Metal removal capability of two cyanobacterial species in autotrophic and mixotrophic mode of nutrition

Elham Ghorbani,Bahareh Nowruzi,Azadeh Hekmat,Masoumeh Nezhadali

doi:10.1186/s12866-022-02471-8

Abstract

BackgroundCyanobacteria are ecologically significant prokaryotes that can be found in heavy metals contaminated environments. As their photosynthetic machinery imposes high demands for metals, homeostasis of these micronutrients has been extensively considered in cyanobacteria. Recently, most studies have been focused on different habitats using microalgae leads to a 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.MethodsHere, extracellular polymeric substances (EPS) production in strains Nostoc sp. N27P72 and Nostoc sp. FB71 was isolated from different habitats and thenthe results were compared and reported.ResultCultures of both strains, supplemented separately with either glucose, sucrose, lactose, or maltose showed that production of EPS and cell dry weight were boosted by maltose supplementation. The production of EPS (9.1 ± 0.05 μg/ml) and increase in cell dry weight (1.01 ± 0.06 g/l) were comparatively high in Nostoc sp. N27P72 which was isolated from lime stones.The cultures were evaluated for their ability to remove Cu (II), Cr (III), and Ni (II) in culture media with and without maltose. The crude EPS showed metal adsorption capacity assuming the order Ni (II) > Cu (II) > Cr (III) from the metal-binding experiments.Nickel was preferentially biosorbed with a maximal uptake of 188.8 ± 0.14 mg (g cell dry wt) −1 crude EPS. We found that using maltose as a carbon source can increase the production of EPS, protein, and carbohydrates content and it could be a significant reason for the high ability of metal absorbance. FT-IR spectroscopy revealed that the treatment with Ni can change the functional groups and glycoside linkages in both strains. Results of Gas Chromatography-Mass Spectrometry (GC–MS) were used to determine the biochemical composition of Nostoc sp. N27P72, showed that strong Ni (II) removal capability could be associated with the high silicon containing heterocyclic compound and aromatic diacid compounds content.ConclusionThe results of this studyindicatede that strains Nostoc sp. N27P72 can be a good candidate for the commercial production of EPS and might be utilized in bioremediation field as an alternative to synthetic and abiotic flocculants.

Highlights

Cyanobacteria are an extremely diverse groups of prokaryotes whose adaptive capacity along with the ability to tolerate extreme conditions makes them ubiquitous in aquatic [1], and terrestrial environments [2]
As initial trials with,both strains showed that use of disaccharides as carbon source supplementation generally resulted in higher production of extracellular polymeric substances (EPS) than the use of monosaccharides (Glucose), the amounts of the total produced EPSs, cell dry weight, and residual sugar content were higher in Nostoc sp
Despite large number of studies claimed this role, only a few of them directly investigated the modification of metal removal capability by cyanobacteria under mixotrophic conditions

Summary

Introduction

Cyanobacteria are an extremely diverse groups of prokaryotes whose adaptive capacity along with the ability to tolerate extreme conditions makes them ubiquitous in aquatic [1], and terrestrial environments [2] They are well known as producers of a wide range of natural compounds which are in turn recognized as toxins that can be potential and useful in pharmaceutical industry [3,4,5,6,7,8,9,10] Genus Nostoc is a large and morphologically diverse group of phototrophic cyanobacteria which has found in various habitats. Most studies have been focused on different habitats using microalgae leads to a 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

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