Bioactive Compounds Derived from Marine Halophilic Bacteria: Studies on In Vitro and In Silico Docking

Halophilic marine bacteria have been considered for their potential secondary metabolites that possess antagonistic activity, bio-reducing activity, and a number of clinical and probiotic applications. In total, 12 halophilic bacterial strains were isolated from marine water and soil sediment samples. From the primary antimicrobial screening of the cell-free supernatant of all isolates, T7 and N5 strains showed significant results. The genomic DNA of these strains was isolated and their nucleotide sequencing confirmed as Vibrio alginolyticus (T7) and Aeromonas veronii (N5), respectively. The bacterial secondary metabolites from ethyl acetate extract (EAE) were tested against pathogens (Vibrio harveyi, Vibrio parahaemolyticus, Vibrio spp., and Aeromonas hydrophila). The Fourier transform infrared (FT-IR) characterization of the EAE revealed nine functional groups, primarily alkanes and amides, in each isolate (T7 and N5), while gas chromatography mass spectrometry (GC-MS) identified nine compounds from V. alginolyticus (T7) and four from A. veronii (N5). The molecular docking was performed for 12 compounds against proteins from pathogens: DNA gyrase subunit B and the topoisomerase IV (Topo IV), which revealed the potential binding mode of the ligands to the sites of the appropriate targets. Whereas the compound decyl phthalate from V. alginolyticus showed an active binding affinity value - 5.5 to - 6.6 kcal/mol against gyrB and Topo IV proteins of pathogens, compounds phthalic acid, 2-ethylhexyl pentadecyl ester, and bis(2-ethylhexyl) phthalate from A. veronii showed high binding affinity values of - 6.1 to - 7.2 and - 5.7 to - 6.8 kcal/mol against fish pathogen proteins of the gyrB protein and Topo IV, respectively. Thus, the protein with ligand binding affinity indicates a stronger inhibition of V. harveyi and A. hydrophila compared to other pathogens. Overall, the compounds from the EAE of A. veronii were found to be highly effective against pathogens compared to the EAE of V. alginolyticus. Therefore, further studies are needed to explore the potential therapeutic applications in treating bacterial infections in aquaculture settings.