Probiotic Potential of Bacillus licheniformis and Bacillus pumilus Isolated from Tibetan Yaks, China

Yak (Bos grunniens) inhabit an oxygen-deficient environment at the altitude of 3000 m on the Tibetan Plateau, with a distinctive gut micro-ecosystem. This study evaluated the probiotic potential and physiological property of Bacillus licheniformis and Bacillus pumilus isolated from the gut of yaks. Four strains, two Bacillus licheniformis (named D1 and D2) and two Bacillus pumilus (named X1 and X2), were isolated and identified by 16S rRNA sequencing. All strains had potential antibacterial ability against three indicator pathogens: Escherichia coli C83902, Staphylococcus aureus BNCC186335, and Salmonella enteritidis NTNC13349. The antioxidant activity test showed that D2 sample showed the highest antioxidant activity. Furthermore, all four strains had a higher hydrophobicity, auto-aggregation, acid tolerance, bile tolerance, and antibiotic sensitivity, which all contribute to their survival in the gastrointestinal tract and clinical utility. The animal experimentation (40 KM mice, equally divided into five groups of eight mice each) showed that the strain supplementation not only increased daily weight gain and reduced feed conversion ratio, but also increased the length of the jejunum villi and the value of the V/C (Villi/Crypt). In conclusion, this is the first study demonstrated the probiotic potential of Bacillus licheniformis and Bacillus pumilus isolated from yaks, providing a theoretical basis for the clinical application and development of new feed additives.