Novel toxic metabolites from marine cyanobacteria have been thoroughly explored. Biologically active and chemically diverse compounds that could be hepatotoxic, neurotoxic or cytotoxic, such as cyclic peptides, lipopeptides, fatty acid amides, alkaloids and saccharides, have been produced from marine cyanobacteria. Many reports have revealed that biosynthesis of active metabolites is predominant during cyanobacterial bloom formation. Marine cyanobacterial toxic metabolites exhibit important biological properties, such as interfering in signal transduction either by activation or blockage of sodium channels or by targeting signaling proteins; inducing apoptosis by disrupting cytoskeletal proteins; and inhibiting membrane transporters, receptors, serine proteases and topoisomerases. The pharmacological importance of these metabolites resides in their proliferation and growth-controlling abilities towards cancer cell lines and disease-causing potent microbial agents (bacteria, virus, fungi and protozoa). Besides their toxic and pharmacological potentials, the present review discusses structural and functional resemblance of marine cyanobacterial metabolites to marine algae, sponges and mollusks.

Synthesis of silver nanoparticles by cell-free extract (CFE) of Pseudomonas aeruginosa M6 isolated from a mangrove ecosystem was demonstrated using two physical methods, namely, boiling (conventional thermal treatment (CTT)) and microwave treatment (MWT) at pH 9. X-ray diffraction (XRD) analysis revealed the presence of smaller (10.4 nm), pure silver nanoparticles synthesized via CTT (C-NPs) and larger silver oxide nanoparticles in majority with negligible concentration of pure silver particles by MWT. Transmission electron microscopy (TEM) analysis showed that C-NPs are spherical in shape. Atomic force microscopy (AFM) analysis also confirmed the presence of large-sized, aggregated nanoparticles synthesized via MWT (M-NPs). Electrophoresis indicated the size and charge-based mobility in agarose gel (0.4%), wherein the C-NPs moved faster than M-NPs, because of their relatively smaller size. The zeta potential value of C-NPs and M-NPs was found to be −30.1 mV and −23.1 mV, respectively. Fourier transform infrared (FT-IR) results revealed that both C-NPs and M-NPs were capped with proteins, but with different conformations. Furthermore, TEM analysis of bacterial cells exposed to aqueous silver nitrate showed the presence of spherical silver nanoparticles accumulated in periplasmic space, indicating the possible involvement of periplasmic nitrate reductase in this process. In addition, both C-NPs and M-NPs have also shown good antibacterial and anticandidal activities. Thus, marine Pseudomonas aeruginosa M6 can be a potential source for the synthesis of silver nanoparticles.

Two cobalt(III) Schiff base complexes, trans-[Co(salen)(DA) 2 ](ClO 4 ) ( 1 ) and trans-[Co(salophen)(DA) 2 ](ClO 4 ) ( 2 ) (where salen: N,N’-bis(salicylidene)ethylenediamine, salopen: N,N’-bis(salicylidene)-1,2-phenylenediamine, DA: dodecylamine) were synthesised and characterised using various spectroscopic and analytical techniques. The binding affinity of both the complexes with CT-DNA was explored adopting UV-visible, fluorescence, circular dichroism spectroscopy and cyclic voltammetry techniques. The results revealed that both the complexes interacted with DNA via intercalation as well as notable groove binding. Protein (BSA) binding ability of these complexes was investigated by absorption and emission spectroscopy which indicate that these complexes engage in strong hydrophobic interaction with BSA. The mode of interaction between these complexes and CT-DNA/BSA was studied by molecular docking analysis. The in vitro cytotoxic property of the complexes was evaluated in A549 (human small cell lung carcinoma) and VERO (African green monkey kidney cells). The results revealed that the complexes affect viability of the cells. AO and EB staining and cell cycle analysis revealed that the mode of cell death is apoptosis. Both the complexes showed profound inhibition of angiogenesis as revealed in in-vivo chicken chorioallantoic membrane (CAM) assay. Of the two complexes, the complex 2 proved to be much more efficient in affecting the viability of lung cancer cells than complex 1 . These results indicate that the cobalt(III) Schiff base complexes in this study can be potentially used for cancer chemotherapy and as inhibitor of angiogenesis, in general, and lung cancer in particular, for which there is need for substantiation at the level of signalling mechanisms and gene expressions.

Freshwater and terrestrial cyanobacteria resemble the marine forms in producing divergent chemicals such as linear, cyclic and azole containing peptides, alkaloids, cyclophanes, terpenes, lactones, etc. These metabolites have wider biomedical potentials in targeting proteases, cancers, parasites, pathogens and other cyanobacteria and algae (allelopathy). Among the various families of non-marine cyanobacterial peptides reported, many of them are acting as serine protease inhibitors. While the micropeptin family has a preference for chymotrypsin inhibition rather than other serine proteases, the aeruginosin family targets trypsin and thrombin. In addition, cyanobacterial compounds such as scytonemide A, lyngbyazothrins C and D and cylindrocyclophanes were found to inhibit 20S proteosome. Apart from proteases, metabolites blocking the other targets of cancer pathways may exhibit cytotoxic effect. Colon and rectum, breast, lung and prostate are the worst affecting cancers in humans and are deduced to be inhibited by both peptidic and non-peptidic compounds. Moreover, the growth of infections causing parasites such as Plasmodium, Leishmania and Trypanosoma are well controlled by peptides: aerucyclamides A-D, tychonamides and alkaloids: nostocarboline and calothrixins. Likewise, varieties of cyanobacterial compounds tend to inhibit serious infectious disease causing bacterial, fungal and viral agents. Interestingly, portoamides, spiroidesin, nostocyclamide and kasumigamide are the allelopathic peptides determined to suppress the growth of toxic cyanobacteria and nuisance algae. Thus cyanobacterial compounds have a broad bioactive spectrum; the analysis of SAR studies will not only assist to find out the mode of action but also reveal bioactive key components. Thereby, developing the drugs bearing these bioactive skeletons to treat various illnesses is wide open.

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A homologous series of 1-alkyl-(N,N-dimethylamino)pyridinium bromides, termed compounds 1-11, was synthesized and studied for antibacterial and antifungal activity. Of these, compound 8, containing a ten-carbon alkyl chain, showed maximum inhibition against all the tested bacterial strains. The highest antibacterial activity using a disc diffusion method was recorded against Mycobacterium smegmatis [zone of inhibition (ZOI): 45.75±0.25 mm], followed by Escherichia coli, Proteus mirabilis, Vibrio cholerae, Staphylococcus aureus and Salmonella typhi. In addition to antibacterial activity, compounds 3-11 displayed good inhibitory action against the human opportunistic yeast pathogens Cryptococcus neoformans and various Candida spp. The maximum ZOI was observed against Cryptococcus neoformans (51.5±0.5 mm) using compound 8, with ZOIs of 23.5±0.5, 32.0±0.0, 27.75±0.25 and 41.5±0.5 mm against Candida albicans, Candida glabrata, Candida tropicalis and Candida krusei, respectively. Furthermore, compound 8 caused inhibition of the candidal yeast-hyphae transition at a concentration of 0.29 mM and also inhibited the secretion of extracellular hydrolytic enzyme such as secreted aspartyl proteinase at subinhibitory concentrations. Compound 8 showed very little haemolytic activity at a concentration of 0.58 mM (1.315±0.75 %), with its highest haemolytic activity (47.806±2.32 %) observed at a concentration of 2.9 mM.

The fungal communities of different soil compartments in mangrove ecosystem are poorly studied. We sequenced the internal transcribed spacer (ITS) regions to characterize the fungal communities in Avicennia marina root-associated soils (rhizosphere and pneumatophore) and bulk soil compartments. The rhizosphere but not pneumatophore soil compartment had significantly lower fungal species richness than bulk soil. However, bulk soil fungal diversity (Shannon diversity index) was significantly higher than both pneumatophore and rhizosphere soil compartments. The different soil compartments significantly affected the fungal community composition. Pairwise sample analyses showed that bulk soil microbial community composition significantly different from rhizosphere and pneumatophore soil compartments. There was, however no significant difference observed between rhizosphere and pneumatophore soil fungal community composition and they shared relatively more OTUs between them. Further, there was a significant correlation observed between fungal community compositional changes and carbon or nitrogen availability of different soil compartments. These results suggest that few characteristics such as fungal richness and taxa abundance of rhizosphere and pneumatophore soil compartments were significantly different in mangrove ecosystem.

The opportunistic yeast pathogen Candida albicans and the emerging non-albicans Candida spp. cause life-threatening infections in immuno-compromised patients, leading to an increase in mortality rate. At present, the emergence of non-albicans Candida spp. causes serious infections that are difficult to treat the human populations worldwide. The available, synthetic antifungal drugs show high toxicity to host tissues causing adverse effects. Many metabolites of terrestrial and marine plants, microbes, algae, etc., contain a rich source of unexplored novel leads of different types, which are under use to treat various diseases. Such natural drugs are less expensive and have lower toxicity to host tissues. The patent search on identified and potential anticandidal-lead molecules, from various patent databases, has been described in this review. Furthermore, this article consolidates the trends in the development of anticandidal drug discovery worldwide. Most of the investigations on natural, bioactive molecules against candidiasis are in various phases of clinical trials, of which, two drugs Caspofungin acetate and Micafungin sodium were approved by the U.S. FDA. In conclusion, the exploration of drugs from natural resources serves as a better alternative source in anticandidal therapeutics, having great scope for drug discovery in the future.