ABSTRACT Cyanobacteria are an ancient and diverse group of oxyphototrophic bacteria found across a wide range of environments. The taxonomic diversity of terrestrial cyanobacteria inhabiting rock surfaces remains poorly studied despite their key role as pioneering species in ecological succession. We isolated two phycoerythrin-rich strains resembling the genus Leptolyngbya in a survey of filamentous cyanobacteria from previously unstudied epilithic habitats on the Suomenlinna Fortress (UNESCO World Heritage site) in Finland. We employed a comprehensive polyphasic approach to characterize these isolates to account for the known polyphyletic nature of Leptolyngbya and the presence of cryptic taxa. Our analyses revealed that the two strains form a distinct and well-supported clade within the family Leptolyngbyaceae. Therefore, we propose a new monospecific genus, Sivoneniella, following the International Code of Nomenclature for Algae, Fungi, and Plants. Secondary structures of conserved 16S–23S ITS regions (D1–D1’, box B and V3 helices), ITS per cent dissimilarity, multi-locus phylogenies (16S rRNA, rbcLX, rpoC1), and genome-based phylogenomic analyses all support the recognition of this novel cryptic genus. Genome mining and LC-MS analyses revealed the absence of known cyanotoxins in both strains (UHCC 1019T and UHCC 1020), and their cell extracts exhibited no inhibitory effects on the growth of relevant pathogenic bacteria and fungi. These findings advance our understanding of cyanobacterial diversity in terrestrial ecosystems, support the establishment of Sivoneniella as a new genus within the order Leptolyngbyales and explore the biotechnological potential of phycoerythrin-rich strains of S. epilithica.

Filamentous cyanobacterium Spirulina platensis mediates phosphate biomineralization for efficient fluoride immobilization and drives metabolic shift toward stress resistance and biomineralization.

Microbiologically induced calcium carbonate precipitation (MICP) is an ecologically vital process where the metabolic activity of microorganisms causes the precipitation of calcium carbonate. In cyanobacteria, MICP is thought to occur primarily due to photosynthesis. During this process, cyanobacteria consume carbon dioxide, raising the local pH, which leads to conditions favorable to calcium carbonate precipitation. However, how individual cells contribute to MICP is poorly understood. Here, we use quantitative microscopy to obtain direct evidence of MICP caused by the filamentous cyanobacterium Anabaena sp. ATCC 33047 (hereafter Anabaena) in nitrogen fixing conditions. Anabaena cells differentiate into photosynthetic vegetative cells and nitrogen-fixing heterocysts. Our results show that MICP occurs due to two distinct interactions: Firstly, mechanical stress on vegetative cells can cause leakage and/or lysis, releasing sequestered bicarbonate into the environment, resulting in the formation of new crystals. Secondly, close contact between a heterocyst and a calcite crystal seed appears to cause rapid crystal growth. To our knowledge, the latter interaction has not been reported previously. By providing greater insight into MICP caused by Anabaena, these results increase our understanding of the interplay between cyanobacteria and calcium carbonate precipitation, which plays a role in oceanic buffering and mineral formation around the globe.

Unravelling the acclimation strategies in thermophilic cyanobacterium Mastigocladus sp. TA-8 at sub-optimal temperature using proteomics coupled with physiological and biochemical attributes.

This study employed the paper disc diffusion method to evaluate the antibacterial efficacy and toxicity profile of culture filtrate and C-phycocyanin extracted from the filamentous freshwater cyanobacterium Westiellopsis sp. against three pathogenic bacteria: Bacillus subtilis (Gram-positive), Pseudomonas sp. (Gram-negative), and Xanthomonas sp. (Gram-negative), resulting in inhibition zones ranging from 1.3 ± 0.2 mm to 13.2 ± 0.5 mm. Toxicity was assessed using a silkworm (Bombyx mori) bioassay. Larvae fed with C-phycocyanin extracts from different strains showed increased total body weight (65.1-102.6% increase) and silk gland weight (209.1-240.9% increase) compared to controls, with no observed adverse effects. Statistical analysis confirmed these increases were highly significant (p < 0.001). These results demonstrate that both the crude culture filtrate and the refined pigment possess notable antibacterial properties and exhibit a favorable safety profile in an invertebrate model. The dual activity of these natural extracts supports their potential application as alternative antibacterial agents in agricultural and medicinal contexts. Future studies should focus on comprehensive molecular characterization of active compounds, determination of minimum inhibitory concentrations (MIC), and expanded toxicity testing in mammalian models to confirm clinical viability.

Protocol to investigate gene expression heterogeneity in cyanobacteria using mRNA CARD-FISH

RecF-RecO-RecR proteins of the cyanobacterium Nostoc PCC 7120: Novel insights into their interactions and role in high radioresistance.

>Abstract Lake Manych-Gudilo is a relict lake formed 2–3 million years ago at the site of the ancient strait connecting the Black and Caspian seas. During the dry season, total water salinity exceeds 50 g/L, with the levels of sulfate and magnesium in the brine higher than in the ocean water. The coastline has numerous bays and separating shallow basins. The article reports the results of investigation of microbial biodiversity in the algo-bacterial mat in a shallow basin with salinity varying from 40 to 70 g/L, which is associated with Lake Manych-Gudilo. The studied mat had the properties of a sulfuret, a community with an intense sulfur turnover. Microalgae of the genus Cladophora and filamentous cyanobacteria were the main producers of organic matter in the benthic community. Among the anoxygenic phototrophic bacteria isolated in pure cultures, halophilic purple sulfur bacteria Ectothiorhodospira marina and Lamprobacter modestohalophilus and green sulfur bacteria Prosthecochloris sp. predominated. Nonsulfur purple bacteria Rhodovulum adriatica , also present in the community, were able to use sulfide for photosynthesis. All identified species were typical of microbial mats of saline and hypersaline basins with elevated levels of sulfate and bivalent cations. The algo-bacterial mat was reconstructed in the laboratory at 80 g/L salinity using a Winogradsky column. Microbial diversity of the experimental mat was studied by sequencing the 16S rRNA gene fragments. The data obtained improved our understanding of bacterial species diversity in microbial mats adapted to extreme hypersaline conditions.

The human population are continuously increasing; the concern about food, global warming, outbreak of diseases, and other environmental issues are also increased but thanks to nature which provides a viable solution and a good resource which are cyanobacteria (blue-green algae). Spirulina platensis is spiral coil blue-green algae, free- floating filamentous undifferentiated cyanobacterium that live both in the sea and freshwater and belong to the family of Oscillatoriaceae. They are non-heterocyst found in warm bodies of water in tropical and subtropical regions with high elevated pH, salinity, carbonate & bicarbonate content. Spirulina has different pigments such as carotenes, phycobilins, chlorophylls, phycocyanin and phycoerythrin. It contains high protein, chemicals, vitamins and various bioactive compounds used as food supplements, therapeutics, and diagnostics. Spirulina has antioxidant, antimicrobial, antibacterial, anti-inflammatory, and antiparasitic properties which play an important role in human life. Spirulina is used as a model organism in a variety of studies in medical sciences, environmental science, and biotechnology. The aim of this review is to summarize the importance of cyanobacterial species on human health.

Phototaxis refers to an organism's movement toward a light source, while photophobotaxis involves movement into illuminated regions. Although phototaxis in cyanobacteria has been widely studied, photophobotaxis has been investigated in only a few species. In this study, we examined photophobotaxis of 7 single-celled and 11 filamentous cyanobacterial species, among them 3 Nostocales (filaments with heterocysts) and 5 Oscillatoriales and 1 Desertifiliales member. All single-celled species and all Oscillatoriales/Desertifiliales exhibited photophobotaxis, whereas no evidence of photophobotaxis was found for the Nostocales and two other species. A pilus-free mutant of Synechocystis sp. PCC 6803 did not display this behavior. The photosystem II inhibitor DCMU disrupted photophobotaxis in single-celled and filamentous cyanobacteria at a concentration of 10 μM; only the filamentous Phormidium lacuna (P. lacuna) required 100 μM DCMU for inhibition. This points to PS II as a sensor of photophobotaxis. The widespread occurrence of photophobotaxis aligns with the universality of photosystems. Previous studies on spectral sensitivity and the cyanobacteriochrome PixJ in P. lacuna identified PixJ as a negative regulator of photophobotaxis. In pixJ mutants, light sensitivity was increased compared with the wild-type. Dual-wavelength experiments confirmed that yellow light induces PixJ to downregulate photophobotaxis. Our experiments also show that P. lacuna moves faster in darkness than in light and that a temporal change of light intensity from light to dark can induce a change of movement direction. Both findings support the light trap model which is based on random movement and a change of movement direction at the light-dark border.

Cyanobacterial blooms have become a worldwide problem. Chemical algicides play important role in controlling cyanobacterial blooms in spite of their potential secondary pollution to aquatic environments. The algicidal microorganisms and their metabolites are potential substitutes for non-selective chemical algicides because of their environmentally friendly characteristics. In this paper, an actinomycete strain, designated as LMJ-114, capable of eliminating cyanobacteria, was isolated from a soil sample collected from Lushan Mountains of China. Strain LMJ-114, belonging to Streptomyces, showed the highest similarity to Streptomyces jiujiangensis JXJ 0074T based on the 16S rRNA gene sequences. This strain showed algicidal activities on both Microcystis and filamentous cyanobacteria. The extracellular water-soluble substances exhibited strong algicidal activity on Microcystis aeruginosa FACHB-905. The algicidal components from strain LMJ-114 could induce M. aeruginosa to produce massive reactive oxygen species (ROS), and seriously affected its antioxidant system. Lipid peroxidation, therefore, occurred seriously in cells of M. aeruginosa, which resulted in 91.6–525.2% higher of malondialdehyde (MDA), and disintegration of gelatinous sheaths, and subsequent sunk cell surface and perforation of the cells. The treatments of both culture broth supernatant and mycelia of strain LMJ-114 significantly affected the contents of retinoic acids (RAs) and microcystins (MCs), and 4 days later, RAs eliminated completely, and 7 days later, microcystin RR (MC-RR) decreased by 96.7 and 87.9%, respectively, and microcystin LR (MC-LR) contents decreased by 89.9 and 81.0%, respectively. L-valine was one of the algicidal compounds in the culture broth supernatant of strain LMJ-114. Strain LMJ-114 and its extracellular metabolites showed potential application in controlling cyanobacterial blooms.

ABSTRACT Cyanobacterial mass productions are in the focus of extensive research due to their increasing extent and frequency in recent decades. It is hypothesized that the continuous release of cyanobacterial cell content due to cell lysis during and at the end of a bloom could result in environmental stress and induce resting stage formation in algae capable of altering their life cycle in this manner. However, our knowledge of the subject is incomplete. Therefore in the present study, cultures of the green alga Haematococcus lacustris were treated with the cell lysate of cylindrospermopsin producing filamentous cyanobacterium Umezakia ovalisporum. The changes of cell types in the treated cultures suggest that cylindrospermopsin containing cyanobacterial lysate induced cyst formation but inhibited the maturation of these resting cells. Concurrent with alterations in cell type, there was an increase in phosphatase activities in cultures treated with cyanobacterial lysate, consistent with earlier observations involving other eukaryotic algae and cyanobacteria. Astaxanthin accumulation was reduced in cyanobacterial lysate treated cultures, and this phenomenon was accompanied by a concomitant reduction in lipid accumulation. The amounts of most of the identified fatty acids exhibited negative correlations with the increasing cyanobacterial lysate content in the treatments. These findings suggest that cyanobacterial cell content in the environment exerts a deleterious effect on carotenoid and lipid synthesis, i.e. on the maturation of cysts. These results elucidate the potential adverse consequences of cyanobacterial cell content on resting stage formation and underscore the community forming significance of cyanobacterial cell contents.

Plastisphere dynamics in Mediterranean aquaculture: Microbial colonization and pollution in fish farm cages.

Actin proteins are common to all domains of life and exhibit ATP-dependent polymerization to form filaments. In bacteria, four families of bacterial actin-like proteins (BALPs) have been identified and characterized. These BALPs are involved in plasmid partitioning (ParM), cell division (FtsA), magnetosome positioning (MamK), and cell morphology (MreB). Here, we report the identification of a fifth family of BALP, FcmB. Using the model filamentous cyanobacterium Nostoc punctiforme, we demonstrate that FcmB is a BALP that regulates cell morphology in filamentous cyanobacteria. Deletion of fcmB, or fcmC, which encodes an FcmB-interacting protein, resulted in the loss of rod morphology, similar to the phenotype reported for mreB mutants in other bacteria, including cyanobacteria. However, despite the apparent functional similarity, fcmB is not a paralog of mreB, but rather was acquired by horizontal gene transfer of a plasmid partitioning system and subsequent integration into the chromosome. Fluorescent protein fusions and immunofluorescence demonstrate that FcmB forms membrane-bound filaments which wrap around the circumference of the cell, while FcmC is localized to discrete membrane-associated foci and is essential for proper membrane localization of FcmB. Protein-protein interactions were detected between FcmB and FcmC, but not MreB, indicating that FcmB and MreB do not form heterofilaments. It is currently unclear how FcmBC exerts its effect on cell morphology, but both mreB and fcmB are ubiquitous in the developmentally complex heterocyst-forming filamentous cyanobacteria, and the presence of two discrete systems modulating cell morphology may be critical for the remarkable degree of phenotypic plasticity observed in these organisms.IMPORTANCEFilament-forming actin proteins are found in nearly all living organisms. In bacteria, four families of actin proteins have been defined, with biological functions in plasmid partitioning, cell division, magnetosome positioning, and cell morphology. Here, we identify and characterize FcmB, a fifth family of bacterial actin proteins found in filamentous cyanobacteria, and demonstrate that this family evolved from plasmid partitioning actins but influences cell morphology rather than DNA segregation. Filamentous cyanobacteria exhibit substantial phenotypic plasticity and typically contain both FcmB and MreB, the other actin family known to regulate cell morphology. The presence of two distinct families of actin proteins influencing cell morphology may play a critical role in the ability of these organisms to rapidly alter their cell shape.

Ribonuclease E (RNase E) is central to bacterial RNA metabolism. In cyanobacteria, its activity is inhibited by RebA, a key mechanism for controlling cell morphology. Here, we demonstrate that rebA is essential for diazotrophic growth of Anabaena PCC 7120, a filamentous cyanobacterium capable of forming heterocysts—specialized nitrogen‐fixing cells—upon nitrogen starvation. The rebA mutant strain (ΔrebA) showed severe growth defects in nitrogen‐deprived conditions, despite forming more heterocysts than the wild type. With a GFP fusion strain, we show that RebA is transiently upregulated during heterocyst differentiation. Microscopic and ultrastructural analyses revealed that ΔrebA heterocysts accumulated abnormally large cyanophycin granules, while vegetative cells showed reduced pigment levels and disorganized thylakoid membranes, phenotypes indicative of a severe nitrogen deficiency response. However, esculin tracer diffusion and SepJ‐GFP localization in ΔrebA were comparable to the wild type, suggesting that cell–cell communication via septal junctions remains functional. Thus, the growth defect likely results from impaired degradation or mobilization of fixed nitrogen. Notably, the ΔrebA phenotype could be rescued only by wild‐type RebA, but not by variants unable to bind RNase E, indicating that RebA's function depends on its modulation of RNase E activity. Together, these findings reveal a key posttranscriptional mechanism linking RNase E regulation to heterocyst development and intercellular nutrient transfer, highlighting the importance of regulated RNA metabolism for diazotrophic growth.

Abstract Interactions between organisms of different trophic levels are not only involved in the functioning of aquatic systems such as rivers but also crucial to maintaining taxonomic and functional diversity. This study aimed to evaluate the diversity of benthic cyanobacteria and their role as facilitating species for the colonization of benthic macroinvertebrates (MIB) in tropical mountain rivers with varying ecological conservation statuses. We sampled ten river segments in central Mexico, assessing physical and chemical parameters and collecting macroscopic cyanobacterial growths. A taxonomic and morphofunctional characterization was conducted for both biological groups, while a land-use change index (CDI) was calculated to assess the ecological quality of the sites. The analysis of similarities (ANOSIM) showed that cyanobacterial taxa are the factor that determines significant differences in the composition of MIB assemblages, with Cricotopus, Tanytarsini, Simulium, and Baetis being the most representative taxa according to the similarity percentage analysis (SIMPER). We also constructed an interactions network comprising eight cyanobacterial and 32 MIB taxa. The dominance of dipterans reflects substrate specialization, while the prevalence of collector morphologies suggests indirect food acquisition. While MIB were observed in unilateral associations with filamentous cyanobacteria, they formed multilateral associations with colonial species. Cricotopus showed a preference for both Nostoc tlalocii and Cyanoplacoma aff. regulare, revealing nonexclusive mutualistic relationships. This study demonstrated that cyanobacteria are important substrates for MIB to complete their life cycle, including the use of different species that are similar in their level of organization and therefore thallus morphology. This interaction network demonstrates adaptability, with some interactions being nonexclusive. Substrate turnover and voltinism in MIB may be linked to resiliency in the face of habitat changes caused by anthropogenic activities in the studied river basins.

Siderophores are low-molecular-weight compounds excreted by microorganisms to acquire iron and possibly to monopolize iron resource to achieve competitive advantage over other strains, or to trade for other substrates in mutualistic relationships. Siderophores that employ β-hydroxy-aspartate (β-OH-Asp) for iron chelation can undergo UV-mediated photolytic cleavage, simultaneously reducing Fe3+ to Fe2+. Photolytic siderophores can promote algal-bacterial mutualism, where the bacteria provide iron in exchange for dissolved organic carbon. We present a comprehensive characterization of cyanochelin B, a photolytic β-OH-Asp-containing siderophore produced by the filamentous cyanobacterium Leptolyngbya sp. NIES-3755. Combining nuclear magnetic resonance, high-resolution mass spectrometry, bioinformatic analyses, and Marfey's and Murata's method, we elucidated the structure of cyanochelin B, including the configuration of its stereocenters. Cyanochelin B-iron complexes rapidly photolyse under UV light (t1/2 = 2.3 min; 19.6 µmol m-2 s-1 UV-A) and release Fe2+. Using a coculture setup with Leptolyngbya and Synechocystis sp. PCC 6803 (a non-siderophore producer) in membrane-separated compartments and alginate-embedded FeCl3 to simulate poorly accessible precipitated iron, we demonstrate cyanochelin B mode of actions. Our results show that in the absence of UV light, cyanochelin B efficiently monopolizes iron, favoring Leptolyngbya. However, UV light eliminates this monopolization, making iron available to any cohabiting, also possibly competing, organisms. We further report isolating novel cyanochelin B-producing Phormidesmis strains from field material and discuss the broader implications of photolytic siderophores. In conclusion, our interdisciplinary approach led to the discovery of a novel photolytic siderophore, cyanochelin B, and highlighted its possible role in distributing iron in microbial communities.IMPORTANCEIron is an essential micronutrient that is required by all living organisms as a cofactor of indispensable enzymes. Due to its specific properties, it is mostly precipitated and is biologically unavailable. Microbes produce siderophores, low-molecular-weight compounds that bind iron, to facilitate iron uptake. Siderophores are mediators of microbial interactions and facilitate competitive exclusion of non-compatible strains or support mutualistic partners and cheater strains. Here, we adopt an interdisciplinary strategy and report a complete structural elucidation of cyanochelin B, a photolytic cyanobacterial siderophore that contains β-hydroxy-aspartate (β-OH-Asp). Our coculture experiments show that cyanochelin B can either monopolize iron to its producer or make it accessible to other strains, depending on the presence of UV light. Moreover, our data suggest that the benefits from production of photolytic siderophores are not restricted to the producer or cohabiting bacteria but are rather available to the entire irradiated community. Out of the known siderophores, 17.5% contain the photoreactive β-OH-Asp and therefore may play a similar role.

Chytrids infect and kill various phytoplankton. Studies of chytrids infecting cyanobacteria and microalgae have focused only on a few host–parasite systems (hosts mainly Planktothrix and Asterionella). Here we focus on a newly isolated and recently described chytrid that infects the nitrogen-fixing filamentous cyanobacterium Dolichospermum. This species specializes in infecting heterocyst cells only and may therefore affect the nitrogen fixation process. We performed infection experiments where Dolichospermum was exposed to the chytrid under nitrogen-limited and nitrogen-replete conditions and quantified the effects of infection on host nitrogen fixation and growth. Chytrid infection strongly decreased host growth under nitrogen-limited conditions, but not under nitrogen-rich. This was because the cyanobacterium could only obtain nitrogen from its partially infected heterocysts, which, despite the parasitism, retained some capacity for nitrogen fixation under nitrogen-limited conditions, but at a reduced level. Host filaments partially compensated for chytrid infection by increasing nitrogen fixation rates nearly 8-fold in the remaining heterocysts that survived infection. Nitrogen fixation rates were reduced by ⁓50% in infected Dolichospermum when normalized to biovolume, compared to uninfected controls. This reduction in the supply of nitrogen through nitrogen fixation and cyanobacterial development suggests that chytrid parasites may shape cyanobacterial bloom development and nitrogen fixation in nature.

The Hik2-Rre1 interaction acts as a two-component signaling system in filamentous cyanobacterium Anabaena PCC 7120.

A pair of new strains was obtained from a natural environment and identified as the filamentous non-heterocystous cyanobacterium SZ2 and the rhizobia Ensifer/Sinorhizobium sp. ST1. This pair was of particular interest because it could potentially perform both photosynthesis and nitrogen fixation. Interactions and material production were investigated in a new co-culture system using the "natural pair" of these strains. Cocultivation was favorable under both mixotrophic (coMC) and autotrophic conditions (coAC) when material production was assessed using heptadecane (C17H36) from the SZ2 strains. Under coAC, where nitrogen is depleted, some soluble factor(s) produced by the co-culture-possibly including ammonium ions-appear to function as biomass-increasing factors (BIFs), contributing to the enhanced accumulation of chlorophyll a in SZ2, along with extracellular polysaccharides, lipids, carbohydrates, and proteins in the total biomass. A notable feature of this "aquatic" coAC system is that it overcomes biomass reduction under nitrogen-deficient conditions, which is difficult in monoculture systems and can contribute to economic material production for biorefineries.