Evaluation of Phytase Production by Fish Gut Bacterium, Bacillus subtilis, for Processing of Ipomea aquatica Leaves as Probable Aquafeed Ingredient

Abstract

Extracellular phytase production by Bacillus subtilis isolated from the gut of a minor carp, Labeo bata, has been investigated under solid-state fermentation using leaves from four low cost aquatic weeds (Ipomea aquatica, Pistia stratiotes, Lemna major, and Eichhornia crassipes) as substrates. Water spinach, I. aquatica, leaf meal supported maximum phytase activity (15.31 ± 0.38 U/g) and phytate degradation (66.79%). Incubation for 8 days at pH 7 and 35°C temperature revealed optimum phytase production. Maximum phytase production complied with 3.0-mL inoculum size (12.38 ± 0.05 U/g) and 60% initial moisture content (13.46 ± 0.08 U/g). Glucose (10 g/L) and ammonium sulfate (20.0 g/L) supplementation as additional carbon and nitrogen sources yielded maximum phytase production (12.24 ± 0.09 and 17.35 ± 0.06 U/g, respectively). Analysis of fermented leaf meal revealed that there was marginal increase (t-value significant at p < 0.05) in the contents of crude protein, lipid, minerals (Na, K, Ca, Mg, Zn, Fe, Cu, P), free amino acids, and fatty acids; along with reduction in the contents of the antinutritional factors—e.g., crude fiber, tannins, phytic acid, and trypsin inhibitor. The results indicate that there is ample scope for further research to appraise potential application of gut bacteria for sustainable utilization of aquatic weeds as aquafeed ingredients.

Keywords:

• fish gut bacteria
• phytase
• Ipomea aquatica
• Bacillus subtilis
• solid-state fermentation

Acknowledgments

The authors are grateful to the Head, Department of Zoology, The University of Burdwan, West Bengal, India; The Department of Science and Technology (FIST Program), New Delhi, India; and The University Grants Commission (UGC), New Delhi, India—Major Research Project F. No. 37–383/2009(SR)—for providing research facilities and financial support. The first author is grateful to the UGC for awarding the Junior Research Fellowship.