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Isolation and Screening on Antagonistic Secondary Metabolites from Seaweeds Surface Associate Bacterial Strains and In Vitro Pharmaceutical Approach
The present study explores the pharmaceutical potentials of marine bacterial strains isolated from the surface of seaweeds (macroalgae) collected from Kanyakumari coast of Tamilnadu. Totally six different seaweeds namely Chaetomorpha indica, Ulva fasciata (Red algae), Sargassum wightii, Padina gymnosperma (Brown algae) and Hypnea musciformis, Gracilaria edulis (Red algae) were collected and the total epiphytic bacterial isolates (CFU/g) on the surface of each seaweed species were assessed. Results on total epiphytic bacterial load revealed that they were in the following order: brown algae (19 to 23 x 105 CFU/g) < green algae (24 to 27 x 105 CFU/g) < red algae (30 to 37 x 105 CFU/g). Gram’s reaction of epiphytic bacterial strains inferred red algae possess equal proportion (50%) of gram positive and gram negative bacteria; nonetheless green and brown algae had higher percentage of gram positive rather than gram negative bacteria. Polyphasic characteristics showed presence of 19 different bacterial genera. Amongst which Bacillus sp. dominated higher percentage of occurrence (22 to 45.47%) in all the seaweed species. But other bacterial genera showed a consistent variation in its occurrence. Primary screening through cross- streak method inferred Bacillus sp., Pseudomonas sp., Alteromonas sp., Vibrio sp., Shigella sp., Pseudoalteromonas sp. and Shewanella sp. strongly deterred growth of all the human bacterial pathogens. Further to scrutinize and identify the potent bacterial strain (s), a secondary screening test was conducted using agar well diffusion method and it inferred that Pseudoalteromonas sp. (SW13) and Vibrio sp. (SW07) had profound antagonistic activity the other tested bacterial genera. Antibacterial assay using crude ethyl acetate extracts of both epiphytic bacterial strains indicated Pseudoalteromonas sp. had elevated inhibitory zone (23 to 27mm) than Vibrio sp. (13 to 19mm).
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