Abstract
This study shows the antibacterial activity of three selected brown marine algae from Al-Shuqaiq province's red sea coast, Saudi Arabia. The three selected algal species were identified as Sargassum denticulatum, Sargassum filipendula, and Padina gymnospora and evaluated for their potential antibacterial bioactivity against 11 isolates of bacteria isolated from the wastewater collected from swage station of Khamis Mushait area. Three different algal extracts were prepared using methanol, ethanol, and diethyl ether. All algal extracts prepared with the diethyl ether were the most effective among all solvents used for the preparation of extracts in this study. The diethyl ether extract for S. denticulatum followed by S. filipendula were the most effective targeted marine algae against wastewater isolated bacteria. The S. denticulatum diethyl ether extract gave the highest inhibition zone diameter (33, 45, and 25 mm) bacterial isolates 5b, 12b, and 14b, respectively. Therefore, the bacterial isolates 5b, 12b, and 14b subjected to identification based on sequencing and phylogenetic analysis of 16S rRNA gene. The phylogenetic analysis for the three isolates 5b, 12b, and 14b indicated that they are closely relative with Bacillus cereus, Bacillus amyloliquifaciens, and Chryseobacterium cucumeris, respectively. The major constituents of S. denticulatum diethy ether extract fraction were confirmed by gas chromatography-mass spectrometry (GC-MS) analysis, Fourier-transform infrared spectroscopy, and nuclear magnetic resonance (NMR) ((1) H and C-13-NMR) spectroscopy. A total of six fatty acid esters were recognized in S. denticulatum extract by the retention time and the fragmentation pattern data of GC/MS analysis. The identified fatty acid esters were, methyl 13-methyl pentadecanoate, methyl 9-(Z)-octadecenoate, methyl 15-methylheptadecanoate, 2,3-dihydroxypropyl 9-(Z)-octadecenoate, methyl 13-docosenoate, and 9-(Z)-octadecenyl hexadecanoate.