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Finding alternative powerful antibacterial drugs of natural origins is, today, a crucial prerequisite due to the resistance of some bacterial strains to commercial and widely-used medications. Algae are characterized by their bioactive constituents and have a wide spectrum of biotechnological aspects, particularly antibacterial implications. During this study, four concentrations (5, 10, 20, and 40 mg mL–1) of the Egyptian untapped green microalga Rhizoclonium hieroglyphicum (Chlorophyta) were prepared using the polar solvents ethanol, methanol, and acetone. The antibacterial activity of the above-mentioned extracts was assessed, using the agar disc diffusion technique against three pathogenic bacteria, Staphylococcus aureus ATCC 6538, Escherichia coli ATCC 8739, and Pseudomonas aeruginosa ATCC 9027, which was compared to standard antibiotics. The minimal inhibitory concentrations (MICs) were also assessed and determined using a broth dilution assay. Our findings revealed that the R. hieroglyphicum ethanolic extract exhibited the most potent antibacterial effect and its MICs values were 0.533, 2.25, and 5.34 mg mL–1 against P. aeruginosa, E. coli, and S. aureus, respectively. A gas chromatography–mass spectrometry (GC–MS) approach to the crude R. hieroglyphicum ethanolic extract uncovered 30 different bioactive constituents, mainly including long-chain polyunsaturated and saturated fatty acids such as myristic (C14:0), palmitic (C16:0), stearic (C18:0), α-linolenic (C18:3; ω–3), and oleic (C18:1, ω–9) acids, which synergistically make this potent antibacterial action. The mechanism of action of these fatty acids was also discussed. Conclusively, R. hieroglyphicum could be a good candidate for the production and development of promising antibacterial agents. [ABSTRACT FROM AUTHOR]

Microalgae and cyanobacteria are rich sources of numerous phytochemical compounds with intrinsic antifungal potential. This research aimed to screen the phytochemical compounds and contents, as well as the antioxidant profiles, in eight cyanobacterial and two microalgal strains isolated from soil and brackish water habitats in Egypt. Our study also evaluated their antifungal activities against three phytopathogenic fungi—namely, Pythium ultimum, Fusarium solani, and Botryodiplodia theobromae, which are known to cause severe plant loss. The biochemical compounds were obtained from the cyanobacterial and algal methanolic extracts, and were identified through comparative phytochemical analyses related to the inhibition of the fungal pathogens. Comparative qualitative analyses of alkaloids, steroids, glycosides, and saponins were also carried out. The quantitative phytochemical screening of the cyanobacterial and algal strains investigated revealed the presence of xylanase, glucanase, and chitinase enzymes, along with some bioactive compounds, such as phenolics, flavonoids, proteins, neutral sugars, and carotenoids, which were species-dependent and detected in variable amounts in the extracts. The unicellular green microalgal strain Dunaliella sp. HSSASE13 displayed the highest level of antioxidant activity. However, the highest antifungal activities were shown by the heterocystous cyanobacterial strain Anabaena sp. HSSASE11 (83.94%), followed by Dunaliella sp. HSSASE13 (81.94%) and the non-heterocystous cyanobacterial strain Oscillatoria nigro-viridis HSSASE 15 (63.42%), against the three fungal pathogens B. theobromae, F. solani, and P. ultimum, respectively. Our results indicate that the highest significant and positive correlations of flavonoids (r = 0.854), phenolics (r = 0.785), DPPH scavenging activity (r = 0.876), total proteins (r = 0.808), xylanase activity (r = 0.876), glucanase activity (r = 0.746), and total neutral sugars (r = 0.764), in terms of their antifungal activities, were recorded against F. solani. Conclusively, the cyanobacterial and algal strains tested in the present study can be useful agents for the management and biocontrol of plant-infecting fungal pathogens. [ABSTRACT FROM AUTHOR]

Although a broad variety of classes of bioactive compounds have already been isolated from seaweeds of the genus Dictyota, most different species are still chemically and biologically unexplored. Dictyota species are well-known brown seaweeds belonging to the Dictyotaceae (Phaeophyta). The phytochemical composition within the genus Dictyota has recently received considerable interest, and a vast array of components, including diterpenes, sesquiterepenes, sterols, amino acids, as well as saturated and polyunsaturated fatty acids, have been characterized. The contribution of these valued metabolites to the biological potential, which includes anti-proliferative, anti-microbial, antiviral, antioxidant, anti-inflammatory, and anti-hyperpigmentation activities, of the genus Dictyota has also been explored. Therefore, this is the most comprehensive review, focusing on the published literature relevant to the chemically and pharmacologically diverse biopharmaceuticals isolated from different species of the genus Dictyota during the period from 1976 to now. [ABSTRACT FROM AUTHOR]