Freshwater Cyanobacteria Research Articles

Isolation and Characterization of the Chromatic-Acclimating, Filamentous Cyanobacterium Pseudanabaena sp. Strain SR411.

We isolated Pseudanabaena sp. Strain SR411, a novel filamentous, nonheterocystous, freshwater cyanobacterium from the West Branch of the Susquehanna River in Pennsylvania. Analysis of phycobilisome protein accumulation indicates Pseudanabaena SR411 acclimates to changing light wavelengths and we classified it as a chromatic acclimating cyanobacterium type CA3. The 5,780,083 bp genome has a GC content of 42.2% in which we identified 5,218 coding sequences and 58 RNA sequences. The genome includes putative homologs to the CA3 regulatory proteins RcaE, RcaF and RcaC.

Alleviating effects of microplastics together with tetracycline hydrochloride on the physiological stress of Closterium sp.

Microplastics have significant influence on both freshwater cyanobacteria and marine microalgae, especially under co-exposure with other pollutants such as heavy metals, antibiotics, and pharmaceuticals. In the present study, combined effects of microplastics (polyethylene terephthalate (PET) or polybutylene terephthalate (PBT)) and tetracycline hydrochloride (TCH) on the microalgae Closterium sp. were studied to evaluate their acute toxicity, and the cell density, total chlorophyll concentration, photosynthetic activity, antioxidant system, and subcellular structure of Closterium sp. under different treatments were used to explain the physiological stress mechanism of the combined effects. The results indicate that both the single and combined treatments have inhibition effects on the cell growth and photosynthetic activity, with inhibition efficiencies (in terms of cell density) of 5.0%, 9.2%, 66.7%, 55.1%, and 59.8% for PET (100 mg L-1), PBT (100 mg L-1), TCH (10 mg L-1), PET/TCH (PET 100 mg L-1 and TCH 10 mg L-1), and PBT/TCH (PBT 100 mg L-1 and TCH 10 mg L-1), respectively, and relative electron-transport rates (rETRs) of 7.3%, 12.7%, 66.8%, 54.0%, and 59.9%, respectively, for each treatment compared with the control on the 7th day. Moreover, both PET and PBT have positive effects in alleviating TCH toxicity toward Closterium sp., and at the same time, the malondialdehyde level (MDA), superoxide dismutase (SOD) activity, and catalase (CAT) activity induced by the combined treatments were much higher than those from the single microplastic treatments but lower than those from TCH treatment after 7 days. It was demonstrated that TCH causes a much more serious oxidative stress than PET/TCH and PBT/TCH, and the lower oxidative stress of the PET/TCH and PBT/TCH groups could be attributed to the adsorption of TCH to PET or PBT. This work improves the understanding of the combined toxicity effects of microplastics and TCH on Closterium sp.

Up to Date of Cyanobacterial Natural Products

More than 2000 compounds have been reported from cyanobacteria. The most successful example is dolastatin 10, of which a related compound monomethylauristatin E is used as antibody-drug conjugate (ADC) for Hodgkin lymphoma and systemic anaplastic large cell lymphoma. Recently genome-based analyses by Piel led to the discovery of novel compounds from cyanobacteria. W. H. Gerwick found a potential as anti-SARS-CoV-2 agent in gallinamide A, which was reported as a cathepsin L inhibitor. In our group columbamides were isolated from the marine cyanobacterium Moorena bouillonii. The geometry of the double bond was determined by the coupling constant obtained using non-decoupled heteronuclear single quantum coherence (HSQC). The configuration of chloromethine in a long-chain acyl moiety was determined by the Ohrui method at room temperature using a chiral HPLC column. Columbamide D showed biosurfactant activity. One strain many compounds (OSMAC) is a method to discover new compounds by changing culture conditions. Prior to our experiments, attempts to apply OSMAC in cyanobacteria resulted in the induction or up-regulation of only known compounds. The heat shock culture of the freshwater cyanobacterium Microcystis aeruginosa up-regulated a ribosomal peptide argicyclamide C. At the same time, we discovered bis-prenylated and monoprenylated argicyclamides A and B. More recently iron-limited culture produced hydroxylated argicyclamide A. OSMAC and genome-based screening could lead the discovery of unique biologically active compounds from cyanobacteria.

Growth of freshwater cyanobacterium Aphanizomenon sp. ULC602 in different growing and nutrient conditions.

Aphanizomenon sp. ULC602, recently isolated in a Belgian lake, is a filamentous, nitrogen-fixing, freshwater cyanobacterium that is one of the primary producers of cyanotoxins following its bloom formation, causing water contamination. This study aims to evaluate the effects of growing conditions and essential nutrients on the growth of Aphanizomenon sp. ULC602 via its production of chlorophyll-a (Chlo-a). Our results indicated that this bacterium could grow well at temperatures ranging from 18 to 25°C with an optimal pH of 6.0-7.5 under continuous lighting. It grew slowly in the absence of a carbon source or at lower carbon concentrations. The addition of nitrogen from nitrate and urea led to a less than 50% reduction of Chlo-a content compared to the medium lacking nitrogen. The iron bioavailability significantly stimulated the Chlo-a production, but it was saturated by an iron concentration of 0.115 mM. Moreover, a decrease in Chlo-a biomass was observed under sulfur deficiency. The bacterium could not grow well in media containing various phosphorus sources. In conclusion, as the growth and consequent forming bloom of cyanobacteria can be stimulated or inhibited by environmental conditions and eutrophication, our investigation could contribute to further studies to control the blooming of the target bacterium in freshwater.

Landfill leachate treatment using single and mixed freshwater cyanobacterial isolates

The increasing volume of waste disposal and improper management of landfill has been contributing to the heavily polluted leachate. Local freshwater cyanobacteria were identified based on the polyphasic approach that combines morphological and molecular identification by the 16S rRNA gene sequencing method. The local cyanobacteria isolate (A1) was identified as the genus Cyanobacterium of the order Chroococcales. The A1 isolate together with identified cyanobacteria, Anabaena sp. was used to observe their effectiveness in remediating leachate pollution either as monoculture or in mixed culture. Prior to the phycoremediation, the characterization of leachate had been carried out. The biological oxygen demand (BOD5), chemical oxygen demand (COD), pH value, concentration of ammonia-nitrogen (NH3-N), nitrite , and nitrate of the raw leachate determined were 22.37 mg/L, 58.33 mg/L, 7.84, 82.7 mg/L, 88.67mg/L and 89.43mg/L, respectively. The use of a single Anabaena sp. demonstrates the most effective in the removal of all contaminants that exist in the leachate. The removal of COD was the highest at 105.71% followed by BOD5 at 92.71% and NO3- at 82.09%. This finding suggested that in order to achieve optimum removal of BOD5, COD, NH3-N, NO2 - and NO3 - content in leachate sample, treatment by Anabaena sp. should be applied.

Identification of Desiccation Stress-Inducible Antioxidative and Antiglycative Ultraviolet-Absorbing Oxylipins, Saclipin A and Saclipin B, in an Edible Cyanobacterium Aphanothece sacrum.

Aphanothece sacrum, a freshwater cyanobacterium, is an edible cyanobacterial strain. We identified two compounds belonging to the oxylipin family that possess UV-absorbing abilities and accumulate in the dried sample of A. sacrum. The compounds, named saclipin A and saclipin B, exhibited strong UV-absorption properties with the absorption maxima at 316 and 319 nm, respectively, and the molar extinction coefficients of 26,454 and 30,555 M-1 cm-1, respectively. The chemical structures of saclipins A and B have been elucidated, revealing that they have an all-E and a 12Z isomeric relationship within the triene structure. The saclipins could be isomerized by photoirradiation, with the cis-form saclipin B proving to be more stable in methanol, ethanol, or acetonitrile. Under drought stress conditions, the accumulation of saclipins A and B in A. sacrum was found to be increased 20- and 10-fold, respectively. Purified saclipins from A. sacrum showed biocompatibility and valuable bioactivities. Specifically, saclipins exhibited radical scavenging activity, maintaining their activity even 40 min after the reaction began. Additionally, they demonstrated inhibitory activity against glycation of elastin and collagen, which are constituents of dermal tissue. Notably, saclipins showed higher activity than the well-known glycation inhibitor aminoguanidine against collagen glycation.

Proto-dolomite spherulites with heterogeneous interior precipitated in brackish water cultivation of freshwater cyanobacterium Leptolyngbya boryana

Primary dolomite is believed to be formed through cyanobacterial calcification, yet the details and mechanisms of this process are not fully understood. In this study, a freshwater filamentous cyanobacterium, Leptolyngbya boryana, was cultured and domesticated in artificial freshwater and brackish solutions with various Mg/Ca ratios. The hydrochemistry, the extracellular polymeric substance (EPS) composition, and precipitate mineralogy in the medium were monitored. The results showed that the L. boryana induced proto-dolomite precipitation in brackish medium with salinity of 1.5 % and Mg/Ca ratio of 5. The proto-dolomite in this study has a “double spherical” appearance and a hollow core, which may have originally been filled by the complex composed of EPS and amorphous CaMg carbonate. With regard to elemental composition, the cyanobacterially-induced proto-dolomite is rich in calcium inside and magnesium-rich on the surface, and cyanobacterial organic matter is sealed inside the particles during spherulite growth. In this study, the accelerators for Mg2+ to enter the carbonate lattice mainly include extracellular acidic amino acids and polysaccharides. The changes of these promoters among different cultures were related to the growth state of cyanobacteria under salinity stress. The polysaccharides concentration has a significant increasing in the dolomite-precipitating medium, indicating that it may be the main promoter of proto-dolomite precipitation and significantly increases the amount of Mg2+ precipitation. At the meantime, the amount of precipitated Ca2+ was suppressed by increasing salinity and Mg2+, thus leading to the precipitation of proto-dolomite in this shifting process. This study can potentially provide a reference for explaining the dolomite (proto-dolomite) precipitation in aerobic brackish environment where cyanobacteria thrive.

More than just an eagle killer: The freshwater cyanobacterium Aetokthonos hydrillicola produces highly toxic dolastatin derivatives

Cyanobacteria are infamous producers of toxins. While the toxic potential of planktonic cyanobacterial blooms is well documented, the ecosystem level effects of toxigenic benthic and epiphytic cyanobacteria are an understudied threat. The freshwater epiphytic cyanobacterium Aetokthonos hydrillicola has recently been shown to produce the "eagle killer" neurotoxin aetokthonotoxin (AETX) causing the fatal neurological disease vacuolar myelinopathy. The disease affects a wide array of wildlife in the southeastern United States, most notably waterfowl and birds of prey, including the bald eagle. In an assay for cytotoxicity, we found the crude extract of the cyanobacterium to be much more potent than pure AETX, prompting further investigation. Here, we describe the isolation and structure elucidation of the aetokthonostatins (AESTs), linear peptides belonging to the dolastatin compound family, featuring a unique modification of the C-terminal phenylalanine-derived moiety. Using immunofluorescence microscopy and molecular modeling, we confirmed that AEST potently impacts microtubule dynamics and can bind to tubulin in a similar matter as dolastatin 10. We also show that AEST inhibits reproduction of the nematode Caenorhabditis elegans. Bioinformatic analysis revealed the AEST biosynthetic gene cluster encoding a nonribosomal peptide synthetase/polyketide synthase accompanied by a unique tailoring machinery. The biosynthetic activity of a specific N-terminal methyltransferase was confirmed by in vitro biochemical studies, establishing a mechanistic link between the gene cluster and its product.

The β-Lactamase Activity at the Community Level Confers β-Lactam Resistance to Bloom-Forming Microcystis aeruginosa Cells.

Many freshwater cyanobacteria, including Microcystis aeruginosa, lack several known antibiotic resistance genes; however, both axenic and xenic M. aeruginosa strains exhibited high antibiotic resistance against many antibiotics under our tested concentrations, including colistin, trimethoprim, and kanamycin. Interestingly, axenic PCC7806, although not the xenic NIBR18 and NIBR452 strains, displayed susceptibility to ampicillin and amoxicillin, indicating that the associated bacteria in the phycosphere could confer such antibiotic resistance to xenic strains. Fluorescence and scanning electron microscopic observations revealed their tight association, leading to possible community-level β-lactamase activity. Combinatory treatment of ampicillin with a β-lactamase inhibitor, sulbactam, abolished the ampicillin resistance in the xenic stains. The nitrocefin-based assay confirmed the presence of significant community-level β-lactamase activity. Our tested low ampicillin concentration and high β-lactamase activity could potentially balance the competitive advantage of these dominant species and provide opportunities for the less competitive species, thereby resulting in higher bacterial diversity under ampicillin treatment conditions. Non-PCR-based metagenome data from xenic NIBR18 cultures revealed the dominance of blaOXA-related antibiotic resistance genes followed by other class A β-lactamase genes (AST-1 and FAR-1). Alleviation of ampicillin toxicity could be observed only in axenic PCC7806, which had been cocultured with β-lactamase from other freshwater bacteria. Our study suggested M. aeruginosa develops resistance to old-class β-lactam antibiotics through altruism, where associated bacteria protect axenic M. aeruginosa cells.

Active role of the protein translation machinery in protecting against stress tolerance in Synechococcus elongatus PCC7942

In vivo protein synthesis is crucial for all domains of life. It is accomplished through translational machinery, and a key step is the translocation of tRNA-mRNA by elongation factor G (EF-G). Genome-based analysis revealed two EF-G encoding genes (S0885 and S2082) in the freshwater cyanobacterium model Synechococcus elongatus PCC7942. S0885 is the essential EF-G gene for photosynthesis. We generated a strain of S. elongatus PCC7942 that overexpressed S0885 (OX-S0885) to identify EF-G functionality. RT-PCR and Western blot analyses revealed increased transcriptional and translational levels in OX-S0885 at 10.5–13.5 and 2.0–3.0 fold, respectively. Overexpression of S0885 led to an increase in specific growth rate. Additionally, polysome-to-monosome ratio (P/M) and RNA-to-protein ratio (R/P) were elevated in OX-S0885 compared with the empty vector. Interestingly, R/P in OX-S0885 was retained at more than 70% under oxidative stress while R/P in the empty vector was severely depleted, suggesting the maintenance of translation. Thus, S0885 appeared to be the important target of oxidative stress because it was protected by the stress response system to maintain its function. These results suggest that cyanobacterial EF-G has a primary function in translation and an unrelated activity during stress conditions. These findings support the substantial role of EF-G in the formation and maintenance of cellular protein formation, and in the protection of the global translational mechanism under oxidative stress condition.

Heat shock and iron limitation modulate the metabolic profile of the cyanobacterium Microcystis aeruginosa NIES‐88

AbstractThe freshwater cyanobacterium Microcystis aeruginosa NIES‐88, which can produce microcystins, micropeptins, and argicyclamides, was subjected to a one strain many compounds (OSMAC) analysis. We report its response to two environmental stressors, temperature and iron limitation, by means of untargeted and targeted metabolomics. The results demonstrated a slower specific growth rate of 0.20 per day and 0.16 per day in adverse conditions of 37°C and iron limitation, respectively. The metabolic signature of M. aeruginosa was highly dependent on incubation temperatures. Production of microcystins LR and RR was severely downregulated while that of argicyclamide B was significantly upregulated, with a highest 10‐fold increase on day 14 of heat shock treatment. M. aeruginosa NIES‐88 was found to produce a new compound, argicyclamide D (1), in iron limited medium, which has the same macrocyclic structure as the previously reported analogs. Hence, it is proposed that acclimation of M. aeruginosa to environmental stressors might be mediated by a change in the metabolic pathways as well as modulation of the levels of their expressed metabolites.

Role of the Lethabo Weir in altering the phytoplankton community structure of the Vaal River, South Africa

During 2012, aerial photographs of the Vaal River, South Africa, showed differences in water colour on either side of the Lethabo Weir. Water upstream of the weir was muddy brown, while water downstream was olive-green. Physical and chemical analyses indicated water quality differences upstream and downstream from the weir; furthermore, microscopic examination of water samples revealed that the colour difference were the result of different types of phytoplankton blooms. The upstream section was dominated by cryptophytes and green algae, while the downstream section experienced a cyanobacterial bloom dominated by Microcystis aeruginosa. The same phenomenon was again observed regularly between 2012 and 2022, and routine monitoring of the phytoplankton assemblage likewise indicated differences in the phytoplankton community composition upstream and downstream of the weir. The upstream section was characterised by various eukaryotic algae; in contrast, frequent and intensive cyanobacteria blooms occurred in the downstream section. Multivariate analyses showed a correlation between the different phytoplankton assemblages and physico-chemical properties of the river water. Many freshwater cyanobacteria and algae taxa are problematic: Microcystis and Dolichospermum produce potent cyanotoxins; flagellated green algae, cryptomonads and dinoflagellates produce substances that cause bad tastes and odours, plus the cells can cause floc disruption during drinking water treatment processes; and certain filamentous green algae and diatoms are known for clogging filters.

Preparation and Characterization of Silver Nanoparticle Cross-linked Polymeric Cages by Freshwater Cyanobacteria and their Bactericidal Evaluation against Multi-Drug Resistant Bacteria

Abstract: Introduction: Over the past 60 years, numerous modern types of antibiotics have been developed. Antibiotic overuse has been largely responsible for spreading resistant strains that endangering the public's health at an alarming rate. It prompted the pacing advert of new resistance mechanisms and a lessening in the productivity of treating common infectious. Objectives: The present study emphasizes using cyanobacteria silver nanoparticle conjugates (Ag-NPCs) as a drug delivery system to predominantly control Multi-Drug Resistant bacteria. Materials and Methods: The Ag-NPCs were prepared using a sodium alginate calcium chloride cross-linking process. The Ag-NPCs properties have been characterized by UV-vis-Spectroscopy, FTIR (Fourier Transform Infrared Spectroscopy), Transmission Electron Microscopy (TEM), EDAX (Energy Dispersive Analysis X-Ray), and Scanning Electron Microscopic analysis (SEM) analysis. Results: The SEM and TEM analysis showed that Ag-NPCs have been bio-reduced to the size of 20-22nm that are trapped on the surface. FTIR analysis and EDAX analysis are used to confirm the bio-reduction of Ag-NPCs. The antibacterial activity of Ag-NPCs showed prominent results against four MDR bacteria by exhibiting a zone of inhibition with a range of 2-10 mm. Keywords: Cyanobacteria, Multi-Drug Resistant bacteria, Cyanobacteria Silver nanoparticle conjugates, Drug delivery system, Antibacterial activity.

Synchrotron-based X-ray fluorescence microscopy mapping the ionome of a toxic freshwater cyanobacterium

Harmful algal blooms (HABs) pose a major environmental concern across the globe. In abundance, cyanobacteria, or so-called green-blue algae can produce extremely dangerous cyanotoxins that harm humans and animals. This study focused on the mapping and distribution of intracellular macro-and micronutrients of the wide-spread freshwater cyanobacteria Microcystis aeruginosa (M. aeruginosa). Towards a better understanding of trace metal uptake and homeostasis throughout the cell cycle, we quantitatively mapped the spatial distribution of the elements P, K, Fe, Ca, Zn, Mn, and Cu across the ultrastructure of frozen-hydrated single cells using state-of-the-art X-ray nanofluorescence imaging at the Advanced Photon Source (APS) at Argonne National Laboratory. Bulk cellular nutrient and trace metal content correlated well with the total intracellular elemental content in individual cells obtained by quantitative synchrotron X-ray fluorescence measurements. Multi-dimensional mappings showed P and K atoms colocalized as discrete semicircular hotspots that were analyzed with respect to their stoichiometry. Elevated Cu and Ca concentrations were detected along division plane of cells. P and K were found to have similar spatial elemental distribution with about 65% and 69% of the total cellular P and K, respectively, located at the hotspots. The P and K colocalization were refined further using nanotomography, showing a K envelope surrounding the P core. Inorganic P and organic P compounds were specified using solution-state 31P nuclear magnetic resonance (NMR) spectroscopy from M. aeruginosa. Of the total extracted P determined by 31P NMR spectroscopy, 47% were found to be nucleotides while only 11% were polyphosphates. Multimodal X-ray imaging provides a better understanding of intracellular biochemical processes in cyanobacteria, helping us monitor and combat an emerging environmental threat.

Plastoquinone Lipids: Their Synthesis via a Bifunctional Gene and Physiological Function in a Euryhaline Cyanobacterium, Synechococcus sp. PCC 7002

Eukaryotic photosynthetic organisms synthesize triacylglycerols, which are crucial physiologically as major carbon and energy storage compounds and commercially as food oils and raw materials for carbon-neutral biofuel production. TLC analysis has revealed triacylglycerols are present in several cyanobacteria. However, mass spectrometric analysis has shown that freshwater cyanobacterium, Synechocystis sp. PCC 6803, contains plastoquinone-B and acyl plastoquinol with triacylglycerol-like TLC mobility, concomitantly with the absence of triacylglycerol. Synechocystis contains slr2103, which is responsible for the bifunctional synthesis of plastoquinone-B and acyl plastoquinol and also for NaCl-stress acclimatizing cell growth. However, information is limited on the taxonomical distribution of these plastoquinone lipids, and their synthesis genes and physiological roles in cyanobacteria. In this study, a euryhaline cyanobacterium, Synechococcus sp. PCC 7002, shows the same plastoquinone lipids as those in Synechocystis, although the levels are much lower than in Synechocystis, triacylglycerol being absent. Furthermore, through an analysis of a disruptant to the homolog of slr2103 in Synechococcus, it is found that the slr2103 homolog in Synechococcus, similar to slr2103 in Synechocystis, contributes bifunctionally to the synthesis of plastoquinone-B and acyl plastoquinol; however, the extent of the contribution of the homolog gene to NaCl acclimatization is smaller than that of slr2103 in Synechocystis. These observations suggest strain- or ecoregion-dependent development of the physiological roles of plastoquinone lipids in cyanobacteria and show the necessity to re-evaluate previously identified cyanobacterial triacylglycerol through TLC analysis with mass spectrometric techniques.

Characterization of a novel thermophilic cyanobacterium within Trichocoleusaceae, Trichothermofontia sichuanensis gen. et sp. nov., and its CO2-concentrating mechanism.

Thermophiles from extreme thermal environments have shown tremendous potential regarding ecological and biotechnological applications. Nevertheless, thermophilic cyanobacteria remain largely untapped and are rarely characterized. Herein, a polyphasic approach was used to characterize a thermophilic strain, PKUAC-SCTB231 (hereafter B231), isolated from a hot spring (pH 6.62, 55.5°C) in Zhonggu village, China. The analyses of 16S rRNA phylogeny, secondary structures of 16S-23S ITS and morphology strongly supported strain B231 as a novel genus within Trichocoleusaceae. Phylogenomic inference and three genome-based indices further verified the genus delineation. Based on the botanical code, the isolate is herein delineated as Trichothermofontia sichuanensis gen. et sp. nov., a genus closely related to a validly described genus Trichocoleus. In addition, our results suggest that Pinocchia currently classified to belong to the family Leptolyngbyaceae may require revision and assignment to the family Trichocoleusaceae. Furthermore, the complete genome of Trichothermofontia B231 facilitated the elucidation of the genetic basis regarding genes related to its carbon-concentrating mechanism (CCM). The strain belongs to β-cyanobacteria according to its β-carboxysome shell protein and 1B form of Ribulose bisphosphate Carboxylase-Oxygenase (RubisCO). Compared to other thermophilic strains, strain B231contains a relatively low diversity of bicarbonate transporters (only BicA for HCO3- transport) but a higher abundance of different types of carbonic anhydrase (CA), β-CA (ccaA) and γ-CA (ccmM). The BCT1 transporter consistently possessed by freshwater cyanobacteria was absent in strain B231. Similar situation was occasionally observed in freshwater thermal Thermoleptolyngbya and Thermosynechococcus strains. Moreover, strain B231 shows a similar composition of carboxysome shell proteins (ccmK1-4, ccmL, -M, -N, -O, and -P) to mesophilic cyanobacteria, the diversity of which was higher than many thermophilic strains lacking at least one of the four ccmK genes. The genomic distribution of CCM-related genes suggests that the expression of some components is regulated as an operon and others in an independently controlled satellite locus. The current study also offers fundamental information for future taxogenomics, ecogenomics and geogenomic studies on distribution and significance of thermophilic cyanobacteria in the global ecosystem.

Biocidal H2O2 treatment emphasizes the crucial role of cyanobacterial extracellular polysaccharides against external strong oxidative stress.

A biocidal level of hydrogen peroxide (H2O2), far beyond the natural level, is widely used to control bloom-forming cyanobacteria in freshwater. The extracellular polymeric substance of these cyanobacteria is a key factor in determining the applied H2O2 dosage. The exopolysaccharide (EPS) in the extracellular polymer shows H2O2 scavenging capability. However, the scavenging capabilities of EPSs from other cyanobacteria against biocidal levels of H2O2 as well as their protective roles against cyanobacterial cells are not well known. In this study, we used four nonbloom-forming cyanobacteria as target organisms, two with rich EPS envelopes (EPS-rich strains) and two with thin EPS envelopes (EPS-thin strains), to assess the roles of EPS. It was found that the two EPS-rich strains were much more tolerant to a high dose of exogenous H2O2 than the two EPS-thin strains. The EPSs extracted from the four strains exhibited similar but rapid H2O2 scavenging activity. Additionally, the EPSs from the EPS-rich strains could improve the tolerance of the EPS-thin strains to H2O2 stress, implying potentially nonselective protection against oxidative stress. In addition, all the cell lysates of the four strains showed H2O2 decomposition ability, with the efficiency being slightly different between the two types of strains. This study suggests that cyanobacterial EPS plays a generally crucial role against external strong oxidative stress and may provide a useful reference for the application of H2O2 in environmental management.

Assessment and Selection of Cyanobacterial Strains for CO2 Mineral Sequestration: Implications for Carbonation Mechanism

CO2 mineral carbonation induced by microalgae is an emerging approach to carbon capture, utilization, and storage (CCUS). Freshwater cyanobacteria are common microalgae in nature that can raise the pH of eutrophic waters and drive the precipitation of carbonate. Still, limited studies have been conducted to evaluate and select appropriate cyanobacteria strains for CCUS. Here we present experimental investigations to compare the capacity of different freshwater cyanobacterial strains in converting CO2 to carbonates. We compare five cyanobacterial strains by monitoring their growth curves. We examine three metrics, the maximum pH of the solution, hydroxide production capacity, and extracellular polymeric substances (EPS) secretion capacity, to assess the capacity for carbon sequestration. Our results indicate that among the five strains, Microcystis aeruginosa shows the highest pH and EPS content per unit cell number, marking the most significant capacity for CO2 carbonation. We observe carbonate precipitates as hydromagnesite and dypingite. We suggest the negatively charged, hydrophilic EPS can effectively promote the precipitation of magnesium carbonate and inhibit the precipitation of calcium carbonate. Overall, our approach provides a framework for assessing and selecting cyanobacterial strains for CO2 carbonation, advancing the understanding of the mechanism of microalgae-induced CO2 Mg-carbonation from the perspective of EPS surface properties.

Freshwater Salinization Impacts the Interspecific Competition between Microcystis and Scenedesmus

Freshwater salinization is a growing environmental issue caused by various anthropic or natural factors that lead to changes in water chemistry and physical conditions, affecting the survival and diversity of phytoplankton. In this study, we tested the physiological, morphological and interspecific competition of the freshwater cyanobacterium Microcystis aeruginosa and the green algae Scenedesmus obliquus to salinity stress. Results demonstrated that increasing salinity had a significant negative effect on the growth of M. aeruginosa and S. obliquus. M. aeruginosa showed a decline in growth rate with increasing salinity, while S. obliquus showed a lower growth rate under salinity stress but with no significant difference between the two salinity groups. In cocultures, S. obliquus outcompeted M. aeruginosa, and the displacement was accelerated with increasing salinity. The photosynthetic performance of both algae was affected by salinity, the presence of competitors, and the cultivation time. S. obliquus showed morphological variations under salinity stress and the presence of a competitor. The study suggests that salinity stress and competition can have a significant impact on the growth and performance of algae species. The findings of our study suggest that the salinization of freshwater can impact the interspecific interactions among phytoplankton, which play a crucial role in the functioning of freshwater ecosystems.

Toxicological effects of cyanobacterial metabolites on zebrafish larval development

Freshwater cyanobacteria are known worldwide for their potential to produce toxins. However, these organisms are also found in marine, terrestrial and extreme environments and produce unique compounds, other than toxins. Nevertheless, their effects on biological systems are still barely known. This work tested extracts of different cyanobacterial strains against zebrafish (Danio rerio) larvae and analyzed their metabolomic profiles using liquid chromatography combined with mass spectrometry. Strains Desertifilum tharense, Anagnostidinema amphibium, and Nostoc sp. promoted morphological abnormalities such as pericardial edema, edema in the digestive system region, curvature of the tail and spine in zebrafish larvae in vivo. In contrast, Microcystis aeruginosa and Chlorogloeopsis sp. did not promote such changes. Metabolomics revealed unique compounds belonging to the classes of terpenoids, peptides, and linear lipopeptides/microginins in the nontoxic strains. The toxic strains were shown to contain unique compounds belonging to the classes of cyclic peptides, amino acids and other peptides, anabaenopeptins, lipopeptides, terpenoids, and alkaloids and derivatives. Other unknown compounds were also detected, highlighting the rich structural diversity of secondary metabolites produced by cyanobacteria. The effects of cyanobacterial metabolites on living organisms, mainly those related to potential human and ecotoxicological risks, are still poorly known. This work highlights the diverse, complex, and unique metabolomic profiles of cyanobacteria and the biotechnological potential and associated risks of exposure to their metabolites.