Immunostimulatory activities of specific bacterial secondary metabolite of Anoxybacillus flavithermus strain SX‐4 on carp,Cyprinus carpio

Aims: To determine the capacity of secondary metabolite of strain SX‐4, to enhance the nonspecific immunity and survival of carp (Cyprinus carpio), and to identify the constituents that are responsible. Methods and Results: A thermophilic strain SX‐4 that 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 nonspecific immune responses and disease resistance (relative per cent 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‐1β and inducible nitric oxide synthase), in the blood were found to be significantly increased. Conclusions: The bacterial peptide cyclo‐(L‐Pro‐Gly) significantly enhances nonspecific immunity and survival of carp. Significance and Impact of the Study: 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.     

The use of probiotics in aquaculture

This study aims to present comprehensive notes for the use of probiotics in aquaculture. Probiotics have been proven to be positive promoters of aquatic animal growth, survival and health. In aquaculture, intestines, gills, the skin mucus of aquatic animals, and habitats or even culture collections and commercial products, can be sources for acquiring appropriate probiotics, which have been identified as bacteria (Gram‐positive and Gram‐negative) and nonbacteria (bacteriophages, microalgae and yeasts). While a bacterium is a pathogen to one aquatic animal, it can bring benefits to another fish species; a screening process plays a significant role in making a probiotic species specific. The administration of probiotics varies from oral/water routine to feed additives, of which the latter is commonly used in aquaculture. Probiotic applications can be either mono or multiple strains, or even in combination with prebiotic, immunostimulants such as synbiotics and synbiotism, and in live or dead forms. Encapsulating probiotics with live feed is a suitable approach to convey probiotics to aquatic animals. Dosage and duration of time are significant factors in providing desired results. Several modes of actions of probiotics are presented, while some others are not fully understood. Suggestions for further studies on the effects of probiotics in aquaculture are proposed.