Released polysaccharides (RPS) from Cyanothece sp. CCY 0110 as biosorbent for heavy metals bioremediation: interactions between metals and RPS binding sites
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Bioremediation of heavy metals using microorganisms can be advantageous compared to conventional physicochemical methods due to the use of renewable resources and efficiencies of removal particularly cations at low concentrations. In this context, cyanobacteria/cyanobacterial extracellular polymeric substances (EPS) emerge as a valid alternative due to the anionic nature and particular composition of these polymers. In this work, various culture fractions of the unicellular cyanobacterium Cyanothece sp. CCY 0110 were employed in bioremoval assays using three of the most common heavy metal pollutants in water bodies—copper, cadmium, and lead—separately or in combined systems. Our study showed that the released polysaccharides (RPS) were the most efficient fraction, removing the metal(s) by biosorption. Therefore, this polymer was subsequently used to evaluate the interactions between the metals/RPS binding sites using SEM-EDX, ICP-OES, and FTIR. Acid and basic pretreatments applied to the polymer further improve the process efficiency, and the exposure to an alkaline solution seems to alter the RPS conformation. The differences observed in the specific metal bioremoval seem to be mainly due to the RPS organic functional groups available, mainly carboxyl and hydroxyl, than to an ion exchange mechanism. Considering that Cyanothece is a highly efficient RPS-producer and that RPS can be easily separated from the culture, immobilized or confined, this polymer can be advantageous for the establishment/improvement of heavy metal removal systems.
KeywordsBioremediation Cyanobacteria Cyanothece Extracellular polymeric substances (EPS) Heavy metals Released polysaccharides (RPS)
We thank Daniela Silva from Centro de Materiais da Universidade do Porto (CEMUP), Porto, Portugal, for technical assistance with SEM-EDX. We also thank Ricardo Silva from INEB—Instituto de Engenharia Biomédica, Universidade do Porto, Porto, Portugal, for technical assistance with FTIR. The financial support was by national funds through FCT—Fundação para a Ciência e a Tecnologia/MEC—Ministério da Educação e Ciência and when applicable co-funded by FEDER funds within the partnership agreement PT2020 related with the research unit number 4293, by the project FCOMP-01-0124-FEDER-028314 (PTDC/BIA-MIC/2889/2012) and by the scholarships SFRH/BD/84914/2012 and SFRH/BDP/72400/2010.
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Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
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