The c group of Gram-negative gliding bacteria, has a long history of cosmopolitan occurrence. It has great biodiversity despite the absence of sexual reproduction. This wide biodiversity may be reflected in the wide spectrum of its secondary metabolites. These cyanobacterial secondary metabolites are biosynthesized by a variety of routes, notably by non-ribosomal peptide synthetase or polyketide synthetase systems, and show a wide range of biological activities including anticancer, antibacterial, antiviral and protease inhibition activities. This high degree of chemical diversity in cyanobacterial secondary metabolites may thus constitute a prolific source of new entities leading to the development of new pharmaceuticals.

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Cyanobacteria: an emerging source for drug discovery

Cyanobacteria and algae having complex photosynthetic systems can channelize absorbed solar energy into other forms of energy for production of food and metabolites. In addition, they are promising biocatalysts and can be used in the field of “white biotechnology” for enhancing the sustainable production of food, metabolites and green energy sources such as biodiesel. In this review, an endeavour has been made to uncover the significance of various metabolites like phenolics, phytoene/terpenoids, phytols, sterols, free fatty acids, photoprotective compounds (MAAs, scytonemin, s, polysaccharides, halogenated compounds, etc.), phytohormones, cyanotoxins, biocides (algaecides, herbicides and insecticides) etc. Apart from this, the importance of these metabolites as antibiotics, immunosuppressant, anticancer, antiviral, anti-inflammatory agent has also been discussed. Metabolites obtained from cyanobacteria and algae have several biotechnological, industrial, pharmaceutical and cosmetic uses which have also been discussed in this review along with the emerging technology of their harvesting for enhancing the production of compounds like bioethanol, biofuel etc. at commercial level. In later sections, we have discussed genetically modified organisms and metabolite production from them. We have also briefly discussed the concept of bioprocessing highlighting the functioning of companies engaged in metabolites production as well as their cost effectiveness and challenges that are being addressed by these companies.

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Uncovering Potential Applications of Cyanobacteria and Algal Metabolites in Biology, Agriculture and Medicine: Current Status and Future Prospects

Leaf surfaces (phyllospheres) have been shown to provide appropriate conditions for colonization by microorganisms including diazotrophic bacteria that are able to fix atmospheric nitrogen (N(2)). In this study, we determined leaf-associated N(2) fixation of a range of rainforest plants in Costa Rica, under different environmental conditions, by tracing biomass N incorporation from (15)N(2). N(2)-fixing bacterial communities of the plant species Carludovica drudei, Grias cauliflora and Costus laevis were investigated in more detail by analysis of the nifH gene and leaf-associated bacteria were identified by 16S rRNA gene analysis. N(2) fixation rates varied among plant species, their growth sites (different microclimatic conditions) and light exposure. Leaf-associated diazotrophic bacterial communities detected on C. drudei and C. laevis were mainly composed of cyanobacteria (Nostoc spp.), whereas on the leaves of G. cauliflora gamma-proteobacteria were dominant in addition to cyanobacteria. The complexity of diazotrophic communities on leaves was not correlated with N(2) fixation activity. 16S rRNA gene sequence analysis suggested the presence of complex microbial communities in association with leaves, however, cyanobacteria showed only low abundance. Our findings suggest that cyanobacteria as well as gamma-proteobacteria associated with leaf-colonizing epiphytes may provide significant nitrogen input into this rainforest ecosystem.

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Nitrogen fixation by phyllosphere bacteria associated with higher plants and their colonizing epiphytes of a tropical lowland rainforest of Costa Rica.

Cyanobacteria (blue-green algae) are Gram-negative oxygenic photosynthetic prokaryotes with a long evolutionary history. They have potential applications in diverse areas, especially in agriculture, as nutrient supplements in agriculture and industry (as biofertilizer, plant growth promoting rhizobacteria and as biocontrol agents). Their role as food supplements/nutraceuticals and in bioremediation and wastewater treatment is an emerging area of interest. In addition, they are known to produce wide array of bioactive compounds (secondary metabolites) with diverse biological activities — including antiviral, antibacterial, antifungal, antimalarial, antitumoral and anti-inflammatory properties, having therapeutic, industrial and agricultural significance. One of the major problems has been regarding their classification being incongruent with the phylogeny, because the phenotype of cyanobacterial strains is known to be altered under different environmental/nutritional conditions. However, because of their simple growth needs, they are the favourite model organisms for deeper understanding of several metabolic processes and for the production of recombinant compounds of medicinal and commercial value. In recent years, cyanobacteria have gained interest for producing third generation biofuels (both biomass and H2 production). With the recent advances in metabolic engineering techniques and availability of genome sequences, novel approaches are being explored for realising the potential of cyanobacteria. Our review provides an overview of the polyphasic approaches used in the analyses of cyanobacterial biodiversity and the potential of these organisms in providing viable solutions to global problems of food, energy and environmental degradation, which need further impetus through adoption of multidisciplinary collaborative programs.

New insights into the biodiversity and applications of cyanobacteria (blue-green algae)—Prospects and challenges

Five new antibacterial ambiguine K−O isonitriles (1−5) and eight previously described indole alkaloids were isolated from the cultured cyanobacterium Fischerella ambigua (UTEX 1903) by bioassay-guided fractionation. The planar structures of the new compounds were determined by spectroscopic analysis including MS and 1D and 2D NMR. X-ray crystallography was used to determine the absolute stereoconfiguration of ambiguine K isonitrile. The isolates were evaluated for their antibacterial activities against a set of bacterial targets, including Mycobacterium tuberculosis and Bacillus anthracis. Ambiguine K and M isonitriles showed the most potent activity against M. tuberculosis, with MIC values of 6.6 and 7.5 μM, respectively. Ambiguine A isonitrile showed the most potent activity against B. anthracis, with a MIC of 1.0 μM.

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Antimicrobial ambiguine isonitriles from the cyanobacterium Fischerella ambigua.

The active principle in a methanolic extract of the laboratory-grown cyanobacterium, Fischerella sp. isolated from Neem (Azadirachta indica) tree bark was active against Mycobacterium tuberculosis, Enterobacter aerogenes, Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella typhi, Escherichia coli as well as three multi-drug resistant E. coli strains in in vitro assays. Based on MS, UV, IR 1H NMR analyses the active principle is proposed to be hapalindole T having the empirical formula C21H23N2ClSO and a molecular weight of 386 with the melting point range 179–182 °C. The estimated production of Hapalindole T from the cyanobacterium is 1.25 mg g−1 lyophilized biomass. It is suggested that cyanobacteria colonizing specialized niches such as tree bark could be an antibacterial drug resource.

Identification of an antimicrobial entity from the cyanobacterium Fischerella sp. isolated from bark of Azadirachta indica (Neem) tree

The present study was aimed at the isolation, purification and structural elucidation of an antibacterial entity/lead molecule from the Antarctic cyanobacterium Nostoc CCC 537. A methanolic extract of the cyanobacterium was bioassayed with Enterobacter aerogenes as a target. The extract was purified by TLC, and the most active band was subjected to HPLC. The fraction (retention time 15.7 min) designated as the active principle was antibacterial towards Gram positive Mycobacterium tuberculosis H37Rv, Staphylococcus aureus ATCC 25923, Gram negative Salmonella typhi MTCC 3216, Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25992, Enterobacter aerogenes MTCC 2822 and multi-drug resistant strains of Escherichia coli GS 2003/01, 02, 03. Based on UV, IR, 1H NMR, EIMS, and ESIMS data, the structure of the active principle is proposed as 4-[(5-carboxy-2-hydroxy)-benzyl]-1,10-dihydroxy-3,4,7,11,11-pentamethyloctahydrocyclopenta naphthalene (Mr 428, Mp 243–249°C). This intracellular biomolecule is similar to anthraquinone and indane derivatives of a diterpenoid. The rate of production of the active principle currently corresponds to 1.70 mg g−1 biomass dry weight. The inherent property of Nostoc sp. to synthesise niche-specific biomolecules/lead molecules may be exploited for future drug development.

Deepali

Papers

Identification of an antimicrobial entity from the cyanobacterium Fischerella sp. isolated from bark of Azadirachta indica (Neem) tree

Isolation and identification of a new antibacterial entity from the Antarctic cyanobacterium Nostoc CCC 537

“Potential of Organic Amendments (AM fungi, PGPR, Vermicompost and Seaweeds) in Combating Salt Stress – A Review”

A deep learning-based integrative model for survival time prediction of head and neck squamous cell carcinoma patients

Structural and spectroscopic analysis of thermally stable Dy3+ activated Na4Ca4Si6O18 phosphor for optoelectronic device applications