Characterization and identification of phytase-producing bacteria isolated from the gastrointestinal tract of four freshwater teleosts

Abstract

Isolation and enumeration of phytase-producing bacteria in the proximal intestine (PI) and distal intestine (DI) of four freshwater teleosts, Nile tilapia (Oreochromis niloticus), murrel (Channa punctatus), climbing perch (Anabas testudineus), and stinging catfish (Heteropneustes fossilis) have been carried out following enrichment culture technique. The bacterial isolates were screened on the basis of their phytase-producing ability. In modified phytase screening medium (MPSM), phytase-producing strains were recorded at higher densities in the PI of Nile tilapia and climbing perch and at a minimum in the DI of catfish. Out of 32 isolates, 20 phytase-producing strains (9 from the DI and 11 from the PI) were primarily selected on the basis of qualitative assay on MPSM plates. Among these isolates, 3 strains (2 from the PI and 1 from the DI) were selected as potent phytase producers according to quantitative enzyme assay. Maximum phytase activity was detected in the bacterial strain ONF2 isolated from the PI of O. niloticus followed by CPF6 and CPH6, isolated from the PI and DI, respectively of C. punctatus. All the three selected phytase-producing strains were Gram-positive rods, capable of forming endospores, and could tolerate a wide range of temperature (25-42 C) and pH (6-10). The strain CPF6 was able to grow at temperatures up to 55 C. On the basis of 16S rDNA sequence analysis, isolates ONF2, CPF6 and CPH6 were identified as Bacillus licheniformis. The strain ONF2 showed 100 % similarity to B. licheniformis strain LCR32 (Accession no. FJ976541.1) whereas CPF6 and CPH6 showed 99 % similarity to B. licheniformis strain LCR32 (Accession no. FJ976541.1). © 2013 Springer-Verlag Berlin Heidelberg and the University of Milan.