Seasonal variation in chemical composition and antimicrobial activity of Asparagopsis armata from the southern Portuguese coast: Insights for biotechnological applications

The invasive alga Asparagopsis armata is a known threat to marine ecosystems; its abundant biomass and unique chemical properties, however, present opportunities for various biotechnological applications. This work focuses on the development of a green extraction method to produce A. armata extracts, the characterization of their volatile organic compounds (VOCs) content, and the assessment of their antimicrobial potential against a broad range of microorganisms, including Gram-positive and Gram-negative bacteria, filamentous fungi, and yeasts. Seasonal variations in the VOCs composition were found, with peaks in bioactivity corresponding to specific months of harvesting, displaying a bimodal pattern characterized by the increased accumulation of VOCs in spring and autumn. GC–MS chemical profiling revealed that the main VOCs present were halomethanes, among which bromoform was the major one, particularly in bioactive samples. Bromoform, however, at the concentrations observed in the hydrolates did not exhibit significant antimicrobial activity, suggesting the presence of possible synergistic interactions within the extracts. NMR analysis provided additional chemical fingerprint data of the samples, giving an overview of their composition and highlighting the presence of fatty acids. Our findings emphasize the potential of A. armata as a source of new bioactive compounds against human pathogens, while providing technical guidelines for the quick analysis and identification of bioactive water-based A. armata extracts. We strive to achieve and encourage sustainable harvesting and extraction strategies to mitigate the ecological impact of A. armata , transforming its invasiveness into a resource while promoting market value through bioprospecting and blue bioeconomy approaches. • First combined use of NMR, GC–MS, and bioactivity assays on A. armata extracts. • Seasonal extracts of A. armata showed variable antimicrobial bioactivity. • NMR analysis can distinguish hydrolates by bioactivity group. • GC–MS revealed halomethanes, especially bromoform, as dominant VOCs. • Bromoform is not solely responsible for the antimicrobial properties of the hydrolates.