Distribution of extracellular enzyme producing bacteria in the digestive tracts of four brackishwater 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). e heterotrophic bacterial population had the highest occurrence in the DI regions of all sh 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 identication. Both the strains SA2.2 isolated from S. argus and TJ2.3 isolated from T. jarbua showed high similarity to dierent strains of Brevibacillus parabrevis, while another strain, MG4.2, isolated from M. gulio, was similar to Bacillus licheniformis. e 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. e present study might oer scope for further research to evaluate prospects for application of the gut-associated extracellular enzyme-producing bacteria in brackish water aquaculture.