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Khan A., Ghosh K. 2012. Characterization and identification of gut-associated phytase-producing bacteria in some fresh water fish cultured in ponds. Acta Ichthyol. Piscat. 42 (1): 37-45.Background. Phytase produced by gut bacteria increases the availability of phosphorus and other important nutrients in ruminants by virtue of enzymatic hydrolysis of the phytic acid, an antinutritional factor present in the majority of plant feedstuffs. This topic, however, has been insufficiently investigated in fish. This study was intended: to evaluate the presence of phytase-producing autochthonous bacteria in the gastrointestinal (GI) tracts of 14 freshwater teleost fishes; and to identify the most promising phytase-producing strains by phenotypic characterization and 16S rDNA. Materials and methods. The GI tracts were removed and divided into proximal (PI) and distal (DI) intestine.Homogenates of intestinal segments were spread onto sterilized tryptone soya agar and modified phytase screening media (MPSM) plates to determine autochthonous culturable heterotrophic and phytase-producing microbiota, respectively. Data were presented as log viable counts (LVC) g-1 intestine. Out of 95 phytase-producing isolates, primarily selected 32 isolates were studied for phytase-assay using MPSM broth. Promising phytase-producing isolates were evaluated for other exo-enzymes (amylase, cellulase, protease, lipase) using 4 selective media. Two most promising phytase-producing isolates were identified by phenotypic characterization and 16S rDNA.Results. Population of heterotrophic bacteria was highest (LVC = 8.29 g -1 intestine) in the DI of Gudusia chapra followed by DI of Hypophthalmichthys molitrix (LVC = 6.82 g -1 intestine). However, more than log 4 reduction of the phytase-producing bacteria was observed compared to heterotrophic bacteria. Phytase-producing microbiota was highest in the PI of G. chapra (LVC = 3.95 g -1 intestine) followed by PI of Labeo calbasu (LVC = 3.78 g -1 intestine). The strain LB1.4 isolated from DI of Labeo bata showed highest phytase activity (2.33 ± 0.006 U · mL -1 ) followed by the strain GC1.2 (2.19 ± 0.018 U · mL -1 ) isolated from PI of G. chapra. Both isolates were efficient in producing other exo-enzymes. Phenotypic characterization and nucleotide homology analysis revealed that the isolates LB1.4 and GC1.2 were similar to Bacillus subtilis and Bacillus atrophaeus, respectively. Conclusion. Autochthonous phytate degrading bacteria were present in the GI tract of fish that might endow ecological advantages to overcome the anti-nutritional effects of plant phytate.Keywords: Gut bacteria, phytase, Bacillus, freshwater teleost, 16S rDNA During the last decade there has been an improved understanding on the importance of commensal intestinal microbiota in fish ). The gut microbiota may be categorized as either autochthonous (indigenous; adherent) or allochthonous (transient) depending upon its ability to adhere and colonize the mucus layer in the digestive tract (Ringø and Birkbeck 1999, Ringø et al. 2003). P...

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Antinutritional effects of phytic acid (myoinositol hexaphosphate, IP6) on growth and digestibility in fish have been reported. However, specific effect of IP6 on the digestive enzymes in fish has not been addressed. In this study, inhibitory effect of synthetic IP6 (Phytic acid sodium salt, 90% purity) on the activity of the digestive protease and α-amylase in rohu, Labeo rohita; catla, Catla catla; and mrigal, Cirrhinus mrigala has been investigated in vitro. Graded levels (12.5, 25, 50, 100, 150, and 200 μg/mL) of IP6 were added to the reaction mixtures containing enzyme extracts and substrate solution in triplicate to detect any change in enzyme activity. Results of the experiment revealed that IP6 significantly inhibit/lower activities of the digestive enzymes in a dose-dependent manner, as evident from the regression equations (F values significant at P < 0.001 level). Apparently, irrespective of the fish species studied IP6-induced inhibition of α-amylase activity was greater than protease activity. Among the three fish species studied, C. mrigala appeared to be more sensitive to IP6 for both α-amylase and protease activity. Enzyme activity was least affected in C. catla. Results of the study might raise concern while incorporating IP6 rich plant-derived feed ingredients in aqua feed preparation.

Isolation and enumeration of autochthonous heterotrophic gut microbiota from four carps (Labeo rohita, Catla catla, Hypophthalmichthys molitrix and Labeo bata) has been carried out. Gut isolates were analyzed qualitatively for extracellular amylase, protease, cellulase and lipase producing capacities and four superior isolates were further studied for phytase producing capabilities. The isolate CC1.1 (Rhodococcus sp. MTCC 9508) isolated from C. catla seemed to be the best phytase producer amongst the isolates studied. Bio-safety of the isolate was evaluated in vivo by injecting fresh broth culture to healthy laboratory acclimatized rohu, L. rohita. Presence of autochthonous phytase producing Rhodococcus sp. detected in the present study offers scope for further research to appraise its potential application in commercial aquaculture.