Exploitation of waste biomass of the invasive alga species Rugulopteryx okamurae in Morocco: In-vitro antibacterial-antibiofilm properties and GC- MS metabolite profiling

Since 2017, the invasive brown alga Rugulopteryx okamurae has posed significant biological, ecological, and socio-economic challenges in Morocco due to its rapid proliferation and accumulation. This study explores its antimicrobial and antibiofilm properties and chemical composition. Methanol, chloroform, and ethyl acetate (EtOAc) extracts were evaluated for antibacterial activity against six human pathogens, including clinical and reference strains of Escherichia coli and Staphylococcus aureus . Fourier-transform infrared spectroscopy (FT-IR) identified functional groups such as hydroxyl (O-H), carbonyl (C = O), and polysaccharides, indicative of bioactive compounds. Gas chromatography-mass spectrometry (GC-MS) revealed key components: oleic acid butyl ester in the EtOAc extract, methyl tetradecanoate in the chloroform extract, and pentadecanoic acid methyl ester in the methanolic extract. The antibacterial potential was assessed using microdilution and growth curve assays, with minimal inhibitory and bactericidal concentrations ranging from 3.12–50 mg/mL. Growth curve analysis showed bacteriostatic effects through lag phase extension and growth rate suppression. The EtOAc extract demonstrated the highest antibiofilm activity, reducing biofilm formation by 73% in E. coli (clinical strain TT-23) and 70% in S. aureus (clinical strain 70). These results suggest that R. okamurae contains bioactive compounds with promising antibacterial and antibiofilm properties, potentially valuable for mitigating its impacts while offering applications in antimicrobial development.