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Increasing antibiotic resistance and the emergence of multidrug-resistant (MDR) pathogens have led to the need to develop new therapeutic agents to tackle microbial infections. Nano-antibiotics are a novel generation of nanomaterials with significant antimicrobial activities that target bacterial defense systems including biofilm formation, membrane permeability, and virulence activity. In addition to AgNO the current study aimed to explore for first time the antibacterial potential of silver nanoparticles synthesized by sp. Bahar_M (N-SNPs) and their killing mechanisms against , methicillin-resistant , and . Potential mechanisms of action of both silver species against bacteria were systematically explored using agar well diffusion, enzyme (lactate dehydrogenase (LDH) and ATPase) and antioxidant (glutathione peroxidase and catalase)   assays, and morphological examinations. qRT-PCR and SDS-PAGE were employed to investigate the effect of both treatments on , and gene expression and protein patterns, respectively. N-SNPs exhibited greater biocidal activity than AgNO against the four tested bacteria. treated with N-SNPs showed significant surges in LDH levels, imbalances in other antioxidant and enzyme activities, and marked morphological changes, including cell membrane disruption and cytoplasmic dissolution. N-SNPs caused more significant upregulation of expression and downregulation of both and expression and increased protein denaturation compared with AgNO . N-SNPs exhibited significant inhibitory potential against by direct interfering with bacterial cellular structures and/or enhancing oxidative stress, indicating their potential for use as an alternative antimicrobial agent. However, the potential of N-SNPs to be usable and biocompatible antibacterial drug will evaluate by their toxicity against normal cells.

Cyanobacteria produce a range of secondary metabolites, one being the neurotoxic non-protein amino acid β-N-methylamino-L-alanine (BMAA), proposed to be a causative agent of human neurodegeneration. As for most cyanotoxins, the function of BMAA in cyanobacteria is unknown. Here, we examined the effects of BMAA on the physiology of the filamentous nitrogen-fixing cyanobacterium Nostoc sp. PCC 7120. Our data show that exogenously applied BMAA rapidly inhibits nitrogenase activity (acetylene reduction assay), even at micromolar concentrations, and that the inhibition was considerably more severe than that induced by combined nitrogen sources and most other amino acids. BMAA also caused growth arrest and massive cellular glycogen accumulation, as observed by electron microscopy. With nitrogen fixation being a process highly sensitive to oxygen species we propose that the BMAA effects found here may be related to the production of reactive oxygen species, as reported for other organisms.

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.

Cadmium (Cd) and lead (Pb) are global environmental pollutants. In this study, Nostoc sp. MK-11 was used as an environmentally safe, economical, and efficient biosorbent for the removal of Cd and Pb ions from synthetic aqueous solutions. Nostoc sp. MK-11 was identified on a morphological and molecular basis using light microscopic, 16S rRNA sequences and phylogenetic analysis. Batch experiments were performed to determine the most significant factors for the removal of Cd and Pb ions from the synthetic aqueous solutions using dry Nostoc sp. MK1 biomass. The results indicated that the maximum biosorption of Pb and Cd ions was found under the conditions of 1 g of dry Nostoc sp. MK-11 biomass, 100 mg/L of initial metal concentrations, and 60 min contact time at pH 4 and 5 for Pb and Cd, respectively. Dry Nostoc sp. MK-11 biomass samples before and after biosorption were characterized using FTIR and SEM. A kinetic study showed that a pseudo second order kinetic model was well fitted rather than the pseudo first order. Three isotherm models Freundlich, Langmuir, and Temkin were used to explain the biosorption isotherms of metal ions by Nostoc sp. MK-11 dry biomass. Langmuir isotherm, which explains the existence of monolayer adsorption, fitted well to the biosorption process. Considering the Langmuir isotherm model, the maximum biosorption capacity (qmax) of Nostoc sp. MK-11 dry biomass was calculated as 75.757 and 83.963 mg g−1 for Cd and Pb, respectively, which showed agreement with the obtained experimental values. Desorption investigations were carried out to evaluate the reusability of the biomass and the recovery of the metal ions. It was found that the desorption of Cd and Pb was above 90%. The dry biomass of Nostoc sp. MK-11 was proven to be efficient and cost-effective for removing Cd and especially Pb metal ions from the aqueous solutions, and the process is eco-friendly, feasible, and reliable.

Green nanoparticles represent a revolution in bionanotechnology, providing opportunities to fight life-threatening diseases, such as cancer, with less risk to the environment and to human health. Here, for the first time, we systematically investigated the anticancer activity and possible mechanism of novel silver nanoparticles (N-SNPs) synthesized by Nostoc Bahar M against the MCF-7 breast cancer cells, HCT-116 colorectal adenocarcinoma cells, and HepG2 liver cancer cells, using cell viability assays, morphological characterization with inverted light and transmission electron microscopy, antioxidants and enzymes (glutathione peroxidase (GPx), glutathione (GSH), adenosine triphosphatase (ATPase), and lactate dehydrogenase (LDH)), and western blotting (protein kinase B (Akt), phosphorylated-Akt (p-Akt), mammalian target of rapamycin (mTOR), B-cell lymphoma 2 (Bcl-2), tumor suppressor (p53), and caspase 3). N-SNPs decreased the viability of MCF-7, HCT-116, and HepG2 cells, with half-maximal inhibitory concentrations of 54, 56, and 80 µg/mL, respectively. They also significantly increased LDH leakage, enhanced oxidative stress via effects on antioxidative markers, and caused metabolic stress by significantly decreasing ATPase levels. N-SNPs caused extensive ultrastructural alterations in cell and nuclear structures, as well as in various organelles. Furthermore, N-SNPs triggered apoptosis via the activation of caspase 3 and p53, and suppressed the mTOR signaling pathway via downregulating apoptosis-evading proteins in MCF-7, HCT-116, and HepG2 cells. Ultrastructural analysis, together with biochemical and molecular analyses, revealed that N-SNPs enhanced apoptosis via the induction of oxidative stress and/or through direct interactions with cellular structures in all tested cells. The cytotoxicity of Nostoc-mediated SNPs represents a new strategy for cancer treatment via targeting various cell death pathways. However, the potential of N-SNPs to be usable and biocompatible anticancer drug will depend on their toxicity against normal cells.

This study examines the effect of phycoerythrin (PE) from a cyanobacterial Nostoc strain encapsulated with alginate as a potential prebiotic to produce synbiotic ice cream products with Lactobacillus casei . It was found that the addition of the encapsulated PE affected, mostly favourably, the physicochemical properties, antioxidant activity, probiotic survival, volatile compound contents, and sensory acceptability of the synbiotic ice cream samples before and after aging at the freezing periods of one day to eight weeks. Thus, it confirms the prebiotic potential of PE for synbiotic ice creams with L. casei .

The biological synthesis of nanoparticles (NPs) has become a new methodology for the eco-friendly production of NPs with high scalability and biocompatibility. Cyanobacteria are one of the most widespread microorganisms on Earth and have been proven to be successful biofactories for synthesizing NPs. It is challenging to discover new microalgae with the potential to synthesize NPs of small size with high stability.PurposeThe biological synthesis of nanoparticles (NPs) has become a new methodology for the eco-friendly production of NPs with high scalability and biocompatibility. Cyanobacteria are one of the most widespread microorganisms on Earth and have been proven to be successful biofactories for synthesizing NPs. It is challenging to discover new microalgae with the potential to synthesize NPs of small size with high stability.Nostoc muscorum Lukesova 2/91 was isolated, purified, and identified morphologically and genetically using microscopy and DNA sequencing. Volatile biomolecules in aqueous algal extracts were assessed using gas chromatography-mass spectroscopy (GC-MS).MethodsNostoc muscorum Lukesova 2/91 was isolated, purified, and identified morphologically and genetically using microscopy and DNA sequencing. Volatile biomolecules in aqueous algal extracts were assessed using gas chromatography-mass spectroscopy (GC-MS).Data showed that the main biomolecules were fatty acids and their esters, followed by secondary metabolites. Algal extract was used to convert silver nitrate (AgNO3) into silver NPs under various optimized parameters. 1 mM of AgNO3, 1:1 (V/V ratio of algal extract to AgNO3), 25 °C, under light illumination, for 24 h, at pH 7.4 were the optimum conditions for NP production (Nos@AgNPs). Nos@AgNPs were characterized using UV-VIS spectroscopy, FTIR, TEM, SEM, EDx, mapping, and a Zetasizer. The wavelength of Nos@AgNPs was 401.4 nm and their shapes were cubic to oval, with an average diameter of 11.8 ± 0.5 nm. FTIR spectroscopy revealed that proteins/polysaccharides could be the main reductants, whereas these molecules and/or fatty acids could be stabilizers for NP synthesis. Nos@AgNPs (86.15%) was silver and had a hydrodynamic diameter of 10.7 nm with a potential charge of -19.7 mV. Antiproliferative and antimicrobial activities of Nos@AgNPs were evaluated. Nos@AgNPs exhibited significant inhibitory activity against lung, colon, and breast cancer cells and considerable biocidal activity against Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia, and Pseudomonas aeruginosa.ResultsData showed that the main biomolecules were fatty acids and their esters, followed by secondary metabolites. Algal extract was used to convert silver nitrate (AgNO3) into silver NPs under various optimized parameters. 1 mM of AgNO3, 1:1 (V/V ratio of algal extract to AgNO3), 25 °C, under light illumination, for 24 h, at pH 7.4 were the optimum conditions for NP production (Nos@AgNPs). Nos@AgNPs were characterized using UV-VIS spectroscopy, FTIR, TEM, SEM, EDx, mapping, and a Zetasizer. The wavelength of Nos@AgNPs was 401.4 nm and their shapes were cubic to oval, with an average diameter of 11.8 ± 0.5 nm. FTIR spectroscopy revealed that proteins/polysaccharides could be the main reductants, whereas these molecules and/or fatty acids could be stabilizers for NP synthesis. Nos@AgNPs (86.15%) was silver and had a hydrodynamic diameter of 10.7 nm with a potential charge of -19.7 mV. Antiproliferative and antimicrobial activities of Nos@AgNPs were evaluated. Nos@AgNPs exhibited significant inhibitory activity against lung, colon, and breast cancer cells and considerable biocidal activity against Staphylococcus aureus, Escherichia coli, Klebsiella pneumonia, and Pseudomonas aeruginosa.N. muscorum Lukesova 2/91 is an excellent source for the biofabrication of small and stable AgNPs with potent inhibitory effects against cancer and bacterial cells.ConclusionN. muscorum Lukesova 2/91 is an excellent source for the biofabrication of small and stable AgNPs with potent inhibitory effects against cancer and bacterial cells.

The current investigation focuses on a systematic study of application of two dried algal biomass (i.e., Nostoc sp. and Turbinaria vulgaris ) in removal of Cr(VI) from synthetic solution as well as tannery industrial wastewater. The optimized conditions for Cr(VI) removal are nearly same for the both the biosorbents (i.e., pH 2.8, initial Cr(VI) concentration 100 mg L −1 , biomass dosage of 1.2g L −1 , contact time 120 and 110 min). Nostoc sp. ( q max =23.94mg g −1 ) was observed to possess a superior removal capability when compared to Turbinaria vulgaris ( q max =21.8mg g −1 ). Desorption studies were performed with four different desorbing agents. Application study was conducted using tannery wastewater with Nostoc sp . and 94.20% removal of Cr(VI) was obtained. Hence, this study revealed that Nostoc sp. and T. vulgaris both have great potential to be an environment friendly and economic biosorbent for removal of Cr(VI) containing industrial effluent. Graphical abstract

Cyanobacterial harmful algal blooms (CyanoHABs) represent a significant threat to freshwater ecosystems globally. To investigate the bacterial communities associated with these blooms, we conducted a metabarcoding analysis of water samples collected during the blooming events in various freshwater reservoirs, including Veeranam, Wellington, Perumal lake at Cuddalore and Trichy Kottapattu Pond, Tamil Nadu, India. Utilizing Metabarcoding of 16S rRNA amplicon sequencing, we characterized the taxonomic composition of bacterial communities in freshwater reservoirs. Our study revealed the dominance of key phyla such as Proteobacteria, Bacteroidetes, Firmicutes, and Actinobacteria across all four freshwater reservoirs. Predominantly, the abundance of cyanobacterial genera, notably toxin-producing Microcystis sp. and Nostoc sp., were identified, which played a crucial role in driving cyanobacterial bloom formation. Multifaceted interactions between bacteria and cyanobacteria, including core microbiomes and beta diversity patterns, shed light on the microbial dynamics underlying CyanoHABs. This provides a comprehensive understanding of freshwater reservoir Cyanobacterial dynamics, highlighting the bacterial communities involved in bloom events. These findings are crucial for protecting freshwater ecosystems and public health from the harmful effects of cyanobacterial blooms.

Cyanobacterial phycobiliproteins, such as phycoerythrin (PE) and phycocyanin (PC), are colored potential bioactive proteins that have antioxidant and antimicrobial properties. In this study, we formulated a new food prototype based on PE and PC-fortified low-fat yogurt and cream cheese. Four distinct low-fat yogurt and cream cheese products were manufactured, including a control group (No PE and PC), samples produced with phycoerythrin (+ PE), samples produced with phycocyanin (+ PC), and samples produced with both phycoerythrin and phycocyanin (PC + PE). Afterwards statistically compared the physicochemical composition, colorimetric properties, antioxidant and antimicrobial activities, and sensory profile of the fortified foods at 4 °C and 8 °C for 28 and 42 days. Additionally, we confirmed that PE and PC are not toxic to Caenorhabditis elegans at concentrations up to 1 mg/mL. The results showed that the MIC of PE and PC against E. coli was significantly higher than against S. aureus (3.12 ± 0.05 µg/mL vs. 1.56 ± 0.01 µg/mL, respectively; p  ≤ 0.05). Additionally, the maximum diameter of the inhibition zone of PE and PC against S. aureus was significantly higher than against E. coli (6.6 ± 0.011 mm vs. 11.66 ± 0.02 mm, respectively; p  ≤ 0.05). Results of color parameters showed that the control group had significantly higher L* values than the samples enriched with PE and PC. Moreover PE and PC significantly increased the a* and b* values respectively. The amount of ΔE in the control yogurts and cream cheese was higher than in the samples with PE and PC. Overall, the results showed that adding PE and PC had a significant effect on all measured factors ( p  < 0.01). Cream cheeses and low-fat yogurts enriched with either PE or PE + PC had the greatest antioxidant activity and the lowest number of psychrophilic bacteria and mold, and yeast counts at the end of the test period. Therefore, low-fat yogurt and cream cheese containing cyanobacterial PE and PC can be considered an innovative dairy product for the food industry. This study marks the initial effort to employ PE and PC derived from Nostoc sp. and Spirulina sp. as antioxidant and antimicrobial agents in the food industry.