The Resistance Abilities of Some <i>Bacillus</i> Species to Gastrointestinal Tract Conditions: Whole Genome Sequencing of the Novel Candidate Probiotic Strains <i>Bacillus clausii</i><scp>BA8</scp> and <i>Bacillus subtilis</i><scp>BA11</scp>

This study aims to investigate the resistance of potential probiotic <i>Bacillus</i> species to various conditions in the gastrointestinal (GI) tract and their safety characteristics. MALDI-TOF MS identified all tested strains with a good safety score of ≥ 2.0; the strains demonstrated the capacity to pass through the Gl tract, exhibiting a reduction of > 6 log/CFU live cells. Furthermore, they exhibited varying survival rates in an acidic environment (pH 2.0-3.0) and the presence of Ox-Bile (1% w/v) (<i>p</i> < 0.05). Following exposure to pH 3.0 and Ox-Bile, the survival rate of <i>Bacillus</i> spp. ranged between 85.94% and 91.24% and 87.30% and 91.54%, respectively. The results of the in vitro experiments showed that the six <i>Bacillus</i> strains had comparable characteristics (e.g., tolerance to GI track enzyme, auto-aggregation ability) to the reference probiotic strain <i>Lactiplantibacillus plantarum</i> LA15. The auto-aggregation results of the <i>B. clausii</i> BA8 strain, which has demonstrated resistance to GI tract conditions, were also noteworthy. This strain showed 72.32% after 2 h and 74.55% at the end of 5 h. Most suitable for use as probiotic strains <i>B. clausii</i> BA8 and <i>B. subtilis</i> BA11, sequenced via Illumina NovaSeq, showed average nucleotide identity (ANI) values of 98.1% and 97.8%, respectively. The genome annotation of <i>B. clausii</i> and <i>B. subtilis</i> with Prokka revealed 4,498,248-4,215,606 bp genome length, 44%-43% GC content, and 110-26 contigs, respectively. <i>B. clausii</i> BA8 has been comprehensively characterized, is of low risk for human consumption, and has been recommended as a potential probiotic strain. However, further in vivo experimentation is required to confirm these findings.