Gastrointestinal microbiota in Oreochromis mossambicus (Peters) and Oreochromis niloticus (Linnaeus): scanning electron microscopy and microbiological study

 

Author(s): Barnali Sarkar, Koushik Ghosh

Abstract: Gastrointestinal (GI) microbiota in two species of tilapia, Oreochromis mossambicus (Peters) and Oreochromis niloticus (Linnaeus) were evaluated in the present study.  Scanning electron microscopy (SEM) observation detected rod or round shaped bacteria associated with mucous and firmly attached to the intestinal mucosa. Distinct yeast colonies were also noticed either in the intestinal fold (microvilli) or with mucosa. Microbiological examination in different regions of the GI tract revealed that heterotrophic bacterial populations were the maximum in the hindgut regions in both the species. Further, proteolytic, amylolytic and cellulolytic bacterial populations were also detected abundantly within the GI tracts. Among different regions of the GI tract, protease and cellulase-producing bacterial community were the maximum in the hindgut regions; however, amylolytic population was the highest in foregut regions in both the fish species studied. Finally, on verification of the extracellular enzyme-producing capacity and considering dominance of bacteria within fish gut, three bacteria isolates, viz., OmM2, OmM3 and OnM1 were identified by 16SrDNA partial sequence analysis. Nucleotide blast in the NCBI GenBank revealed that the isolates OmM2 and OmM3 were belonged to Bacillus subtilis and Staphylococcus sp., respectively. The isolate OnM1 was considered as an uncultured bacterium clone. Further studies should be carried out to appraise the role of these autochthonous enzyme-producing microorganisms in vivo to explore their potential in commercial aquaculture.

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