There are few studies on the intestinal microbiota of fish. The diversity of habitats and the varying nature of diets makes the symbiosis between fish and intestinal microorganisms diverse. The fish physiological processes, including metabolism and their immune system, are strongly influenced by microbiota. Recent studies have reported that immunostimulants are capable of modulating the intestinal microbiota of fish. β-glucan is among the most used and studied immunostimulants in animal husbandry, and has a chemical structure very similar to prebiotics. Thus, this study aimed to evaluate the bacterial intestinal composition of pacu Piaractus mesopotamicus fed with two different residual β-glucans from yeast (Saccharomyces cerevisiae) from sugarcane alcoholic fermentation.
To evaluate intestinal bacterial diversity, intestine samples were collected from 18 pacus (six per group) fed for 21 days with 1 g kg-1 diet containing 69.0% (group 1- G1), 56.4% (group 2- G2), or 0% (control group- CG) β-glucan. All fish were anesthetized in benzocaine (100 mg/mL), washed in running water, and sprayed with ethanol 70% prior to intestine sampling. The intestines were transferred to a 50 mL polyethylene tubes containing phosphate-buffered saline (PBS), Tween 80, methanol, tert-butanol, 20 glass microspheres, and vortexed for 1 minute before being centrifuged. The supernatant was transferred to sterile tubes and centrifuged. DNA was extracted from the precipitated material for 16S rRNA gene sequencing and metagenomic DNA library was constructed using the Illumina MiSeq platform.
There were no statistically significant differences between groups in the main identified bacterial genera. There was high prevalence of genera Cetobacterium (CG: 23.47%; G1: 24.50%; G2: 27.50%), Plesiomonas (CG: 18.93%; G1: 19.54%; G2: 18.98%), and Epulopiscium (CG: 13.25%; G1: 15.06%; G2: 15.55%) in all treatments, representing approximately 60% of all genera identified in the intestinal microbiota. The other 40% is distributed in genera with lower prevalence.
Acknowledgments: The authors would like to thank FAPESP (2013/50418-1) and CNPq (305007/2016-5 and 431713/2016-2) for financial support and Biorigin for the b-glucan donation and the intellectual support.