Distribution of extracellular enzyme-producing bacteria in the digestive tracts of 4 brackish water fish species


Abstract: Occurrence and distribution of enzyme-producing bacteria in the proximal (PI), middle (MI), and distal (DI) segments of the gastrointestinal tracts of 4 brackish water teleosts (Scatophagus argus, Terapon jarbua, Mystus gulio, and Etroplus suratensis) have been investigated. Data were presented as log viable counts g^{-1} intestine (LVC). The heterotrophic bacterial population had the highest occurrence in the DI regions of all fish species studied except M. gulio. Proteolytic and amylolytic bacteria had the highest occurrence in the DI of M. gulio (LVC = 5.50 and 5.93, respectively), while cellulolytic and lipolytic populations exhibited highest occurrences in the DI regions of T. jarbua (LVC = 6.33) and S. argus (LVC = 5.78), respectively. Out of the 81 bacterial isolates, the most promising 3 isolates were determined through quantitative enzyme assay and studied through 16S rRNA gene sequence analysis for identification. Both the strains SA2.2 isolated from S. argus and TJ2.3 isolated from T. jarbua showed high similarity to different strains of Brevibacillus parabrevis, while another strain, MG4.2, isolated from M. gulio, was similar to Bacillus licheniformis. The NCBI GenBank accession numbers of the 16S rRNA gene sequences for isolates SA2.2, TJ2.3, and MG4.2 were KF377322, KF377324, and KF377323, respectively. The present study might offer scope for further research to evaluate prospects for application of the gut-associated extracellular enzyme-producing bacteria in brackish water aquaculture.

Keywords: Brackish water fish, gut bacteria, enzyme, Brevibacillus parabrevis

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