<i><span style="font-size:11.0pt;font-family: "Times New Roman";mso-fareast-font-family:"Times New Roman";mso-bidi-font-family: Mangal;mso-ansi-language:EN-GB;mso-fareast-language:EN-US;mso-bidi-language: HI" lang="EN-GB">recA</span></i><span style="font-size:11.0pt;font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";mso-bidi-font-family:Mangal; mso-ansi-language:EN-GB;mso-fareast-language:EN-US;mso-bidi-language:HI" lang="EN-GB">-based identification and antagonistic potential against fish pathogens by marine isolate DK1-SA11</span>

Abstract

In this study, marine isolate DK1-SA11 was identified and analyzed for antagonistic activity against fish pathogen along with its potential possible role as probiotic agent. The strain DK1-SA11 was identified on the basis of <i>rec-A</i> gene sequence similarity analysis and phylogenetic studies. Strain DK1-SA11 antagonistic activity against fish pathogens was analyzed by oxford cup agar diffusion method. Acute toxicity assay of strain DK1-SA11 with zebra fish <i>(Danio rerio)</i> was performed to evaluate the safety of strain for its future potential application as probiotic in aquaculture. <i>recA</i> gene sequencing analysis identified the strain as <i>Bacillus sbutilis</i> subsp. <i>spizizenii</i> strain DK1-SA11. Furthermore, strain DK1-SA11 has shown broad antagonistic activity against fish pathogens including <i>Aeromonas hydrophila</i>, <i>A. salmonicida</i>, <i>Vibrio alginolyticus</i>,

<i>V. anguillarum</i>, <i>V. campbellii</i>, <i>V. chagasii</i>, <i>V. chagasii</i>, <i>Photobacterium damsela</i>, <i>V. diazotrophicus</i>, <i>V. harveyi</i>, <i>V. ichthyoenteri</i>, <i>V. mediterranei</i>, <i>V. mimicus</i>, <i>V. parahaemolyticus</i>, <i>V. pomeroyi</i>, <i>V. splendidus</i>, <i>V. tubiashii</i>, <i>V. vulnificus</i> and <i>V. xuii</i>. Acute toxicity results revealed that strain has neither fatal nor visible toxic effect to fish and the lethal concentration (LC₅₀) of DK1-SA11 to the fish was > ¹⁰⁸ CFU mL^-1. Therefore, it has been concluded that <i>Bacillus subtilis</i> subsp. <i>spizizenii</i> strain DK1-SA11 might be a putative strain for prevention and control of fish and shellfish diseases, and could be use for probiosis.