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BackgroundThe cyanobacterial genus Nostoc includes several species forming centimetre-large gelatinous colonies in nutrient-poor freshwaters and harsh semi-terrestrial environments with extended drought or freezing. These Nostoc species have filaments with normal photosynthetic cells and N2-fixing heterocysts embedded in an extensive gelatinous matrix of polysaccharides and many other organic substances providing biological and environmental protection. Large colony size imposes constraints on the use of external resources and the gelatinous matrix represents extra costs and reduced growth rates.ScopeThe objective of this review is to evaluate the mechanisms behind the low rates of growth and mortality, protection against environmental hazards and the persistence and longevity of gelatinous Nostoc colonies, and their ability to economize with highly limiting resources.ConclusionsSimple models predict the decline in uptake of dissolved inorganic carbon (DIC) and a decline in the growth rate of spherical freshwater colonies of N. pruniforme and N. zetterstedtii and sheet-like colonies of N. commune in response to a thicker diffusion boundary layer, lower external DIC concentration and higher organic carbon mass per surface area (CMA) of the colony. Measured growth rates of N. commune and N. pruniforme at high DIC availability comply with general empirical predictions of maximum growth rate (i.e. doubling time 10–14 d) as functions of CMA for marine macroalgae and as functions of tissue thickness for aquatic and terrestrial plants, while extremely low growth rates of N. zetterstedtii (i.e. doubling time 2–3 years) are 10-fold lower than model predictions, either because of very low ambient DIC and/or an extremely costly colony matrix. DIC uptake is limited by diffusion at low concentrations for all species, although they exhibit efficient HCO3– uptake, accumulation of respiratory DIC within the colonies and very low CO2 compensation points. Long light paths and light attenuation by structural substances in large Nostoc colonies cause lower quantum efficiency and assimilation number and higher light compensation points than in unicells and other aquatic macrophytes. Extremely low growth and mortality rates of N. zetterstedtii reflect stress-selected adaptation to nutrient- and DIC-poor temperate lakes, while N. pruniforme exhibits a mixed ruderal- and stress-selected strategy with slow growth and year-long survival prevailing in sub-Arctic lakes and faster growth and shorter longevity in temperate lakes. Nostoc commune and its close relative N. flagelliforme have a mixed stress–disturbance strategy not found among higher plants, with stress selection to limiting water and nutrients and disturbance selection in quiescent dry or frozen stages. Despite profound ecological differences between species, active growth of temperate specimens is mostly restricted to the same temperature range (0–35 °C; maximum at 25 °C). Future studies should aim to unravel the processes behind the extreme persistence and low metabolism of Nostoc species under ambient resource supply on sediment and soil surfaces.

Nostoc cyanobacteria are among the few organisms capable of fixing both carbon and nitrogen. These metabolic features are essential for the cyanolichen symbiosis, where Nostoc supplies both carbon (as glucose) and nitrogen (as ammonium) to a cyanolichen-forming fungal partner. This nutrient flow was established by seminal biochemical studies published in the 20th century. Since then, cyanolichen metabolism has received little attention, and the molecular mechanisms that underlie the physiology of lichenized Nostoc remain mostly unknown. Here, we aimed to elucidate the genomic and transcriptional changes that enable Nostoc’s metabolic role in cyanolichens. We used comparative genomics across 243 genomes of Nostoc s. lat. coupled with metatranscriptomic experiments using Peltigera cyanolichens. We found that genes for photoautotrophic carbon fixation are upregulated in lichenized Nostoc. This likely results in a higher rate of carbon fixation that allows Nostoc to provide carbon to the fungal partner while meeting its own metabolic needs. We also found that the transfer of ammonium from Nostoc to the lichen-forming fungus is facilitated by two molecular mechanisms: (i) transcriptional downregulation of glutamine synthetase, the key enzyme responsible for ammonium assimilation in Nostoc; and (ii) frequent losses of a putative high-affinity ammonium permease, which likely reduces Nostoc’s capacity to recapture leaked ammonium. Finally, we found that the development of motile hormogonia is downregulated in lichenized Nostoc, which resembles the repression of motility in Nostoc symbionts after they colonize symbiotic cavities of their plant hosts. Our results pave the way for a revival of cyanolichen ecophysiology in the omics era.

Most organisms performing oxygenic photosynthesis contain either cytochrome c sub(6) or plastocyanin, or both, to transfer electrons from cytochrome b sub(6)-f to photosystem I. Even though plastocyanin has superseded cytochrome c sub(6) along evolution, plants contain a modified cytochrome c sub(6), the so called cytochrome c sub(6A), whose function still remains unknown. In this article, we describe a second cytochrome c sub(6) (the so called cytochrome c sub(6)-like protein), which is found in some cyanobacteria but is phylogenetically more related to plant cytochrome c sub(6A) than to cyanobacterial cytochrome c sub(6). In this article, we conclude that the cytochrome c sub(6)-like protein is a putative electron donor to photosystem I, but does play a role different to that of cytochrome c sub(6) and plastocyanin as it cannot accept electrons from cytochrome f. The existence of this third electron donor to PSI could explain why some cyanobacteria are able to grow photoautotrophically in the absence of both cytochrome c sub(6) and plastocyanin. In any way, the Cyt c sub(6)-like protein from Nostoc sp. PCC 7119 would be potentially utilized for the biohydrogen production, using cell-free photosystem I catalytic nanoparticles.

The microplastics polymer—polystyrene, polyethylene, polyvinyl chloride, etc. are now recognized as potent threats to the aquatic system due to the Trojan horse effect i.e., they adsorb other pollutants such as pharmaceutical drugs, organic solvents, metals etc. and act as a vector or carrier. Polystyrene (PS) is one of the most usable plastics worldwide that abundantly contaminates the aquatic body. However, to date, only a few studies have focused on the eco-toxic effects of polystyrene in combination with other pollutants. Therefore, in the present study, the effect of polystyrene (pristine) and spiked with the emerging pollutant paracetamol (PCM) was studied on cyanobacterium- Nostoc muscorum. PS, spiked with paracetamol exhibited a higher adverse effect on the growth and biochemical constituents. Fluorescence intensities of confocal images of the samples decreased with increasing toxic effect of polystyrene when spiked with paracetamol. Increased laccase and esterase activity also indicated the degradation potential of Nostoc muscorum. The findings of present work suggested PS (Pristine and spiked with PCM) toxicity on primary producer of ecosystem and role of cyanobacterial degrading enzymes in bioremediation of PS. Therefore, it is better to “nip in the bud” the plastic pollution rather than to face a great environmental threat.

Cyanobacteria are photosynthetic prokaryotes found in a range of environments. They are infamous for the production of toxins, as well as bioactive compounds, which exhibit anticancer, antimicrobial and protease inhibition activities. Cyanobacteria produce a broad range of antifungals belonging to structural classes, such as peptides, polyketides and alkaloids. Here, we tested cyanobacteria from a wide variety of environments for antifungal activity. The potent antifungal macrolide scytophycin was detected in Anabaena sp. HAN21/1, Anabaena cf. cylindrica PH133, Nostoc sp. HAN11/1 and Scytonema sp. HAN3/2. To our knowledge, this is the first description of Anabaena strains that produce scytophycins. We detected antifungal glycolipopeptide hassallidin production in Anabaena spp. BIR JV1 and HAN7/1 and in Nostoc spp. 6sf Calc and CENA 219. These strains were isolated from brackish and freshwater samples collected in Brazil, the Czech Republic and Finland. In addition, three cyanobacterial strains, Fischerella sp. CENA 298, Scytonema hofmanni PCC 7110 and Nostoc sp. N107.3, produced unidentified antifungal compounds that warrant further characterization. Interestingly, all of the strains shown to produce antifungal compounds in this study belong to Nostocales or Stigonematales cyanobacterial orders.

Abstract Three epilithic cyanobacterial strains were isolated from the scrapings of a single rock surface from the Reshi River in Sikkim, India. At the time of sampling, the rock surface did not show any visible cyanobacterial growth; however, the surface of the rock was glistering. Subsequent morphological analysis indicated that two out of three strains exhibited typical Nostoc-like morphology and the third strain had cell division in multiple planes showing typical morphology of a member of the family Hapalosiphonaceae. Further, 16S rRNA gene phylogeny indicated the strains to be members of the genera Nostoc, Desmonostoc, and Westiellopsis. For species-level demarcation, additionally, 16S–23S ITS (Internal Transcribed Spacer) region analysis was performed, which indicated that the strain RESHI-1B-PS was a novel cyanobacterial lineage of the genus Nostoc, while the strains RESHI-1A-PS and RESHI-1C-PS were representatives of Desmonostoc sp. and Westiellopsis prolifica, respectively. Thus, in the current investigation, we have described an undocumented species of the cyanobacteria, which we named Nostoc sikkimense in accordance with the guidelines outlined in the International Code of Nomenclature for algae, fungi, and plants (ICN). The study also enumerates and illustrates different life cycle stages of N. sikkimense RESHI-1B-PS along with further expanding the geographic distribution of W. prolifica and its substantial ecological adaptability. We describe a new species of epilithic cyanobacteria from northeastern India.

Based on our previous findings that salicylic acid and jasmonic acid increased Nostoc flagelliforme polysaccharide yield by regulating intracellular nitric oxide (NO) levels, the mechanism through which NO affects polysaccharide biosynthesis in Nostoc flagelliforme was explored from the perspective of S-nitrosylation (SNO). The addition of NO donor and scavenger showed that intracellular NO had a significant positive effect on the polysaccharide yield of N. flagelliforme . To explore the mechanism, we investigated the relationship between NO levels and the activity of several key enzymes involved in polysaccharide biosynthesis, including fructose 1,6-bisphosphate aldolase (FBA), glucokinase (GK), glucose 6-phosphate dehydrogenase (G6PDH), mitochondrial isocitrate dehydrogenase (ICDH), and UDP-glucose dehydrogenase (UGDH). The enzymatic activities of G6PDH, ICDH, and UGDH were shown to be significantly correlated with the shifts in intracellular NO levels. For further validation, G6PDH, ICDH, and UGDH were heterologously expressed in Escherichia coli and purified via Ni + -NAT affinity chromatography, and subjected to a biotin switch assay and western blot analysis, which revealed that UGDH and G6PDH were susceptible to SNO. Furthermore, mass spectrometry analysis of proteins treated with S-nitrosoglutathione (GSNO) identified the SNO modification sites for UGDH and G6PDH as cysteine 423 and cysteine 249, respectively. These findings suggest that NO modulates polysaccharide biosynthesis in N. flagelliforme through SNO of UGDH and G6PDH. This reveals a potential mechanism through which NO promotes polysaccharide synthesis in N. flagelliforme , while also providing a new strategy for improving the industrial production of polysaccharides.

OBJECTIVES: To assess the effects of light intensity and quality on the growth and phycobiliproteins (PBP) accumulation in Nostoc sphaeroides Kützing (N. sphaeroides). RESULTS: Dry weights, dry matter, protein, chlorophyll and PBP contents were higher under 90 μmol m⁻² s⁻¹ than under other intensities (both higher and lower). Phycocyanin and allophycocyanin increased with light intensity while phycoerythrin decreased. Fresh weights, protein and PBP contents increased at the highest rates under blue light. Red light resulted in higher values of dry matter, phycocyanin and chlorophyll a. CONCLUSION: White light at 90 μmol m⁻² s⁻¹ or blue light 30 μmol m⁻² s⁻¹ were optimal for the growth and phycobiliprotein accumulation in N. sphaeroides.

During the past decades, the importance of developing sustainable, carbon dioxide (CO 2 )-neutral and biodegradable alternatives to conventional plastic has become evident in the context of global pollution issues. Therefore, heterotrophic bacteria such as Cupriavidus sp. have been intensively explored for the synthesis of the biodegradable polymer polyhydroxybutyrate (PHB). PHB is also naturally produced by a variety of phototrophic cyanobacteria, which only need sunlight and CO 2, thereby allowing a CO 2 negative, eco-friendly synthesis of this polymer. However, a major drawback of the use of cyanobacteria is the need of a two-stage production process, since relevant amount of PHB synthesis only occurs after transferring the cultures to conditions of nitrogen starvation, which hinders continuous, large-scale production. This study aimed at generating, by means of genetic engineering, a cyanobacterium that continuously produces PHB in large amounts. We choose a genetically amenable filamentous cyanobacterium of the genus Nostoc sp., which is a diazotrophic cyanobacterium, capable of atmospheric nitrogen (N 2 ) fixation but naturally does not produce PHB. We transformed this Nostoc strain with various constructs containing the constitutive promotor P psbA and the PHB synthesis operon phaC1AB from Cupriavidus necator H16. In fact, while the transformants initially produced PHB, the PHB-producing strains rapidly lost cell viability. Therefore, we next attempted further optimization of the biosynthetic gene cluster. The PHB operon was expanded with phasin gene phaP1 from Cupriavidus necator H16 in combination with the native intergenic region of apcBA from Nostoc sp. 7120. Finally, we succeeded in stabilized PHB production, whilst simultaneously avoiding decreasing cell viability. In conclusion, the recombinant Nostoc strain constructed in the present work constitutes the first example of a continuous and stable PHB production platform in cyanobacteria, which has been decoupled from nitrogen starvation and, hence, harbours great potential for sustainable, industrial PHB production.

Inclusions of neutral lipids termed lipid droplets (LDs) located throughout the cell were identified in the cyanobacterium Nostoc punctiforme by staining with lipophylic fluorescent dyes. LDs increased in number upon entry into stationary phase and addition of exogenous fructose indicating a role for carbon storage, whereas high-light stress did not increase LD numbers. LD accumulation increased when nitrate was used as the nitrogen source during exponential growth as compared to added ammonia or nitrogen-fixing conditions. Analysis of isolated LDs revealed enrichment of triacylglycerol (TAG), α-tocopherol, and C17 alkanes. LD TAG from exponential phase growth contained mainly saturated C16 and C18 fatty acids, whereas stationary phase LD TAG had additional unsaturated fatty acids characteristic of whole cells. This is the first characterization of cyanobacterial LD composition and conditions leading to their production. Based upon their abnormally large size and atypical location, these structures represent a novel sub-organelle in cyanobacteria.