Effects of brewer's yeast hydrolysate on the growth performance and the intestinal bacterial diversity of largemouth bass (Micropterus salmoides)

To investigate the effects of brewer's yeast hydrolysate (BYH) on the growth and intestinal bacteria diversity of largemouth bass (Micropterus salmoides)sthe fish were fed with basal diet supplemented with or without BYH (0, 0.1%, 0.2%) for 8 weeks. The results showed that the weight gain rate, survival rate, hepatosomatic index, organ coefficient and condition factor were not significantly different among the groups, except intraperitoneal fat ratio was significantly reduced in 0.2% BYH group. Totally 25 phyla, 56 classes, 103 orders, 155 families, 216 genera and 1051 operational taxonomic units (OTUs) of bacteria were identified from the 2,057,871 sequences obtained by Illumina MiSeq 16S rRNA sequencing. Among them, Fusobacteria, Firmicutes and Proteobacteria were the most three dominant phyla in the intestines regardless of diets. Furthermore, the richness of Fusobacteria, Cyanobacteria, Tenericutes and Actinobacteria in 0.2% BYH group was significantly lower than those of the control group. Interestingly, the ratio of Bacteroides/Firmicutes was decreased in the groups fed with BYH, this might be related to the modulations of energy absorption and storage, resulting in the decrease of fat deposition in fish body. At the genus level, several bacterial genera (Plesiomonas, Mycoplasmas, Synechococcus and Peptostreptococcus) which were potential pathogens of fish were significantly decreased in the groups fed with BYH. By contrast, a significant increase of Cetobacterium which could ferment peptides and carbohydrates to produce vitamin B12 was observed in fish fed with BYH, indicating that dietary BYH was helpful in propagation of some probiotic bacteria. Taken together, the overall intestinal bacterial diversity was decreased in fish fed with BYH which might promote the growth of some probiotics and inhibit some pathogenic bacteria, suggesting that BYH may serve as feed additive in modulation of the gut bacterial community of largemouth bass to decrease the potential pathogens.