Sheathless mutant of cyanobacterium Gloeothece sp. strain PCC 6909 with increased capacity to remove copper ions from aqueous solutions

ABSTRACT: The cyanobacterium Gloeothece sp. PCC 6909 and its sheathless mutant were tested for their ability to remove copper ions from aqueous solutions aiming at defining the role of the various outermost polysaccharidic investments in the removal of the metal ions. Microscopy studies and chemical analyses revealed that, although the mutant does not possess a sheath, it releases large amounts of polysaccharidic material (RPS) into the culture medium. The RPSs of the wild type and the mutant are composed by the same eleven sugars although present in different amounts, with the RPS of the mutant possessing a higher amount of acidic sugars and a lower amount of deoxysugars compared to the wild type. Unexpectedly, whole cultures of the mutant were more effective in the removal of the heavy metal in comparison with the wild type (46.3 ± 3.1 and 26.7 ± 1.5 mg of Cu2+ removed per g of dry weight, respectively). Moreover, we demonstrated that the contribution of the sheath to the metal removal capacity of the wild type is scarce, and that the RPS of the mutant is more efficient in removing copper. This suggests that the metal ions are preferably bound to the cell wall and to RPS functional groups, than to the sheath. Therefore, the increased copper binding efficiency observed for the sheathless mutant can be attributed to the release of a polysaccharide containing higher amount and/or more accessible functional groups (e.g. carboxyl and amide groups).