A buffalo rumen-derived probiotic (SN-6) could effectively increase Simmental growth performance by regulating fecal microbiota and metabolism

Abstract Background: Microorganisms play a key role in rumen digestion which are often used as probiotics to promote growth in ruminants. However, it's unclear which bacteria play an important role and how they do it. This study focused on the growth-promoting effects of the buffalo-derived probiotic SN-6 and examined its effects on the fecal flora and metabolism in Simmental, analyzing the impact of altered intestinal flora on host metabolism to elucidate the underlying probiotic mechanisms.Results: Three bacterial strains, Bacillus pumilus (SN-3), Bacillus paralicheniformis (SN-6) and Bacillus altitudinis (SN-20) with multiple digestive enzymes secretion capability were isolated from the rumen of healthy Buffalo, SN-6 exhibited outstanding among the three strains. SN-6 secreted cellulase, laccase and amylase, and had potent inhibitory effects on Staphylococcus aureus ATCC25923 and Escherichia coli K99. In addition, SN-6 exhibited strong tolerance to artificial gastric juice, intestinal juice and high temperature. Antibiotic resistance test, virulence gene test and mouse toxicity test confirmed the safety of SN-6. SN-6 significantly increased the average daily weight gain of Simmental (p<0.01), and affects the fecal microbiota structure and fecal metabolomic patterns of Simmental. There was a remarkable difference in the β diversity of fecal microflora between SN-6 and control groups (p<0.05). Further, SN-6 significantly increased the abundance of Clostridium_sensu_stricto_1, Bifidobacterium, Blautia and Cellulolyticum and decreased the relative abundance of Monoglobus, norank_f_Ruminococcacea. Moreover, SN-6 feeding significantly enriched fecal metabolites to maintain intestinal homeostasis and strengthen intestinal barrier function (i.e., 3-Indoleacrylic acid, Kynurenic acid). Finally, the microbial and metabolic function analysis indicated that SN-6 would enhance amino acid metabolism (mainly tryptophan metabolism) and lipid metabolism pathways.Conclusions: SN-6 exerted beneficial effects by targeting the gut microbiota and host metabolism (mainly tryptophan metabolism). Our findings reveal the effect of SN-6 on Simmental microbiota and metabolism, and provide a new reference for the research on Bacillus regulating ruminant gut microbiota and metabolism.