Enhancement of secondary metabolites from Bacillus Licheniformis XY-52 on immune response and expression of some immune-related genes in common carp, Cyprinus carpio

This study was undertaken to isolate active secondary metabolites from immunostimulatory Bacillus Licheniformis XY-52 and evaluate their activities at 0%, 0.5%, 1.0%, and 2.0% doses supplementation with feed on immune response in common carp at weeks 1, 2, and 3. By applying chromatography techniques and successive recrystallization, two purified metabolites were obtained and identified by spectral data (mass spectrometry and nuclear magnetic resonance) as: Cyclo-(Phe–Tyr) and Cyclo-(Phe–Gly). The results revealed that humoral innate immune parameters (lysozyme activity, phagocytic activity and bactericidal activity) were significantly (P