The impact of Bacillus subtilis 18 isolated from Tibetan yaks on growth performance and gut microbial community in mice.

The purpose of this study was to evaluate the effects of Bacillus subtilis 18 (BS-18) isolated from free-ranging Tibetan yaks in high altitude regions of Tibet (3600 m) on growth performance and gut microbial community in mice. In this study, mice (15-day-old) were used as an animal model and raised under standard conditions. A total of 20 KM mice were divided equally into two groups: control group (feed and drink freely), experimental group (feed and drink freely + 1 × 109  CFU/day BS-18). The intestines (duodenum, jejunum, ileum, cecum) and organs (liver, spleen, kidney) were collected from all the mice at day 18 for high throughput sequencing and HE staining. During the whole experiment, the mice treated by BS-18 displayed no abnormal behavior or macroscopic lesions on dissection. Meanwhile, there were no pathological changes observed using HE staining compared with the control group. The results show that BS-18 isolated from Tibetan yaks was safe and could increase average daily gain (ADG) and reduce feed conversion ratio (FCR). Furthermore, supplementation with BS-18 could improve the mucosal morphology and the ratio of villi to crypt cells (P < 0.05 or P < 0.01). The high-throughput sequencing results showed that the abundance and diversity of duodenum and jejunum in the experimental group were higher than control group. Lactobacillus in experimental group had higher abundance than control group. In addition, the quantity of Candidatus arthromitu was increased after BS-18 intake, which is associated with immune system activity. Acinetobacter induced brain abscess and bronchopneumonia were reduced in the experimental group. In conclusion, this study demonstrated that BS-18 isolated from Tibetan yaks was safe, beneficial and had the potential to serve as a probiotic.