Cyanobacterial exopolysaccharides: their nature and potential biotechnological applications

Engineering strategies and applications of cyanobacterial exopolysaccharides: A review on past achievements and recent perspectives

Cyanobacteria are ideally suited for developing sustainable biological products but are underdeveloped due to a lack of genetic tools. Exopolysaccharide (EPS) is one of the essential bioproducts with widespread industrial applications. Despite their unique structural characteristics associated with distinct biological and physicochemical aspects, EPS from cyanobacteria has been underexplored. However, it is expected to accelerate in the near future due to the utilization of low-cost cyanobacterial platforms and readily available information on the structural data and specific features of these biopolymers. In recent years, cyanobacterial EPSs have attracted growing scientific attention due to their simple renewability, rheological characteristics, massive production, and potential uses in several biotechnology domains. This review focuses on the most recent research on potential new EPS producers and their distinct compositions responsible for novel biological activities. Additionally, nutritional and process parameters discovered recently for enhancing EPS production and engineering strategies applied currently to control the biosynthetic pathway for enhanced EPS production are critically highlighted. The process intensification of previously developed EPS extraction and purification processes from cyanobacterial biomass is also extensively explained. Furthermore, the newly reported biotechnological applications of cyanobacterial exopolysaccharides are also discussed.

Microalgae's polysaccharides, are they potent antioxidants? Critical review

The scientific community continue to explore novel bioactive molecules by investigating natural origins; microalgae are photosynthetic organisms considered as a sustainable resource to use in many fields. They present a high diversity in species and richness in terms of attractive bio-compounds. The aim of this review is to (1) provide first an overview of current issues related to oxidative stress, and propose a natural metabolite derived from eukaryotic and prokaryotic microalgae; 'polysaccharides' as a powerful antioxidant agent, then, (2) organize the available data on the antioxidant potential of polysaccharides derived from the main microalgal groups (red microalgae, green microalgae, and cyanobacteria) and especially highlighted the key species of each group (Porphyridium sp., Chlorella sp., and Arthrospira sp., respectively), meanwhile, (3) we described the chemical composition of polysaccharides from each class, and (4) we cite briefly the most factors affecting the antioxidant activity of these molecules. Finally, we explored the major challenges and gaps found to require more investigation.

Prospects of a hot spring-originated novel cyanobacterium, Scytonema ambikapurensis, for wastewater treatment and exopolysaccharide-enriched biomass production

The present work performs the polyphasic characterization of a novel cyanobacterial species Scytonema ambikapurensis isolated from an Indian hot spring and evaluates its wastewater bioremediation potential. While the physicochemical analyses of the wastewater indicated high load of nutrients and metals, the wastewater bioremediation experiment performed using the test cyanobacterium denoted the removal of 70 and 86% phosphate, 49 and 66% sulfate, 96 and 98% nitrate, 91 and 92% nitrite, 95 and 96% ammonia, 66 and 72% chloride, 79 and 81% zinc, 68 and 80% nickel, 81 and 90% calcium, and 80 and 90% potassium from the autoclaved and un-autoclaved wastewater, respectively, after 20 days of culturing. The kinetics study of zinc and nickel removal from wastewater revealed that the cyanobacterium employed sequential biosorption (by following pseudo-second-order kinetics model) and bioaccumulation methods to remove these two metals. The quality of the autoclaved and un-autoclaved wastewater was further improved by the cyanobacterium through reduction of hardness by 74 and 81%, respectively. In wastewater, the cyanobacterium not only enhanced its biomass, chlorophyll and carbohydrate contents, but also produced small amount of released and high capsular exopolysaccharide (EPS). The FTIR and TGA analyses of capsular EPS unraveled that it was a negatively charged sulfated biomolecule having thermostability up to 240 °C, which suggested its possible use as excellent emulsifying, viscosifying, and biosorption agent. The credibility of this EPS as biosorption agent was ascertained by evaluating its metal chelating ability. Finally, the experimental data denoting the ability of S. ambikapurensis to bioremediate wastewater and simultaneously produce EPS was statistically validated by PCA1-pollutant removal model and the PCA2-cellular constituent model, respectively. Briefly, the study discloses that the cyanobacterium has huge biotechnological and industrial importance as it bioremediates wastewater and simultaneously produces thermostable exopolysaccharide.

High resolution functional analysis and community structure of photogranules

Photogranules are spherical aggregates formed of complex phototrophic ecosystems with potential for “aeration-free” wastewater treatment. Photogranules from a sequencing batch reactor were investigated by fluorescence microscopy, 16S/18S rRNA gene amplicon sequencing, microsensors, and stable- and radioisotope incubations to determine the granules’ composition, nutrient distribution, and light, carbon, and nitrogen budgets. The photogranules were biologically and chemically stratified, with filamentous cyanobacteria arranged in discrete layers and forming a scaffold to which other organisms were attached. Oxygen, nitrate, and light gradients were also detectable. Photosynthetic activity and nitrification were both predominantly restricted to the outer 500 µm, but while photosynthesis was relatively insensitive to the oxygen and nutrient (ammonium, phosphate, acetate) concentrations tested, nitrification was highly sensitive. Oxygen was cycled internally, with oxygen produced through photosynthesis rapidly consumed by aerobic respiration and nitrification. Oxygen production and consumption were well balanced. Similarly, nitrogen was cycled through paired nitrification and denitrification, and carbon was exchanged through photosynthesis and respiration. Our findings highlight that photogranules are complete, complex ecosystems with multiple linked nutrient cycles and will aid engineering decisions in photogranular wastewater treatment.

First characterization of cultivable extremophile Chroococcidiopsis isolates from a solar panel

Introduction

Microorganisms colonize a wide range of natural and artificial environments. Even though most of them are unculturable in laboratory conditions, some ecosystems are ideal niches for bioprospecting extremophiles with unique properties. Up today, there are few reports concerning microbial communities found on solar panels, a widespread, artificial, extreme habitat. Microorganisms found in this habitat belong to drought-, heat- and radiation-adapted genera, including fungi, bacteria, and cyanobacteria.

Methods

Here we isolated and identified several cyanobacteria from a solar panel. Then, some strains isolated were characterizated for their resistance to desiccation, UV-C exposition, and their growth on a range of temperature, pH, NaCl concentration or diverse carbon and nitrogen sources. Finally, gene transfer to these isolates was evaluated using several SEVA plasmids with different replicons to assess their potential in biotechnological applications.

Results and discussion

This study presents the first identification and characterization of cultivable extremophile cyanobacteria from a solar panel in Valencia, Spain. The isolates are members of the genera Chroococcidiopsis, Leptolyngbya, Myxacorys, and Oculatella all genera with species commonly isolated from deserts and arid regions. Four of the isolates were selected, all of them Chroococcidiopsis, and characterized. Our results showed that all Chroococcidiopsis isolates chosen were resistant up to a year of desiccation, viable after exposition to high doses of UV-C, and capable of being transformed. Our findings revealed that a solar panel is a useful ecological niche in searching for extremophilic cyanobacteria to further study the desiccation and UV-tolerance mechanisms. We conclude that these cyanobacteria can be modified and exploited as candidates for biotechnological purposes, including astrobiology applications.

Salinity-driven ecology and diversity changes of heterocytous cyanobacteria in Australian freshwater and coastal-marine microbial mats

N₂ -fixing heterocytous cyanobacteria are considered to play a minor role in sustaining coastal microbial mat communities developing under normal marine to hypersaline conditions. Here, we investigated microbial mats growing under different salinities from freshwater mats of Giblin River (Tasmania) to metahaline and hypersaline mats of Shark Bay (Western Australia). Analyses of genetic (rRNA and mRNA) and biological markers (heterocyte glycolipids) revealed an unexpectedly large diversity of heterocytous cyanobacteria in all the studied microbial mat communities. It was observed that the taxonomic distribution as well as abundance of cyanobacteria is strongly affected by salinity. Low salinity favoured the presence of heterocytous cyanobacteria in freshwater mats, while mats thriving in higher salinities mainly supported the growth unicellular and filamentous non-heterocytous genera. However, even though mRNA transcripts derived from heterocytous cyanobacteria were lower in Shark Bay (<6%) microbial mats, functional analyses revealed that these diazotrophs were transcribing a substantial proportion of the genes involved in biofilm formation and nitrogen fixation. Overall, our data reveal an unexpectedly high diversity of heterocytous cyanobacteria (e.g. Calothrix, Scytonema, Nodularia, Gloeotrichia, Stigonema, Fischerella and Chlorogloeopsis) that had yet to be described in metahaline and hypersaline microbial mats from Shark Bay and that they play a vital role in sustaining the ecosystem functioning of coastal-marine microbial mat systems.

Hydrating Capabilities of the Biopolymers Produced by the Marine Thermophilic Bacillus horneckiae SBP3 as Evaluated by ATR-FTIR Spectroscopy

The surfactin-like lipopeptide (BS-SBP3) and the exopolysaccharide (EPS-SBP3) produced by the polyextremophilic Bacillus horneckiae SBP3 (DSM 103063) have been recently described as valuable biopolymers useful in biotechnological applications. To investigate the hydrating capabilities of BS-SBP3 and EPS-SBP3, here we evaluated (i) their wetting properties, measuring the contact angle; (ii) their moisture uptake abilities using the gravimetric method; and (iii) their hydrating states (from 0 to 160% w/w of water content) using ATR-FTIR spectroscopy. BS-SBP3 reduced the water contact angle on a hydrophobic surface from 81.7° to 51.3°, whereas the contact angle in the presence of EPS-SBP3 was 72.9°, indicating that BS-SBP3 improved the wettability of the hydrophobic surface. In the moisture uptake tests, EPS-SBP3 absorbed more water than BS-SBP3, increasing its weight from 10 mg to 30.1 mg after 36 h of 100% humidity exposure. Spectral distance and cross-correlation analyses were used to evaluate the molecular changes of the two biopolymers during the hydration process. As the water concentration increased, BS-SBP3 spectra changed in intensity in the two contributions of the OH-stretching band named "closed" and "open" (3247 and 3336 cm^-1, respectively). Differently, the spectra of EPS-SBP3 exhibited a broader peak (3257 cm^-1), which shifted at higher water concentrations. As evaluated by the spectral distance and the wavelet cross-correlation analysis, the OH-stretching bands of the BS-SBP3 and EPS-SBP3 changed as a function of water content, with two different sigmoidal trends having the inflection points at 80% and 48%, respectively, indicating peculiar water-properties of each biopolymer. As wetting agents, these biopolymers might replace industrially manufactured additives in agriculture and the food and cosmetic industries.

Decay of Trichomes of Arthrospira platensis After Permeabilization Through Pulsed Electric Fields (PEFs) Causes the Release of Phycocyanin

The cyanobacterium Arthrospira platensis is a promising source of edible proteins and other highly valuable substances such as the blue pigment-protein complex phycocyanin. Pulsed electric field (PEF) technology has recently been studied as a way of permeabilizing the cell membrane, thereby enhancing the mass transfer of water-soluble cell metabolites. Unfortunately, the question of the release mechanism is not sufficiently clarified in published literature. In this study, the degree of cell permeabilization (cell disintegration index) was directly measured by means of a new method using fluorescent dye propidium iodide (PI). The method allows for conclusions to be drawn about the effects of treatment time, electric field strength, and treatment temperature. Using a self-developed algorithm for image segmentation, disintegration of trichomes was observed over a period of 3 h. This revealed a direct correlation between cell disintegration index and decay of trichomes. This decay, in turn, could be brought into a direct temporal relationship with the release of phycocyanin. For the first time, this study reveals the relationship between permeabilization and the kinetics of particle decay and phycocyanin extraction, thus contributing to a deeper understanding of the release of cell metabolites in response to PEF. The results will facilitate the design of downstream processes to produce sustainable products from Arthrospira platensis.

Spatio-Temporal Monitoring of Benthic Anatoxin-a-Producing Tychonema sp. in the River Lech, Germany

Incidents with toxic benthic cyanobacteria blooms have been increasing recently. In 2019, several dogs were poisoned in the river Lech (Germany) by the benthic anatoxin-a-producing genus Tychonema. To characterize spatial and temporal distribution of potentially toxic Tychonema in this river, a systematic monitoring was carried out in 2020, focusing on the occurrence of the genus, its toxin production and habitat requirements. Tychonema and cyanobacterial community composition in benthic mats and pelagic samples were identified using a combined approach of microscopy and DNA sequencing of the 16S rRNA gene. In addition, anatoxin-a concentrations of selected samples were measured using the ELISA method. The habitat was characterized to assess the ecological requirements and growth conditions of Tychonema. Tychonema mats and anatoxin-a were detected at several sampling sites throughout the entire study period. Toxin concentrations increased with the progression of the vegetation period and with flow direction, reaching values between 0 and 220.5 µg/L. Community composition differed among pelagic and benthic samples, with life zone and substrate condition being the most important factors. The results of this study highlight the importance of monitoring and understanding the factors determining occurrence and toxin production of both pelagic and benthic cyanobacteria due to their relevance for the health of humans and aquatic ecosystems.

Influence of Process Operation on the Production of Exopolysaccharides in Arthrospira platensis and Chlamydomonas asymmetrica

Extracellular polysaccharides, or exopolysaccharides are high–molecular weight sugar-based polymers expressed and secreted by many microorganisms. As host organisms, the functions of exopolysaccharides are diverse, ranging from physical protection via biofilm formation, adhesion, and water retention to biological functions that are not entirely understood such as viral attachment inhibition. Industrial applications of exopolysaccharides can be found in food texture modification; for example, utilizing the hydrocolloidal properties of exopolysaccharides for thickening and gelling purposes to improve food quality and texture. Over the last decade, biologically active exopolysaccharides produced by microalgae have received attention for their potential as antiviral, antibacterial and antioxidative compounds and in the applications. However, relatively low yield and productivity are the limiting factors for full-scale industrial application. In this study, the well-known prokaryotic phototrophic microorganism Arthrospira platensis and the comparatively unknown eukaryotic unicellular green alga Chlamydomonas asymmetrica were used to evaluate the influence of different process parameters on exopolysaccharides formation and productivity. In addition to the essential control variables (light and temperature), the influence of operational techniques (batch and turbidostat) were also investigated. Although the two studied algae are differently affected by above parameters. The light intensity was the most influential parameter observed in the study, leading to differences in exopolysaccharides concentrations by a factor of 10, with the highest measured concentration for A. platensis of cEPS = 0.138 g L−1 at 180 μmol m−2 s−1 and for C. asymmetrica of cEPS = 1.2 g L−1 at 1,429 μmol m−2 s−1. In continuous systems, the achieved exopolysaccharides concentrations were low compared to batch process, however, slightly higher productivities were reached. Regardless of all screened process parameters, C. asymmetrica is the better organism in terms of exopolysaccharides concentrations and productivity.

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

Background

Cyanobacteria 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.

Methods

Here, 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.

Result

Cultures 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.

Conclusion

The 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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02471-8.

Mixotrophic conditions can be used to optimize the biosorption controllable factors for the maximum metal removal efficiency.

Different habitats (lime stones of Khuzestan province and fresh water of of Golestan province) can effect the uptake of heavy metal by two Nostoc species (Nostoc sp. N27P72 and Nostoc sp. FB71).

Modification of culture media can maximize the uptake capacity of the heavy metal ions by two Nostoc species.

Physiological and genomic analysis of newly-isolated polysaccharide synthesizing cyanobacterium Chroococcus sp. FPU101 and chemical analysis of the exopolysaccharide

A unicellular cyanobacterium that produces a large amount of exopolysaccharide (EPS) was isolated. The isolate, named Chroococcus sp. FPU101, grew between 20 and 30°C and at light intensities between 10 and 80 μmol m^-2 s^-1. Purified EPS from Chroococcus sp. FPU101 had a molecular size of 5.9 × 10³ kDa and contained galactose, rhamnose, fucose, xylose, mannose, glucose, galacturonic acid, and glucuronic acid at a molar ratio of 17.2:15.9:14.1:11.0:9.6:9.5:13.0:9.7. The EPS content significantly increased when the NaCl concentration in the medium was increased from 1.7 to 100 mM. However, high NaCl concentrations did not significantly affect the molecular size or chemical composition of the EPS. The genes wza, wzb, wzc, wzx, wzy, and wzz that are involved in EPS synthesis were conserved in the genome of Chroococcus sp. FPU101, which was sequenced in this study. These results suggest that the Wzy-dependent pathway is potentially involved in EPS production in this organism.

Geochemical and metagenomics study of a metal-rich, green-turquoise-coloured stream in the southern Swiss Alps

The Swiss Alpine environments are poorly described from a microbiological perspective. Near the Greina plateau in the Camadra valley in Ticino (southern Swiss Alps), a green-turquoise-coloured water spring streams off the mountain cliffs. Geochemical profiling revealed naturally elevated concentrations of heavy metals such as copper, lithium, zinc and cadmium, which are highly unusual for the geomorphology of the region. Of particular interest, was the presence of a thick biofilm, that was revealed by microscopic analysis to be mainly composed of Cyanobacteria. A metagenome was further assembled to detail the genes found in this environment. A multitude of genes for resistance/tolerance to high heavy metal concentrations were indeed found, such as, various transport systems, and genes involved in the synthesis of extracellular polymeric substances (EPS). EPS have been evoked as a central component in photosynthetic environments rich in heavy metals, for their ability to drive the sequestration of toxic, positively-charged metal ions under high regimes of cyanobacteria-driven photosynthesis. The results of this study provide a geochemical and microbiological description of this unusual environment in the southern Swiss Alps, the role of cyanobacterial photosynthesis in metal resistance, and the potential role of such microbial community in bioremediation of metal-contaminated environments.

Cyanobacterial natural products as sources for antiviral drug discovery against COVID-19

The recent Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), positive-sense RNA viruses, originated from Wuhan City in December 2019 and propagated widely globally. Hence, the disease caused by this virus has been declared as a global pandemic by the WHO. As of 18th February 2021, at least seven different vaccines across three platforms have been rolled out in countries and more than 200 additional vaccine candidates have been in development, of which more than 60 are at the stage of the clinical development. So far, Most of the approved vaccine manufacturers are Pfizer, AstraZeneca, and Serum Institute of India, which have been finalized by WHO. Synthetic drug-associated complications have evoked scientific attention for natural product-based drugs. There has been a surge in the antiviral compounds from natural resources along with some therapies. Cyanobacteria are the fruitful reservoir of many metabolites like sulfated polysaccharides and lectins that possess strong antiviral activities and immunity boosting effects. However, the research in this field has been relatively under-developed. The current research highlights important features of cyanobacterial antiviral biomaterials, benefits and drawbacks of cyanobacterial drugs, challenges, future perspectives as well as overview of drugs against COVID-19. In addition, we have described mutated variants and transmission rate of coronaviruses. The current research suggests that cyanobacterial species and their extracts have promising applications as potentially antiviral drug biomaterials against COVID-19.Communicated by Ramaswamy H. Sarma.

New procedure for separation and analysis of the main components of cyanobacterial EPS

Phototrophic biofilms produce a matrix of extracellular polymeric substances (EPS), which holds the cells together and functions inter alia as nutrient storage and protection layer. EPS mainly consist of water, polysaccharides, proteins, lipids and nucleic acids as well as lysis and hydrolysis products which makes the composition very complex. Thus, rough simplifications are used and commonly one or at most two components of the EPS are examined. In this work a new procedure for separation and analysis of EPS in the main components (i) polysaccharides, (ii) proteins and (iii) lipids is presented with recovery rates of nearly 100 %. The method was established with synthetic EPS, which based on the composition of real EPS described in literature. Afterwards, the method was transferred to real EPS samples allowing a deeper insight in the composition of EPS from only one sample. The composition of EPS-extracts from Nostoc spec, cultivated under heterotrophic and mixotrophic batch and fed-batch conditions, was analysed during a cultivation period of 14 days. It was observed that mixotrophic cultivation led to higher amounts of carbohydrates, lipids and proteins than heterotrophic cultivation respectively, regardless of batch or fed-batch culture. While the amount of proteins in the EPS increased during the cultivation period, carbohydrates and lipids were dominant in the beginning and decreased afterwards.

The prospect of using the cyanobacterium Nostoc muscorum to improve vital activity of barley seedlings by various methods of seed treatment

The influence of the cyanobacterium Nostoc muscorum on vital activity of barley seedlings of the species Novichok was researched. In the experiments different ways of cyanobacterial treatment were used: introducing microorganisms in the growth medium and pre-sowing inoculation of barley seeds with cyanobacteria. The influence of cyanobacterial treatment on biochemical indices and linear growth of barley plants was assessed. The share of plastid pigments and intensity of the processes of lipid peroxidation were assessed in a spectrophotometric way, standard methods were applied. It was stated that Nostoc muscorum has a phytostimulating effect which consists in inhibiting oxidation processes in barley cells, accumulating substances with antioxidative activity, and activating growth processes. Pre-sowing inoculation of barley seeds with cyanobacteria is the most effective one.

Structural characterization and functional properties of novel exopolysaccharide from the extremely halotolerant Halomonas elongata S6

Production of extracellular polysaccharides by halophilic Archaea and Bacteria has been widely reported and the members of the genus Halomonas have been identified as the most potential producers. In the present work, a novel exopolysaccharide (EPS-S6) produced by the extremely halotolerant newly isolated Halomonas elongata strain S6, was characterized. According to the HPAE-PAD results, EPS-S6 was mainly composed of glucosamine, mannose, rhamnose and glucose (1:0.9:0.7:0.3). EPS-S6 was highly negatively charged and its molecular weight was about 270 kDa. Studies on its functional properties showed that EPS-S6 had several potential features. It has noticeable antioxidant activities on 2,2-diphenyl-1-picrylhydrazyl (DPPH^•) inhibition and DNA protection, good ability to inhibit and to disrupt pathogenic biofilms, excellent flocculation of kaolin suspension and interesting emulsifying properties at acidic, neutral and basic pH. Therefore, EPS-S6 could have potential biotechnological concern in several fields such as in food, cosmetic and environmental industries.

Exopolysaccharides from Cyanobacteria: Strategies for Bioprocess Development

Cyanobacteria have the potential to become an industrially sustainable source of functional biopolymers. Their exopolysaccharides (EPS) harbor chemical complexity, which predicts bioactive potential. Although some are reported to excrete conspicuous amounts of polysaccharides, others are still to be discovered. The production of this strain-specific trait can promote carbon neutrality while its intrinsic location can potentially reduce downstream processing costs. To develop an EPS cyanobacterial bioprocess (Cyano-EPS) three steps were explored: the selection of the cyanobacterial host; optimization of production parameters; downstream processing. Studying the production parameters allow us to understand and optimize their response in terms of growth and EPS production though many times it was found divergent. Although the extraction of EPS can be achieved with a certain degree of simplicity, the purification and isolation steps demand experience. In this review, we gathered relevant research on EPS with a focus on bioprocess development. Challenges and strategies to overcome possible drawbacks are highlighted.

Effect of iron treatment and equilibrium pH on the kinetics of removal of some substituted phenols from synthetic wastewater onto Nostoc sp. biomass

Substituted phenols, such as 4-Nitrophenol (4-NP) and 2,4-Dichlorophenol (2,4-DCP), that are present in industrial wastewaters are considered as priority pollutants due to their toxic effects. Their removal by biosorption presents an eco-friendly, cost-effective method. The kinetics of removal of 4-NP and 2,4-DCP by untreated Nostoc sp. (UNB) and Fe-treated Nostoc sp. biomass (FNB) were studied at three different pH (4.0, 7.0 and 9.0). The highest sorption of both phenols (2.28 mg 4-NP and 1.51 mg 2,4-DCP g^-1) coupled with the lowest cumulative percentage desorption was recorded with FNB at pH 7.0. The sorption of both phenols by UNB and FNB was best accounted for by pseudo-second-order kinetics. Compared to UNB, FNB had significantly higher equilibrium sorption capacities for both phenols at all the three pH values and also higher sorption rate constants of 4-NP at pH 4 and 9 and of 2,4-DCP at pH 4 and 7. The Fourier transform infrared spectroscopy (FTIR) analysis showed that -OH and COO^- groups of UNB interacted with Fe⁺³. The sorption of 4-NP and 2,4-DCP on UNB was likely through H-bonding/structural cation bridging with the phenolic group, while their sorption onto FNB appeared to be a complexation reaction with very low reversibility.

Heterologous Expression of Ethanol Synthesis Pathway in Glycogen Deficient Synechococcus elongatus PCC 7942 Resulted in Enhanced Production of Ethanol and Exopolysaccharides

In this study, the Synechococcus elongatus PCC 7942 (hereafter S. elongatus) was engineered by the glgC knockout as well as the insertion of the pdc-adh genes from two different microorganisms. The insertion of pdc-adh genes increased the ethanol synthesis with further improvement in the productivity upon the destruction of glycogen synthesis pathway and the supplementation of cofactor. The abolition of glycogen synthesis pathway led to a considerable increase of the engineered S. elongatus metabolites involved in the ethanol synthesis pathway. Moreover, the studies on cofactor addition highlighted the importance of Mg+2, Zn+2, thiamine pyrophosphate, and NADP+ in ethanol synthesis. The yields of 3856 mg/L ethanol and 109.5 µg/108 cells exopolysaccharides were obtained in the engineered S. elongatus using a photo-bioreactor under optimized conditions. This enhanced production in ethanol and exopolysaccharides are attributed to the flux of carbon from glycogen synthesis pathway and proper availability of essential components.

Strategies to Obtain Designer Polymers Based on Cyanobacterial Extracellular Polymeric Substances (EPS)

Biopolymers derived from polysaccharides are a sustainable and environmentally friendly alternative to the synthetic counterparts available in the market. Due to their distinctive properties, the cyanobacterial extracellular polymeric substances (EPS), mainly composed of heteropolysaccharides, emerge as a valid alternative to address several biotechnological and biomedical challenges. Nevertheless, biotechnological/biomedical applications based on cyanobacterial EPS have only recently started to emerge. For the successful exploitation of cyanobacterial EPS, it is important to strategically design the polymers, either by genetic engineering of the producing strains or by chemical modification of the polymers. This requires a better understanding of the EPS biosynthetic pathways and their relationship with central metabolism, as well as to exploit the available polymer functionalization chemistries. Considering all this, we provide an overview of the characteristics and biological activities of cyanobacterial EPS, discuss the challenges and opportunities to improve the amount and/or characteristics of the polymers, and report the most relevant advances on the use of cyanobacterial EPS as scaffolds, coatings, and vehicles for drug delivery.

Estimation of growth and exopolysaccharide production by two soil cyanobacteria, Scytonema tolypothrichoides and Tolypothrix bouteillei as determined by cultivation in irradiance and temperature crossed gradients

Two filamentous cyanobacteria of the genera Scytonema and Tolypothrix were reported to be effective for stabilizing soil in arid areas due to the production of significant amounts of extracellular polysaccharides (EPS). These EPS may also have applications in the biotechnology industry. Therefore, two cyanobacterial species, Scytonema tolypothrichoides and Tolypothrix bouteillei were examined using crossed gradients of temperature (8-40°C) and irradiance (3-21 W m^-2) to identify their temperature and irradiance optima for maximum biomass and EPS production. According to their reported temperature requirements, both strains were considered mesophilic. The optimum growth range of temperature in S. tolypothrichoides (27 to 34°C) was higher than T. bouteillei (22-32°C). The optimum irradiance range for growth of S. tolypothrichoides (9-13 W m^-2) was slightly lower than T. bouteillei (7-18 W m^-2). Maximum EPS production by S. tolypothrichoides occurred at similar temperatures (28-34°C) as T. bouteillei (27-34°C), both slightly higher than for maximum growth. The optimum irradiance range for EPS production was comparable to that for growth in S. tolypotrichoides (8-13 W m^-2), and slightly lower in T. bouteillei (7-17 W m^-2). The Redundancy Analysis confirmed that temperature was the most important controlling factor and protocols for field applications or for mass cultivation can now be developed.

Effects of Phosphorus in Growth Media on Biomineralization and Cell Surface Properties of Marine Cyanobacteria Synechococcus

Through geological time, cyanobacterial picoplankton have impacted the global carbon cycle by sequestrating CO2 and forming authigenic carbonate minerals. Various studies have emphasized the cyanobacterial cell envelopes as nucleation sites for calcium carbonate formation. Little is known, however, about how environmental conditions (e.g., nutrient content) trigger a cell surface and its properties and, consequently, influence biomineralization. Our study aims to understand how phosphorus (P) concentration impacts the properties of cell surfaces and cell–mineral interactions. Changes to the surface properties of marine Synechococcus strains grown under various P conditions were characterized by potentiometric titrations, X-ray photoelectron spectroscopy (XPS), and tip-enhanced Raman spectroscopy (TERS). Biomineralization experiments were performed using cyanobacterial cells, which were grown under different P concentrations and exposed to solutions slightly oversaturated with respect to calcium carbonate. We observed the changes induced by different P conditions in the macromolecular composition of the cyanobacteria cell envelope and its consequences for biomineralization. The modified properties of cell surfaces were linked to carbonate precipitation rates and mineral morphology from biomineralization experiments. Our analysis shows that the increase of phosphoryl groups and surface charge, as well as the relative proportion of polysaccharides and proteins, can impact carbonate precipitation by picocyanobacteria.

Pilot-scale isolation and characterization of extracellular polymeric substances (EPS) from cell-free medium of Spirulina sp. LEB-18 cultures under outdoor conditions

This objective of this work was to monitor the EPS production during the growth of Spirulina sp. LEB-18, evaluate the productivity and to characterize the exopolymers obtained on pilot-scale under outdoor conditions. The production of crude EPS occurred in all phases of biomass growth and was approximately ten folds higher than that biomass concentration of Spirulina sp. LEB-18 at the end cultivation, demonstrating the importance of the use of supernatant after harvesting of Spirulina to obtain high value bioproducts. The EPS extracted by Spirulina sp. LEB-18 are typically heteropolymers with one high molecular weight fraction (polysaccharides) with potential to be utilized as an alternative bioflocculant and another fraction of lower molecular mass (proteins). The presence of uronic acids, pyruvates and acyl groups of carbohydrates or carboxylic groups of amino acids in protein moiety is the main responsible for overall negative charge of EPS, which is also of biotechnological importance. Moreover, due to the pseudoplastic behavior of the solutions and high thermal stability, the obtained EPS can be widely applied in several industrial sectors, thus determining its technological and market potentiality.

Physiological properties and genetic analysis related to exopolysaccharide (EPS) production in the fresh-water unicellular cyanobacterium Aphanothece sacrum (Suizenji Nori)

The clonal strains, phycoerythrin(PE)-rich- and PE-poor strains, of the unicellular, fresh water cyanobacterium Aphanothece sacrum (Suringar) Okada (Suizenji Nori, in Japanese) were isolated from traditional open-air aquafarms in Japan. A. sacrum appeared to be oligotrophic on the basis of its growth characteristics. The optimum temperature for growth was around 20°C. Maximum growth and biomass increase at 20°C was obtained under light intensities between 40 to 80 μmol m^-2 s^-1 (fluorescent lamps, 12 h light/12 h dark cycles) and between 40 to 120 μmol m^-2 s^-1 for PE-rich and PE-poor strains, respectively, of A. sacrum . Purified exopolysaccharide (EPS) of A. sacrum has a molecular weight of ca. 10⁴ kDa with five major monosaccharides (glucose, xylose, rhamnose, galactose and mannose; ≥85 mol%). We also deciphered the whole genome sequence of the two strains of A. sacrum. The putative genes involved in the polymerization, chain length control, and export of EPS would contribute to understand the biosynthetic process of their extremely high molecular weight EPS. The putative genes encoding Wzx-Wzy-Wzz- and Wza-Wzb-Wzc were conserved in the A. sacrum strains FPU1 and FPU3. This result suggests that the Wzy-dependent pathway participates in the EPS production of A. sacrum.

Development of Functional Bionanocomposites Using Cyanobacterial Polysaccharides

Cyanobacteria are regarded as very eco-friendly microreactors for the production of various biomolecules such as polysaccharides by fixing not only carbon but also nitrogen in water. Cyanobacterial polysaccharides having various functional groups such as hydroxyls, carboxyls, sulfates, etc. have the ability to interact with metals or inorganics, to create bionanocomposites. Sacran, a supergiant cyanobacterial anionic polysaccharide extracted from the extracellular matrix of Aphanothece sacrum which is mass-cultivated in freshwater, is mainly used to create functional bionanocomposites. Gel-type bionanocomposites of sacran with various metal cations are formed and showed photoresponsive functions. Metal recovery is performed from the sacran bionanocomposite gels. Sacran chains are complexed with multi-wall carbon nanotubes (MWCNT) to give viscose dispersion from which MWCNT bionanocomposites can be collected by electrophoresis. The MWCNT/sacran dispersion retains the capability of adsorbing various metal ions to form hardened hydrogel beads. Finally, natural inorganic sepiolite can be used for sacran bionanocomposites which show an efficient neodymium ion adsorption ability. Thus, cyanobacterial polysaccharides are useful for preparing eco-friendly and functional bionanocomposites with various hard materials.

Preparation and Characterization of Polysaccharide Films from the Cyanobacteria Nostoc commune

Nostoc Commune bacteria release a variety of polysaccharides into the culture medium during cell growth. In this paper we report, for the first time, the use of these polysaccharides as a raw material for the preparation of biopolymeric films. The structural characterization of the films prepared was assessed by FTIR and 1H-NMR. XRD and thermal analysis tests showed that these films are amorphous and have a glass transition temperature of −25°C. Tensile tests showed that NCP films displayed a similar mechanical behavior in comparison with other natural biopolymer films. These results suggest that these NCP films can be used for the development of new biopolymeric materials with potential applications in the food and biomedical industries.

The green alga Dictyosphaerium chlorelloides biomass and polysaccharides production determined using cultivation in crossed gradients of temperature and light

The green microalga Dictyosphaerium chlorelloides was identified as promising microorganism for biotechnological production of exopolysaccharides (EPS). In stationary phase the culture suspension solidifies to thick gel, with very high viscosity and high content of EPS which may be interesting for many biotechnological applications. To develop cultivation protocol for maximum biomass/polysaccharide production, the optimum conditions for growth and polysaccharides production were determined in this study using the crossed gradient cultivation method. Temperature and irradiance requirements of Dictyosphaerium chlorelloides were evaluated by statistical analyses for growth rate/biomass, extracellular (EPS) and intracellular (IPS) polysaccharides contents in crossed gradients of temperature (4-45°C) and irradiance (2-18 W/m², 9.1 - 82.3 μmol/(m² s)). The maximum relative growth rate was observed at temperatures around 19.2°C and relatively low irradiances in range 2.6-11 W/m² (11.9-50.3 μmol/(m² s)). The maximum IPS production was observed at temperatures around 19.2°C and irradiance around 11 W/m² (50.3 μmol/(m² s)). The maximum production of EPS was observed at temperatures around 25.7°C and similar irradiances as IPS production. Due to temperature separation of growth and EPS production, development of cultivation protocol based controlled temperature manipulation is possible.

Exopolysaccharides extracted from Parachlorella kessleri inhibit colon carcinoma growth in mice via stimulation of host antitumor immune responses

The newly purified extracellular polysaccharides (exopolysaccharides) from Parachlorella kessleri (PCEPS) were evaluated on their antitumor and immunomodulatory effects in cell culture and mouse colon carcinoma peritoneal dissemination model. In two-dimensional cell culture, the PCEPS treatment inhibited cell growth of both murine and human colon carcinoma cells in a dose- and time-dependent manner. In contrast, the growth of mouse splenocytes (SPLs) and bone marrow cells (BMCs) were stimulated by the treatment with PCEPS. The treatment with PCEPS also increased specific subpopulations of the cells in BMCs: antigen presenting cells (CD19⁺ B cells, 33D1⁺ dendritic cells and CD68⁺ macrophage) and CD8⁺ cytotoxic T cells. In three-dimensional spheroid culture, spheroid growth of CT26 cells co-cultured with HL-60 human neutrophilic promyeloblasts and Jurkat cells (human lymphoblasts), but not THP-1 human monocyte/macrophage was significantly attenuated by PCEPS treatment. In a mouse CT26 colon carcinoma peritoneal dissemination model, intraperitoneal injection of PCEPS (10 mg/kg, twice per week) significantly attenuated the growth of CT26 colon carcinoma in syngeneic mice. The present study suggests that PCEPS inhibits colon carcinoma growth via direct cell growth inhibition and a stimulation of the host antitumor immune responses. Taken together, the current study suggests that exopolysaccharides derived from Parachlorella kessleri contain significant bioactive materials that inhibit colon carcinoma growth.

Optical second-harmonic images of sacran megamolecule aggregates

We have detected a second-order nonlinear optical response from aggregates of the ampholytic megamolecular polysaccharide sacran extracted from cyanobacterial biomaterials by using optical second-harmonic-generation (SHG) microscopy. The SHG images of sacran cotton-like lump, fibers, and cast films showed SHG intensity microspots of several tens of micrometers in size. The dependence of the SHG spot intensity on an excitation light polarization angle was observed to illustrate sacran molecular orientation in these microdomains. We also observed SHG signals around a special region of the cast film edges of sacran. These results show that sacran megamolecules aggregate in several different ways.

Biosafety of biotechnologically important microalgae: intrinsic suicide switch implementation in cyanobacterium Synechocystis sp. PCC 6803

In recent years, photosynthetic autotrophic cyanobacteria have attracted interest for biotechnological applications for sustainable production of valuable metabolites. Although biosafety issues can have a great impact on public acceptance of cyanobacterial biotechnology, biosafety of genetically modified cyanobacteria has remained largely unexplored. We set out to incorporate biocontainment systems in the model cyanobacterium Synechocystis sp. PCC 6803. Plasmid-encoded safeguards were constructed using the nonspecific nuclease NucA from Anabaena combined with different metal-ion inducible promoters. In this manner, conditional lethality was dependent on intracellular DNA degradation for regulated autokilling as well as preclusion of horizontal gene transfer. In cells carrying the suicide switch comprising the nucA gene fused to a variant of the copM promoter, efficient inducible autokilling was elicited. Parallel to nuclease-based safeguards, cyanobacterial toxin/antitoxin (TA) modules were examined in biosafety switches. Rewiring of Synechocystis TA pairs ssr1114/slr0664 and slr6101/slr6100 for conditional lethality using metal-ion responsive promoters resulted in reduced growth, rather than cell killing, suggesting cells could cope with elevated toxin levels. Overall, promoter properties and translation efficiency influenced the efficacy of biocontainment systems. Several metal-ion promoters were tested in the context of safeguards, and selected promoters, including a nrsB variant, were characterized by beta-galactosidase reporter assay.

Summary: Biosafety of biotechnologically important microalgae was addressed by suicide switch implementation in cyanobacterium Synechocystis sp. PCC 6803. This is the first report of biocontainment safeguards in cyanobacteria.

Microbially-driven strategies for bioremediation of bauxite residue

Globally, 3 Gt of bauxite residue is currently in storage, with an additional 120 Mt generated every year. Bauxite residue is an alkaline, saline, sodic, massive, and fine grained material with little organic carbon or plant nutrients. To date, remediation of bauxite residue has focused on the use of chemical and physical amendments to address high pH, high salinity, and poor drainage and aeration. No studies to date have evaluated the potential for microbial communities to contribute to remediation as part of a combined approach integrating chemical, physical, and biological amendments. This review considers natural alkaline, saline environments that present similar challenges for microbial survival and evaluates candidate microorganisms that are both adapted for survival in these environments and have the capacity to carry out beneficial metabolisms in bauxite residue. Fermentation, sulfur oxidation, and extracellular polymeric substance production emerge as promising pathways for bioremediation whether employed individually or in combination. A combination of bioaugmentation (addition of inocula from other alkaline, saline environments) and biostimulation (addition of nutrients to promote microbial growth and activity) of the native community in bauxite residue is recommended as the approach most likely to be successful in promoting bioremediation of bauxite residue.

Role of cyanobacterial exopolysaccharides in phototrophic biofilms and in complex microbial mats

Exopolysaccharides (EPSs) are an important class of biopolymers with great ecological importance. In natural environments, they are a common feature of microbial biofilms, where they play key protective and structural roles. As the primary colonizers of constrained environments, such as desert soils and lithic and exposed substrates, cyanobacteria are the first contributors to the synthesis of the EPSs constituting the extracellular polymeric matrix that favors the formation of microbial associations with varying levels of complexity called biofilms. Cyanobacterial colonization represents the first step for the formation of biofilms with different levels of complexity. In all of the possible systems in which cyanobacteria are involved, the synthesis of EPSs contributes a structurally-stable and hydrated microenvironment, as well as chemical/physical protection against biotic and abiotic stress factors. Notwithstanding the important roles of cyanobacterial EPSs, many aspects related to their roles and the relative elicited biotic and abiotic factors have still to be clarified. The aim of this survey is to outline the state-of-the-art of the importance of the cyanobacterial EPS excretion, both for the producing cells and for the microbial associations in which cyanobacteria are a key component.

Draft Genome Sequence of Exopolysaccharide-Producing Cyanobacterium Aphanocapsa montana BDHKU 210001

We report for the first time the draft genome sequence of Aphanocapsa montana BDHKU 210001, a halotolerant cyanobacterium isolated from India. This is a marine exopolysaccharide (EPS)-producing cyanobacterium. The genome of this species is assembled into 11.50 million bases, with 296 scaffolds carrying approximately 7,296 protein-coding genes.

Association of heterotrophic bacteria with aggregated Arthrospira platensis exopolysaccharides: implications in the induction of axenic cultures

Inducing an axenic culture of the edible cyanobacterium Arthrospira (Spirulina) platensis using differential filtration alone is never successful; thus, it has been thought that, in non-axenic cultures, a portion of contaminating bacteria is strongly associated with Arthrospira cells. However, examination of the behavior of these bacteria during filtration revealed that they were not associated with Arthrospira cells but with aggregates of exopolysaccharides present in the medium away from the Arthrospira cells. Based on this finding, a rapid and reliable method for preparing axenic trichomes of A. platensis was established. After verifying the axenicity of the resulting trichomes on enriched agar plates, they were individually transferred to fresh sterile medium using a handmade tool, a microtrowel, to produce axenic cultures. With this technique, axenic cultures of various A. platensis strains were successfully produced. The technique described in this study is potentially applicable to a wider range of filamentous cyanobacteria.

Exopolymers from Tolypothrix tenuis and three Anabaena sp. (Cyanobacteriaceae) as novel blood clotting agents for wound management

Rapid initiation of clotting is critical to trauma patients. In the present study exopolymers (EPs) from four desert cyanobacteria including Tolypothrix tenuis and three species of Anabaena have been discovered as potential hemostatic biomaterials. The EPs showed reduction in activated partial thromboplastin time (APTT) and prothrombin time (PT) by 16-41% and 12-65%, respectively. Besides hastening blood clotting, the EPs could absorb 7.1-25.9 g H₂O g(-1) EP and displayed 7.1-18.1% hydrophobicity. They were noncytotoxic and biodegradable. The EP from Anabaena sp. showed strong antibacterial activity against E. coli, S. aureus and B. licheniformis. These results suggest that cyanobacteria, the microscopic phototrophs growing rapidly over simple mineral medium could prove to be a novel source of affordable hemostatic dressings for the traumatic wounds in underdeveloped and developing countries. Compositional analysis of the EPs showed them to be consisting of mainly carbohydrate (17-50%), protein (4.4-7.2%), uronic acid (4.7-9.5%) and sulphate (0.6-6.6%). Their viscometric molecular weight ranged from 539 to 3679 kDa. They were further characterized using GC-MS and FTIR.

Marine polysaccharides in microencapsulation and application to aquaculture: "from sea to sea"

This review's main objective is to discuss some physico-chemical features of polysaccharides as intrinsic determinants for the supramolecular structures that can efficiently provide encapsulation of drugs and other biological entities. Thus, the general characteristics of some basic polysaccharides are outlined in terms of their conformational, dynamic and thermodynamic properties. The analysis of some polysaccharide gelling properties is also provided, including the peculiarity of the charged polysaccharides. Then, the way the basic physical chemistry of polymer self-assembly is made in practice through the laboratory methods is highlighted. A description of the several literature procedures used to influence molecular interactions into the macroscopic goal of the encapsulation is given with an attempt at classification. Finally, a practical case study of specific interest, the use of marine polysaccharide matrices for encapsulation of vaccines in aquaculture, is reported.

Using extracellular polymeric substances (EPS)-producing cyanobacteria for the bioremediation of heavy metals: do cations compete for the EPS functional groups and also accumulate inside the cell?

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&emsp14;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.

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

The cyanobacterium Gloeothece sp. strain PCC 6909 and its sheathless mutant were tested for their abilities to remove copper ions from aqueous solutions, with the aim of 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 (released exocellular polysaccharides [RPS]) into the culture medium. The RPS of the wild type and the mutant are composed of the same 11 sugars, although they are present in different amounts, and the RPS of the mutant possesses a larger amount of acidic sugars and a smaller amount of deoxysugars than the wild type. Unexpectedly, whole cultures of the mutant were more effective in the removal of the heavy metal than the wild type (46.3 +/- 3.1 and 26.7 +/- 1.5 mg of Cu(2+) 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 rather than to the sheath. Therefore, the increased copper binding efficiency observed with the sheathless mutant can be attributed to the release of a polysaccharide containing larger amounts and/or more accessible functional groups (e.g., carboxyl and amide groups).

Biosorption of uranium by lake-harvested biomass from a cyanobacterium bloom

The aim of this work was to study some basic aspects of uranium biosorption by powdered biomass of lake-harvested cyanobacterium water-bloom, which consisted predominantly of Microcystis aeruginosa. The optimum pH for uranium biosorption was between 4.0 and 8.0. The batch sorption reached the equilibrium within 1 h. The isotherm fitted the Freundlich model well. Although the Langmuir model fitted the experiment data well at pH 3.0, 5.0 and 7.0, it did not fit at pH 9.0 and 11.0 at all. This implies that different biosorption mechanisms may be involved at different pH values. 0.1 N HCl was effective in uranium desorption. The results indicated that the naturally abundant biomass of otherwise nuisance cyanobacterium bloom exhibited good potential for application in removal of uranium from aqueous solution.