Modification of heavy metals toxicity by Cyanobacteria Nostoc sp. N27P72 and Nostoc sp. FB71 in Culture Conditions

Abstract

Purpose: Cyanobacteria are ecologically relevant prokaryotes that can be found in environments contaminated with heavy metals. As their photosynthetic machinery imposes high demands for metals, homeostasis of these micronutrients has been extensively considered in cyanobacteria. So far, most studies have focused on treatment of wastewaters using microalgae leads to remarkable reduction of an array of organic and inorganic nutrients, but what takes place in the extracellular environment when cells are exposed to external supplementation with heavy metals remains largely unknown. Methods: Here, extracellular polymeric substances (EPS) production in strains Nostoc sp. N27P72 and Nostoc sp. FB71 isolated from different habitats are reported and compared. Cultures of both strains, supplemented with either glucose, sucrose, lactose or maltose showed that production of EPS and cell dry weight was boosted by maltose supplementation. Result: Nostoc sp. N27P72 which was isolated from lime stones was higher, resulting in 9.1 ± 0.05 µg/ml and 1.01 ± 0.06 g/l in EPS and cell dry. The cell cultures tested for their ability to remove Cu(II), Cr(III) and Ni(II) in media culture containing the maltose and without maltose as control culture. Remarkably, we showed that although these elements can be toxic, supplementing the media culture can effectively sequester their toxic effects by increasing the production of EPSs, carbohydrates and total soluble proteins in comparison to control. The crude EPS showed metal adsorption capacity assuming the order Ni(II)> Cu(II)> Cr(III) from metal-binding experiments. Nickel was preferentially biosorbed with a maximal uptake of 188.8 ± 0.14 mg (g cell dry wt) -1 crude EPS. FT-IR spectroscopy revealed treatment with Ni made changes in the functional groups and glycoside linkages in both strains. Results of Gas Chromatography Mass Spectrometry (GC–MS) to determine the biochemical composition of Nostoc sp. N27P72 showed that strong Ni(II) removal capability is suspected to be associated with the high Cyclotrisiloxane and 1,2-Benzenedicarboxylic acid content. Conclusion: The results of these investigates specified that strains Nostoc sp. N27P72 is good candidates for the commercial production of EPS and might be utilized in bioremediation field as an alternative to synthetic and abiotic flocculants.