Synechococcus Sp Research Articles

Allelopathic activity of cyanobacteria isolated from Lake Tuzkol.

Allelopathy plays a crucial role in shaping phytoplankton community dynamics and diversity. It influences competition between photoautotrophs for resources and affects species succession in aquatic ecosystems. This article evaluates the allelopathic activity of cyanobacteria isolated from Lake Tuzkol, Kazakhstan. The allelopathic effects, including growth inhibition or stimulation, were assessed by adding cell-free filtrates of the cyanobacteria Oscillatoria sp. SS-9, Nostoc sp. CZS 2205, Synechococcus sp. SS-5, or Anabaena sp. SS-8 to the tested microalgae. The most pronounced effect was observed with Nostoc sp. CZS 2205, which reduced the cell counts of Chlorella vulgaris SP BB-2 and Chlamydomonas reinhardtii CC-124 by 60% and 57%, respectively, and Scenedesmus quadricauda CC-1 and Ankistrodesmus falcatus CB-2 by 55% and 53%, respectively. Synechococcus sp. SS-5, in contrast, stimulated the growth of Chlorella vulgaris SP BB-2 and Scenedesmus quadricauda CC-1 by 11% and 8.8%, respectively. Filtrates from Oscillatoria sp. SS-9 and Anabaena sp. SS-8 had no significant impact on microalgal growth. Considering the significant allelopathic activity of Nostoc sp. CZS 2205, an agar diffusion test using biomass extracts confirmed a significant inhibitory effect, with the biomass extracts showing stronger activity than cell-free filtrates. A detailed analysis of the cell-free filtrates revealed eight compounds, including methyl heptadecanoate, methyl eicosanoate, tricosane, methyl octadeca-9,12-dienoate, methyl 13,16-octadecadienoate, and 2,2-dimethoxybutane. Additionally, nostocyclamide, a cyclic peptide, was identified in the biomass extract. The detection of nostocyclamide emphasizes its ecological importance and potential evolutionary role. These results enhance our understanding of the role of cyanobacteria in aquatic ecosystems and lay the groundwork for future research into their ecological applications.

Synthesis of N-Sulfopropylated Hyperbranched Polyethyleneimine with Enhanced Biocompatibility and Antimicrobial Activity.

Hyperbranched polyethyleneimine having 25,000 Da molecular weight was functionalized by a simple sulfopropylation reaction, affording a novel N-sulfopropylated PEI derivative (PEI-SO3 -). The successful introduction of N-sulfopropyl and sulfobetaine groups to the amino groups of PEI was spectroscopically confirmed. Furthermore, the antibacterial and anti-cyanobacterial activity of PEI-SO3 - in comparison to the parent PEI were investigated on two type heterotrophic bacteria, i. e., Gram (-) Escherichia coli and Gram (+) Staphylococcus Aureus bacteria, and one type of autotrophic cyanobacterium, i. e. Synechococcus sp. PCC 7942. Both PEI-SO3 - and PEI showed an enhanced, concentration-dependent antibacterial and anti-cyanobacterial activity against the tested bacteria strains, with PEI-SO3 - exhibiting higher activity than the parent PEI, signifying that the introduction of the sulfopropyl and sulfobetaine groups to the PEI amino groups enhanced the antibacterial and the anti-cyanobacterial properties of PEI. In the case of cyanobacteria, PEI-SO3 - was found to affect the integrity of the photosynthetic system by the inhibition of Photosystem-II electron transport activity. Cytocompatibility and hemocompatibility studies revealed that PEI-SO3 - exhibits high biocompatibility, suggesting that PEI-SO3 - could be considered as an attractive antibacterial and anti-cyanobacterial candidate for various applications in the disinfection industry and also against the harmful cyanobacterial blooms.

Isolation, Identification and Pigment Analysis of Novel Cyanobacterial Strains from Thermal Springs.

Cyanobacterial pigments have attracted considerable attention in industry due to their bioactive potential and natural origin. In the present study, the growth dynamics and pigment composition, in terms of chlorophyll a, total carotenoids and phycobiliprotein content, of four cyanobacterial strains isolated from thermal springs, namely Oscillatoria subbrevis CZS 2201, Phormidium ambiguum CZS 2205, Nostoc calcicola TSZ 2203, and Synechococcus sp. CZS 2204, were investigated. The analysis revealed that the maximum quantity of chlorophyll a and total carotenoids was observed in Oscillatoria subbrevis CZS 2201 (26.49 and 3.44 µg mL-1), followed by Phormidium ambiguum CZS 2205 (18.64 and 2.32 µg mL-1), whereas a minimum amount was detected in Synechococcus sp. CZS 2204 (12.13 and 1.24 µg mL-1), respectively. In addition, Oscillatoria subbrevis CZS 2201 showed higher quantity of phycobiliproteins, especially C-phycocyanin (45.81 mg g-1), C-phycoerythrin (64.17 mg g-1) and C-allophycocyanin (27.45 mg g-1). Moreover, carotenoid derivatives of Oscillatoria subbrevis CZS 2201 were also identified, among which β-carotene was the dominant form (1.94 µg mL-1), while the accumulation of zeaxanthin and myxoxanthophyll was relatively high (0.53 and 0.41 µg mL-1, respectively) compared with echinenone and cryptoxanthin (0.34 and 0.23 µg mL-1, respectively). The study revealed that Oscillatoria subbrevis CZS 2201 was a potent producer of secondary carotenoids, including myxoxanthophyll.

Pioneering precision in markerless strain development for Synechococcus sp. PCC 7002

Marine cyanobacteria such as Picosynechococcus sp. (formerly called Synechococcus sp.) PCC 7002 are promising chassis for photosynthetic production of commodity chemicals with low environmental burdens. Genetic engineering of cyanobacteria conventionally employs antibiotic resistance markers. However, limited availability of antibiotic-resistant markers is a problem for highly multigenic strain engineering. Although several markerless genetic manipulation methods have been developed for PCC 7002, they often lack versatility due to the requirement of gene disruption in the host strain. To achieve markerless transformation in Synechococcus sp. with no requirements for the host strain, this study developed a method in which temporarily introduces a mutated phenylalanyl-tRNA synthetase gene (pheS) into the genome for counter selection. Amino acid substitutions in the PheS that cause high susceptibility of PCC 7002 to the phenylalanine analog p-chlorophenylalanine were examined, and the combination of T261A and A303G was determined as the most suitable mutation. The mutated PheS-based selection was utilized for the markerless knockout of the nblA gene in PCC 7002. In addition, the genetic construct containing the lldD and lldP genes from Escherichia coli was introduced into the ldhA gene site using the counter selection strategy, resulting in a markerless recombinant strain. The repeatability of this method was demonstrated by the double markerless knockin recombinant strain, suggesting it will be a powerful tool for multigenic strain engineering of cyanobacteria.

In Vivo Biocompatibility of Synechococcus sp. PCC 7002-Integrated Scaffolds for Skin Regeneration.

Cyanobacteria, commonly known as blue-green algae, are prevalent in freshwater systems and have gained interest for their potential in medical applications, particularly in skin regeneration. Among these, Synechococcus sp. strain PCC 7002 stands out because of its rapid proliferation and capacity to be genetically modified to produce growth factors. This study investigates the safety of Synechococcus sp. PCC 7002 when used in scaffolds for skin regeneration, focusing on systemic inflammatory responses in a murine model. We evaluated the following three groups: scaffolds colonized with genetically engineered bacteria producing hyaluronic acid, scaffolds with wild-type bacteria, and control scaffolds without bacteria. After seven days, we assessed systemic inflammation by measuring changes in cytokine profiles and lymphatic organ sizes. The results showed no significant differences in spleen, thymus, and lymph node weights, indicating a lack of overt systemic toxicity. Blood cytokine analysis revealed elevated levels of IL-6 and IL-1β in scaffolds with bacteria, suggesting a systemic inflammatory response, while TNF-α levels remained unaffected. Proteome profiling identified distinct cytokine patterns associated with bacterial colonization, including elevated inflammatory proteins and products, indicative of acute inflammation. Conversely, control scaffolds exhibited protein profiles suggestive of a rejection response, characterized by increased levels of cytokines involved in T and B cell activation. Our findings suggest that Synechococcus sp. PCC 7002 does not appear to cause significant systemic toxicity, supporting its potential use in biomedical applications. Further research is necessary to explore the long-term effects and clinical implications of these responses.

Production and utilization of pseudocobalamin in marine Synechococcus cultures and communities.

Cobalamin influences marine microbial communities because an exogenous source is required by most eukaryotic phytoplankton, and demand can exceed supply. Pseudocobalamin is a cobalamin analogue produced and used by most cyanobacteria but is not directly available to eukaryotic phytoplankton. Some microbes can remodel pseudocobalamin into cobalamin, but a scarcity of pseudocobalamin measurements impedes our ability to evaluate its importance for marine cobalamin production. Here, we perform simultaneous measurements of pseudocobalamin and methionine synthase (MetH), the key protein that uses it as a co-factor, in Synechococcus cultures and communities. In Synechococcus sp. WH8102, pseudocobalamin quota decreases in low temperature (17°C) and low nitrogen to phosphorus ratio, while MetH did not. Pseudocobalamin and MetH quotas were influenced by culture methods and growth phase. Despite the variability present in cultures, we found a comparably consistent quota of 300 ± 100 pseudocobalamin molecules per cyanobacterial cell in the Northwest Atlantic Ocean, suggesting that cyanobacterial cell counts may be sufficient to estimate pseudocobalamin inventories in this region. This work offers insights into cellular pseudocobalamin metabolism, environmental and physiological conditions that may influence it, and provides environmental measurements to further our understanding of when and how pseudocobalamin can influence marine microbial communities.

Genome-Scale Metabolic Model Reconstruction and Investigation into the Fluxome of the Fast-Growing Cyanobacterium Synechococcus sp. PCC 11901.

The ability to convert atmospheric CO2 and light into biomass and value-added chemicals makes cyanobacteria a promising resource microbial host for biotechnological applications. A newly discovered fastest-growing cyanobacterial strain, Synechococcus sp. PCC 11901, has been reported to have the highest biomass accumulation rate, making it a preferred target host for producing renewable fuels, value-added biochemicals, and natural products. System-level knowledge of an organism is imperative to understand the metabolic potential of the strain, which can be attained by developing genome-scale metabolic models (GEMs). We present the first genome-scale metabolic model of Synechococcus sp. PCC 11901 (iRS840), which contains 840 genes, 1001 reactions, and 944 metabolites. The model has been optimized and validated under different trophic modes, i.e., autotrophic and mixotrophic, by conducting an in vivo growth experiment. The robustness of the metabolic network was evaluated by changing the biomass coefficient of the model, which showed a higher sensitivity toward pigments under the photoautotrophic condition, whereas under the heterotrophic condition, amino acids were found to be more influential. Furthermore, it was discovered that PCC 11901 synthesizes succinyl-CoA via succinic semialdehyde due to its imperfect TCA cycle. Subsequent flux balance analysis (FBA) revealed a quantum yield of 0.16 in silico, which is higher compared to that of PCC 6803. Under mixotrophic conditions (with glycerol and carbon dioxide), the flux through the Calvin cycle increased compared to autotrophic conditions. This model will be useful for gaining insights into the metabolic potential of PCC 11901 and developing effective metabolic engineering strategies for product development.

Molecular Characterization of the MoxR AAA+ ATPase of Synechococcus sp. Strain NKBG15041c.

We isolated a stress-tolerance-related gene from a genome library of Synechococcus sp. NKBG15041c. The expression of the gene in E. coli confers resistance against various stresses. The gene encodes a MoxR AAA+ ATPase, which was designated SyMRP since it belongs to the MRP subfamily. The recombinant SyMRP showed weak ATPase activity and protected citrate synthase from thermal aggregation. Interestingly, the chaperone activity of SyMRP is ATP-dependent. SyMRP exists as a stable hexamer, and ATP-dependent conformation changes were not detected via analytical ultracentrifugation (AUC) or small-angle X-ray scattering (SAXS). Although the hexameric structure predicted by AlphaFold 3 was the canonical flat-ring structure, the structures observed by atomic force microscopy (AFM) and transmission electron microscopy (TEM) were not the canonical ring structure. In addition, the experimental SAXS profiles did not show a peak that should exist in the symmetric-ring structure. Therefore, SyMRP seems to form a hexameric structure different from the canonical hexameric structure of AAA+ ATPase.

Repurposing endogenous Type I-D CRISPR-Cas system for genome editing in Synechococcus sp. PCC7002

Synechococcus sp. PCC7002 has been considered as a photosynthetic chassis for the conversion of CO2 into biochemicals through genetic modification. However, conventional genetic manipulation techniques prove inadequate for comprehensive genetic modifications in this strain. Here, we present the development of a genome editing tool tailored for S. PCC7002, leveraging its endogenous type I-D CRISPR-Cas system. Utilizing this novel tool, we successfully deleted the glgA1 gene and iteratively edited the genome to obtain a double mutant of glgA1 and glgA2 genes. Additionally, large DNA fragments encompassing the entire type I-A (∼14 kb) or III-B CRISPR-Cas (∼21 kb) systems were completely knocked-out in S. PCC7002 using our tool. Furthermore, the endogenous pAQ5 plasmid, approximately 38 kb in length, was successfully cured from S. PCC7002. Our work demonstrates the feasibility of harnessing the endogenous CRISPR-Cas system for genome editing in S. PCC7002, thereby enriching the genetic toolkit for this species and providing a foundation for future enhancements in its biosynthetic efficiency.

16S rRNA-based Metagenomic Analysis of Beeswax-coated Saba Banana (Musa × paradisiaca) Pseudostem

Bananas are one of the most popular fruits, and their production generates significant agricultural waste. Banana pseudostems, a by-product of the banana industry, are being investigated as a renewable and biodegradable alternative to synthetic food packaging materials. However, these pseudostems have the potential to harbor harmful bacteria due to their natural fiber composition. Therefore, this study analyzes the effect of beeswax coating on the microbial communities in banana pseudostems. The microbial community is analyzed through a metagenomics approach that targets the 16S rRNA gene of the Saba banana (Musa × paradisiaca) pseudostem. Two experimental conditions were considered: pseudostem with beeswax coating and pseudostem without beeswax coating. The findings indicate that the microbial communities in all samples are primarily composed of the phyla Proteobacteria, Cyanobacteria, and Firmicutes. The dominant species found in uncoated banana pseudostem is Pantoea sp. At-9b, Escherichia coli, Synechococcus sp. JA-3-3-Ab, Pantoea vagans, and Klebsiella pneumoniae. The dominant species found in beeswax-coated banana pseudostem is Synechococcus sp. JA-3-3-Ab, Pseudanabaena sp. PCC 7367, Chroococcidiopsis thermalis, Priestia megaterium, and Ammonifex degensii. The Chao1, Shannon, Simpson, and Equitability indices indicate that the species richness, diversity, and evenness in the uncoated banana pseudostem are higher than in the beeswax-coated banana pseudostem. The degree of similarity between bacterial populations found in uncoated banana pseudostem and beeswax-coated banana pseudostem is around 53.9%.

A serum-free culture medium production system by co-culture combining growth factor-secreting cells and l-lactate-assimilating cyanobacteria for sustainable cultured meat production

Large-scale production of cultured meat requires bulk culture medium containing growth-promoting proteins from animal serum. However, animal serum for mammalian cell culture is associated with high costs, ethical concerns, and contamination risks. Owing to its growth factor content, conditioned medium from rat liver epithelial RL34 cells can replace animal serum for myoblast proliferation. More seeded cells and longer culture periods are thought to yield higher growth factor levels, resulting in more effective muscle cell proliferation. However, RL34 cells can deplete nutrients and release harmful metabolites into the culture medium over time, potentially causing growth inhibition and apoptosis. This issue highlights the need for waste clearance during condition medium production. To address this issue, we introduced a lactate permease gene (lldP) and an l-lactate-to-pyruvate conversion enzyme gene (lldD) to generate a recombinant l-lactate-assimilating cyanobacterium Synechococcus sp. KC0110 strain. Transwell co-culture of this strain with RL34 cells exhibited a marked reduction in the levels of harmful metabolites, lactate and ammonium, while maintaining higher concentrations of glucose, pyruvate, and pyruvate-derived amino acids than those seen with RL34 cell monocultures. The co-culture medium supported myoblast proliferation without medium dilution or additional nutrients, which was attributed to the waste clearance and nutrient replenishment effects of the KC0110 strain. This culture system holds potential for the production of low-cost, and animal-free cultured meat.

Molecular mechanism of a coastal cyanobacterium Synechococcus sp. PCC 7002 adapting to changing phosphate concentrations

Phosphorus concentration on the surface of seawater varies greatly with different environments, especially in coastal. The molecular mechanism by which cyanobacteria adapt to fluctuating phosphorus bioavailability is still unclear. In this study, transcriptomes and gene knockouts were used to investigate the adaptive molecular mechanism of a model coastal cyanobacterium Synechococcus sp. PCC 7002 during periods of phosphorus starvation and phosphorus recovery (adding sufficient phosphorus after phosphorus starvation). The findings indicated that phosphorus deficiency affected the photosynthesis, ribosome synthesis, and bacterial motility pathways, which recommenced after phosphorus was resupplied. Even more, most of the metabolic pathways of cyanobacteria were enhanced after phosphorus recovery compared to the control which was kept in continuous phosphorus replete conditions. Based on transcriptome, 54 genes potentially related to phosphorus-deficiency adaptation were selected and knocked out individually or in combination. It was found that five mutants showed weak growth phenotype under phosphorus deficiency, indicating the importance of the genes (A0076, A0549-50, A1094, A1320, A1895) in the adaptation of phosphorus deficiency. Three mutants were found to grow better than the wild type under phosphorus deficiency, suggesting that the products of these genes (A0079, A0340, A2284–86) might influence the adaptation to phosphorus deficiency. Bioinformatics analysis revealed that cyanobacteria exposed to highly fluctuating phosphorus concentrations have more sophisticated phosphorus acquisition strategies. These results elucidated that Synechococcus sp. PCC 7002 have variable phosphorus response mechanisms to adapt to fluctuating phosphorus concentration, providing a novel perspective of how cyanobacteria may respond to the complex and dynamic environments.

Experimental evidence that nitrogen-fixing cyanobacterium Trichodesmium spp. supplies new nitrogen source to marine phytoplankton

In oligotrophic oceans, primary productivity is widely limited by nitrogen bioavailability. The broadly distributed and abundant nitrogen-fixing cyanobacterium Trichodesmium plays an important role in the oceanic nitrogen and carbon cycles by providing a “new” source of nitrogen to many non-diazotrophic microbes, thereby driving new primary production in the ocean. However, the underlying process and mechanism of nitrogen supply from Trichodesmium to other phytoplankton remain unclear. Here, our results demonstrated that the fixed nitrogen released by Trichodesmium could sustain the growth of a non-nitrogen-fixing cyanobacterium Synechococcus sp. PCC 7002, including a mutant strain (Mut-ureA) that cannot use urea. However, the growth rate of Mut-ureA was approximately 20% lower than that of the wild strain when Trichodesmium filtrate was used for nitrogen supply. This result was consistent with the composition of the Trichodesmium exudate, in which urea comprised more than 20% of the total fixed nitrogen that was released. It is evident from the experiments that a fraction of the Trichodesmium-derived nitrogen was not available to Mut-ureA. Our results suggested that Trichodesmium produces dissolved organic nitrogen, especially a certain amount of urea as a “new” nitrogen source, benefiting in particular populations of surrounding phytoplankton species.

Elucidating the role of primary and secondary sphere Zn2+ ligands in the cyanobacterial CO2 uptake complex NDH-14: The essentiality of arginine in zinc coordination and catalysis

Inorganic carbon uptake in cyanobacteria is facilitated by an energetically intensive CO2-concentrating mechanism (CCM). Specialized Type-1 NDH complexes function as a part of this mechanism to couple photosynthetic energy generated by redox reactions of the electron transport chain (ETC) to CO2 hydration. This active site of CO2 hydration incorporates an arginine side chain as a Zn ligand, diverging from the typical histidine and/or cysteine residues found in standard CAs. In this study, we focused on mutating three amino acids in the active site of the constitutively expressed NDH-14 CO2 hydration complex in Synechococcus sp. PCC7942: CupB-R91, which acts as a zinc ligand, and CupB-E95 and CupB-H89, both of which closely interact with the arginine ligand. These mutations aimed to explore how they affect the unusual metal ligation by CupB-R91 and potentially influence the unusual catalytic process. The most severe defects in activity among the targeted residues are due to a substitution of CupB-R91 and the ionically interacting E95 since both proved essential for the structural stability of the CupB protein. On the other hand, CupB-H89 mutations show a range of catalytic phenotypes indicating a role of this residue in the catalytic mechanism of CO2-hydration, but no evidence was obtained for aberrant carbonic anhydrase activity that would have indicated uncoupling of the CO2-hydration activity from proton pumping. The results are discussed in terms of possible alternative CO2 hydration mechanisms.

Synechococcus sp. PCC7335 responses to far-red enriched spectra and anoxic/microoxic atmospheres: Potential for astrobiotechnological applications

Recently, cyanobacteria have gained attention in space exploration to support long-term crewed missions via Bioregenerative Life Support Systems. In this frame, cyanobacteria would provide biomass and profitable biomolecules through oxygenic photosynthesis, uptaking CO2, and releasing breathable O2. Their growth potential and organic matter production will depend on their ability to photoacclimate to different light intensities and spectra, maximizing incident light harvesting. Studying cyanobacteria responses to different light regimes will also benefit the broader field of astrobiology, providing data on the possibility of oxygenic photosynthetic life on planets orbiting stars with emission spectra different than the Sun. Here, we tested the acclimation and productivity of Synechococcus sp. PCC7335 (hereafter PCC7335), capable of Far-Red Light Photoacclimation (FaRLiP) and type III chromatic acclimation (CA3), in an anoxic, CO2-enriched atmosphere and under a spectrum simulating the low energetic light regime of an M-dwarf star, also comparable to a subsuperficial environment. When exposed to the light spectrum, with few photons in the visible (VIS) and rich in far-red (FR), PCC7335 did not activate FaRLiP but acclimated only via CA3, achieving a biomass productivity higher than expected, considering the low VIS light availability, and a higher production of phycocyanin, a valuable pigment, with respect to solar light. Its growth or physiological responses of PCC7335 were not affected by the anoxic atmosphere. In these conditions, PCC7335 efficiently produced O2 and scavenged CO2. Results highlight the photosynthetic plasticity of PCC7335, its suitability for astrobiotechnological applications, and the importance to investigate biodiversity of oxygenic photosynthesis for searching life beyond Earth.

A toolbox to engineer the highly productive cyanobacterium Synechococcus sp. PCC 11901.

Synechococcus sp. PCC 11901 (PCC 11901) is a fast-growing marine cyanobacterial strain that has a capacity for sustained biomass accumulation to very high cell densities, comparable to that achieved by commercially relevant heterotrophic organisms. However, genetic tools to engineer PCC 11901 for biotechnology applications are limited. Here we describe a suite of tools based on the CyanoGate MoClo system to unlock the engineering potential of PCC 11901. First, we characterized neutral sites suitable for stable genomic integration that do not affect growth even at high cell densities. Second, we tested a suite of constitutive promoters, terminators, and inducible promoters including a 2,4-diacetylphloroglucinol (DAPG)-inducible PhlF repressor system, which has not previously been demonstrated in cyanobacteria and showed tight regulation and a 228-fold dynamic range of induction. Lastly, we developed a DAPG-inducible dCas9-based CRISPR interference (CRISPRi) system and a modular method to generate markerless mutants using CRISPR-Cas12a. Based on our findings, PCC 11901 is highly responsive to CRISPRi-based repression and showed high efficiencies for single insertion (31% to 81%) and multiplex double insertion (25%) genome editing with Cas12a. We envision that these tools will lay the foundations for the adoption of PCC 11901 as a robust model strain for engineering biology and green biotechnology.

Monitoring of toxic cyanobacterial blooms in Lalla Takerkoust reservoir by satellite imagery and microcystin transfer to surrounding farms

Cyanobacterial harmful algal blooms (CyanoHABs) threaten public health and freshwater ecosystems worldwide. In this study, our main goal was to explore the dynamics of cyanobacterial blooms and how microcystins (MCs) move from the Lalla Takerkoust reservoir to the nearby farms. We used Landsat imagery, molecular analysis, collecting and analyzing physicochemical data, and assessing toxins using HPLC. Our investigation identified two cyanobacterial species responsible for the blooms: Microcystis sp. and Synechococcus sp. Our Microcystis strain produced three MC variants (MC-RR, MC-YR, and MC-LR), with MC-RR exhibiting the highest concentrations in dissolved and intracellular toxins. In contrast, our Synechococcus strain did not produce any detectable toxins. To validate our Normalized Difference Vegetation Index (NDVI) results, we utilized limnological data, including algal cell counts, and quantified MCs in freeze-dried Microcystis bloom samples collected from the reservoir. Our study revealed patterns and trends in cyanobacterial proliferation in the reservoir over 30 years and presented a historical map of the area of cyanobacterial infestation using the NDVI method. The study found that MC-LR accumulates near the water surface due to the buoyancy of Microcystis. The maximum concentration of MC-LR in the reservoir water was 160 µg L−1. In contrast, 4 km downstream of the reservoir, the concentration decreased by a factor of 5.39 to 29.63 µgL−1, indicating a decrease in MC-LR concentration with increasing distance from the bloom source. Similarly, the MC-YR concentration decreased by a factor of 2.98 for the same distance. Interestingly, the MC distribution varied with depth, with MC-LR dominating at the water surface and MC-YR at the reservoir outlet at a water depth of 10 m. Our findings highlight the impact of nutrient concentrations, environmental factors, and transfer processes on bloom dynamics and MC distribution. We emphasize the need for effective management strategies to minimize toxin transfer and ensure public health and safety.

Tobacco aquaporin NtAQP1 and human aquaporin hAQP1 contribute to single cell photosynthesis in Synechococcus.

Aquaporins are H2O-permeable membrane protein pores. However, some aquaporins are also permeable to other substances such as CO2. In higher plants, overexpression of such aquaporins has already led to an enhanced photosynthetic performance due to improved CO2 mesophyll conductance. In this work, we investigated the effects of such aquaporins on unicellular photosynthetically active organisms, specifically cyanobacteria. Overexpression of aquaporins NtAQP1 or hAQP1 that might have a function to improve CO2 membrane permeability lead to increased photosynthesis rates in the cyanobacterium Synechococcus sp. PCC7002 as concluded by the rate of evolved O2. A shift in the Plastoquinone pool state of the cells supports our findings. Water permeable aquaporins without CO2 permeability, such as NtPIP2;1, do not have this effect. We conclude that also in single cell organisms like cyanobacteria, membrane CO2 conductivity could be rate limiting and CO2-porins reduce the respective membrane resistance. We could show that besides the tobacco aquaporin NtAQP1 also the human hAQP1 most likely functions as CO2 diffusion facilitator in the photosynthesis assay.

Microalgae polyphosphate nanoparticles deliver bioavailable calcium against phytate antagonism: Ex vivo and in vivo studies

Biogenic nanoparticles are promising carriers to deliver essential minerals. Here, calcium-enriched polyphosphate nanoparticles (CaPNPs) with a Ca/P molar ratio > 0.5 were produced by Synechococcus sp. PCC 7002 in the growth medium containing 1.08 g/L CaCl2, and had nearly spherical morphologies with a wide size distribution of 5–75 nm and strongly anionic surface properties with an average ζ-potential of –39 mV, according to dynamic light-scattering analysis, transmission and scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The ex-vivo ligated mouse ileal loop assays found that calcium in CaPNPs was readily available to intestinal absorption via both ion channel-mediated and endocytic pathways, specifically invoking macropinocytic internalization, lysosomal degradation, and transcytosis. Rat oral pharmacokinetics revealed that CaPNPs had a calcium bioavailability approximately 100 % relative to that of CaCl2 and more than 1.6 times of that of CaCO3. CaPNPs corrected the retinoic acid-induced increase in serum calcium, phosphorus, and bone-specific alkaline phosphatase, and decrease in serum osteocalcin, bone mineral content/density, and femoral geometric parameters with an efficacy equivalent to CaCl2 and markedly greater than CaCO3. In contrast to CaCl2, CaPNPs possessed desirable resistance against phytate’s antagonistic action on calcium absorption in these ex vivo and in vivo studies. Overall, CaPNPs are attractive as a candidate agent for calcium supplementation, especially to populations on high-phytate diets.

Femtosecond optical studies of the primary charge separation reactions in far-red photosystem II from Synechococcus sp. PCC 7335

Primary processes of light energy conversion by Photosystem II (PSII) were studied using femtosecond broadband pump-probe absorption difference spectroscopy. Transient absorption changes of core complexes isolated from the cyanobacterium Synechococcus sp. PCC 7335 grown under far-red light (FRL-PSII) were compared with the canonical Chl a containing spinach PSII core complexes upon excitation into the red edge of the Qy band. Absorption changes of FRL-PSII were monitored at 278 K in the 400–800 nm spectral range on a timescale of 0.1–500 ps upon selective excitation at 740 nm of four chlorophyll (Chl) f molecules in the light harvesting antenna, or of one Chl d molecule at the ChlD1 position in the reaction center (RC) upon pumping at 710 nm. Numerical analysis of absorption changes and assessment of the energy levels of the presumed ion-radical states made it possible to identify PD1+ChlD1− as the predominant primary charge-separated radical pair, the formation of which upon selective excitation of Chl d has an apparent time of ∼1.6 ps. Electron transfer to the secondary acceptor pheophytin PheoD1 has an apparent time of ∼7 ps with a variety of excitation wavelengths. The energy redistribution between Chl a and Chl f in the antenna occurs within 1 ps, whereas the energy migration from Chl f to the RC occurs mostly with lifetimes of 60 and 400 ps. Potentiometric analysis suggests that in canonical PSII, PD1+ChlD1− can be partially formed from the excited (PD1ChlD1)* state.