Probiotic characterization and spore production optimization of Lysinibacillus sp. MK212927

Members of the genus Lysinibacillus are increasingly explored as probiotic candidates, yet thorough screening and safety assessment remain essential due to the toxin-producing potential of related species. In this study, a soil-derived isolate, Lysinibacillus sp. MK212927 demonstrated strong antagonistic activity against multiple human enteropathogens and was selected for comprehensive characterization. The strain exhibited high resilience under physiologically relevant stress conditions, including low pH, simulated gastric and intestinal fluids, bile salts, and thermal exposure. It also displayed desirable probiotic attributes such as antioxidant capacity and bile salt hydrolase activity. Safety evaluation revealed the absence of hemolytic activity, minimal cytotoxicity toward Caco-2 cells, and susceptibility to vancomycin, levofloxacin, sulfamethoxazole, and doxycycline, with intermediate susceptibility to azithromycin and amoxicillin, suggesting a lack of plasmids or mobile genetic elements. To enhance its industrial applicability, response surface methodology (RSM) was applied to optimize biomass and spore production. Optimal conditions (pH 6.1, 33.5 °C, 200 rpm, and 0.21 vvm aeration) resulted in a 3.1-fold increase in biomass and a 5.4-fold increase in spore yield. In vivo assessment further showed that administration of Lysinibacillus sp. MK212927 improved body weight gain in rats, supporting its functional benefits as a feed supplement. Overall, the comprehensive phenotypic and safety evaluations highlight Lysinibacillus sp. MK212927 as a robust probiotic candidate with significant potential for controlling enteropathogens and for use in animal and human nutrition, warranting further preclinical and functional development. KEY POINTS: • Lysinibacillus sp. MK212927 exhibits strong inhibitory activity against human enteropathogens. • The strain tolerates low pH, bile salts, gastric and intestinal fluids, and heat, while displaying antioxidant and bile salt hydrolase activity. • Optimization of biomass and spore production, along with improved body weight in rats, supports its potential as a feed supplement.