wild type due to the presence of a larger...
Phototrophic biofilms seem to be suitable candidates for tertiary wastewater treatment due to the... more Phototrophic biofilms seem to be suitable candidates for tertiary wastewater treatment due to their high uptake capacity for nutrients and other pollutants, also taking into account the time and cost savings derived from easy procedures for biomass harvesting. Biomass accrual, structure, and physiology of biofilms affect the efficiency of nutrient removal by its microbial community. Here, we construct a biofilm consisting of a cyanobacterium Synechocystis sp. and the green alga Chlorococcum sp. and determine the effect of combined variations of irradiance and temperature on the biofilm structure and function. The two species were isolated from phototrophic biofilms naturally developing in an Italian wastewater treatment plant and grown in a microcosm designed for biofilm investigations. Phototrophic biomass accumulation, percent species composition, photosynthetic response and the amount and composition of capsular polysaccharides (CPS), including anionic residues, are reported. The...
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Papers by Ernesto Micheletti