Isolation and characterization of bacterial strains from shoreline waters of Caspian Sea with novel antibacterial activity

In this study, a total ۱۰۸ bacterial strains with potential of antibacterial activity were isolated from ۱۴۵ shoreline water samples of Caspian Sea. The isolated bacteria were: Gram negative and positive bacilli, Gram negative and positive cocci and Gram negative coccoid. Amongst ۱۰۸ isolated bacterial strains, ۱۲ strains (۱۱%) showed significant antibacterial activity against ۱۰ reference strains. Morphological, physiological, biochemical features and ۱۶S rRNA analysis were used to identify the isolated strains with antibacterial activity. Amongst the isolated strains, six isolates possessed typical cellular, colonial morphologies, physiological, biochemical and nutritional features that resembled Bacillus spp. Four strains were identified as Bacillus cereus. The two other isolates belonged to Bacillus subtilis group. Two gram positive rod shape isolates were identified as Exiguobacterium acetylicum. The rest of isolates with antibacterial potency were gram negative bacteria. They were identified as Pseudomonas aeruginosa (۳isolate) and Alcaligenes faecalis (one isolate). Crude extracts of Pseudomonas aeruginosa strains showed significant antimicrobial activity against all reference strains. Also, E.acetylicum and A. faecalis showed antibacterial activity against some reference strains such as Escherichia coli PTCC ۱۵۳۳, Shigella flexneri PTCC ۱۲۳۴ and Salmonella enterica subsp.enterica Paratyphi B PTCC ۱۲۳۱. The crude extracts of four isolates with wide antibacterial activity were used in TLC autobiography overlay assay. The TLC autobiographic overlay assay implied that the antimicrobial metabolites produced by the strains with wide antimicrobial spectrum were different.

Keywords:

Caspian Sea , antibacterial activity , isolation , marine bacteria , Characterization