Chemical Composition, Antimicrobial Activity, and Molecular Docking of the Main Phytoconstituents from Three Rarely Investigated Marine Macroalgae

Objective: This study aimed to investigate the phytochemical and mineral compositions, antimicrobial activities, and molecular docking of 3 abundant and understudied seaweeds ( Cystoseira trinodis, Padina boryana, and Turbinaria triquetra). Methods: Extraction was performed using absolute ethanol, and chemical and mineral compositions were determined using the standard methods of the Association of Official Analytical Chemists. Total phenolics and flavonoids were assessed using the Folin-Ciocalteu and aluminum chloride methods, respectively. Chemical composition was screened using gas chromatography-mass spectrometry (GC-MS), and antimicrobial activity was evaluated using a disc diffusion assay. In addition, molecular docking analysis of the main compounds was performed. Results: The samples had high ash, carbohydrate, and fiber contents. The results showed high amount of Na, K, Mg, Ca, and Fe, with the highest values for Ca. Trace elements such as Cu, Mn, and Zn were found in low amounts in the studied species. The content of total phenolics ranged from 15.54 ± 0.1 to 39.5 ± 0.2 mg gallic acid equivalent/g. For flavonoid, it ranged from 3.4 ± 0.3 to 1.5 ± 0.2 mg rutin/g. GC-MS revealed 9 major compounds, mainly fatty acids, which have been reported to have antimicrobial activity. The antimicrobial results indicated a higher impact of the extracts against bacteria ( Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Proteus vulgaris) than against fungi ( Candida albicans and Aspergillus fumigatus), and a stronger dose-dependent effect against gram-positive ( B. subtilis and S. aureus) bacteria than against gram-negative bacteria ( E. coli and P. vulgaris). Molecular docking identified 1,2-benzenedicarboxylic acid mono(2-ethylhexyl) ester as the highest binding compound for penicillin-binding protein 6, suggesting its potential antimicrobial activity. Conclusion: These findings suggest that these seaweed species could serve as promising sources of functional foods with antimicrobial properties, with potential applications in the nutraceutical and pharmaceutical fields.