Immunostimulatory Activities Of Specific Bacterial Secondary Metabolite Of Anoxybacillus Flavithermus Strain SX-4 On Carp, Cyprinus Carpio

To determine the capacity of secondary metabolite of strain SX-4, to enhance the non-specific immunity and survival of carp (Cyprinus carpio), and to identify the constituents that are responsible. A thermophilic strain SX-4 which is able to produce immunostimulatory metabolite was isolated from sludge sample of hot spring and identified by comparison with 16S rRNA sequences (99% of homology) as Anoxybacillus flavithermus. Bioactivity-guided fractionation of methanol extract from its cell-free culture, one bacterial peptide with the capacity of improving the non-specific immune responses and disease resistance (Relative percent survival= 66.67%) was obtained, and the compound was characterized as cyclo-(L-Pro-Gly) by IR, ESI-MS,1H NMR and 13C NMR spectroscopic analyses. After intraperitoneal administration of this peptide, selected innate immune parameters including phagocytic activity, superoxide anion production, serum lysozyme activity and serum SOD activity, along with immune-related genes expression (i.e. interleukin-1βand inducible nitric oxide synthase) in the blood were found to be significantly increased.The bacterial peptide cyclo-(L-Pro-Gly) significantly enhances non-specific immunity and survival of carp.There is a possibility of using cyclo-(L-Pro-Gly) as a better natural immunostimulant, which could have a promising role in aquaculture to prevent diseases and disease outbreaks.