Author(s): Dipanjan Dutta, Koushik Ghosh

Abstract: The present study was intended to screen autochthonous bacteria as novel probionts in mrigal, Cirrhinus mrigala. Altogether 117 extracellular enzyme-producing bacteria were isolated from the proximal (PI) and distal (DI) regions of the gut, out of which 30 strains were primarily selected through qualitative and quantitative assay of extracellular enzyme activities (viz., amylase, protease, lipase, cellulase, phytase, xylanase). Further, study of antagonism against 7 potential fish pathogens revealed 13 strains to be antagonistic against ≥1 pathogen(s) by cross-streaking and double-layer method. The strains CMH1X and CM2H3L, isolated from the DI region were capable of producing six studied extracellular enzymes and antagonistic to 5 tested fish pathogens. Both the strains were competent to grow in fish gut mucus and could resist fish bile juice (8%). Fingerlings of C. mrigala were intraperitoneally injected with thesernstrains separately and no mortality or external disease symptoms were noticed. Based on the results, the strains CMH1X and CM2H3L were selected as putative probiotics and identified as Bacillus amyloliquefaciens (KF623290) and Bacillus sonorensis (KF623291), respectively, through 16S rRNA partial gene sequence analysis. Although, the presently reported study depicts enzyme-producing capacity and antimicrobial potential of the gut bacteria in carps, in vivo studies are essential prior to their application in commercial aquaculture.

Pages: 310-318  |  1532 Views  129 Downloads

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