Ethanolic extracts from deep marine sponges: A new frontier in antibacterial discovery from the Jordanian Gulf of Aqaba

The urgent need for new antibiotics to counter bacterial resistance has led to renewed interest in marine natural products. The present study evaluated the antibacterial potential of ethanolic extracts from three deep-sea sponges: <i>Stelletta sp</i>., <i>Dactylospongia cf. elegans</i> (<i>D. cf. elegans</i>) and <i>Axinella sp</i>., which were collected from the Gulf of Aqaba off the coast of Jordan. Antibacterial activity was assessed against Gram-negative and Gram-positive bacteria using the well diffusion method, followed by determination of the Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC). Only <i>D. cf. elegans</i> exhibited potent activity, which was limited to Gram-positive bacteria and showed inhibition zones of 7 to 21 mm and MIC and MBC values of 1 and 2 mg/ml, respectively. <i>Stelletta sp</i>. showed no detectable activity, and <i>Axinella sp</i>. displayed minimal effects. DNA barcoding (28S rRNA) confirmed that all three species belong to the class Demospongiae. LC-MS/MS analysis of the extract from <i>D. cf. elegans</i> identified bioactive constituents, including bolinaquinone, dactyloquinone, gallic acid and caffeic acid, which are compounds known for antibacterial properties and likely contributed to the observed activity. Thus, <i>D. cf. elegans</i> could be a promising source of antibacterial agents against Gram-positive pathogens and warrants further evaluation of the mechanisms involved, its toxicity, and its effects <i>in vivo</i>.