Screening and Safety Assessment of a Lactobacillus sp. Strain with High Amylase Production

In order to identify a Lactobacillus sp. strain with efficient and safe in starch degradation, this study analyzed five distinct strains: Lactiplantibacillus plantarum JYI-3913 and AS1.555, Lactobacillus amylovorus CGMCC1.3395, Lactobacillus amylophilus CGMCC1.3394, and Lactobacillus paracasei CGMCC1.12731. The preliminary screening and re-screening for amylase production capabilities, the determination of enzyme production curve and growth curve were carried out to select the strain with the best ability to produce amylase. Subsequently, a detailed safety evaluation of the strain was carried out, including drug sensitivity test, drug resistance genetic testing, plasmid detection, hemolysis test, nitroreductase production, azoreductase production and amine production capacity detection, and acute oral toxicity test in mice. Results showed that, under the same culture conditions, the starch degradation transparent zone of L. amylovorus CGMCC1.3395 exhibited a clear transparent zone of starch degradation. Its starch degradation rate and amylase activity were 97.28% and 36.94 U/mL, respectively. And this strain displayed a relatively brief lag phase, while extending the log phase and stationary phase. Overall, this strain demonstrated superior integrated amylase production capabilities when compared to the other strains under investigation. In terms of antibiotic sensitivity, the selected strain exhibited sensitivity or intermediate sensitivity to the majority of the 22 tested antibiotics, with resistance observed for ampicillin, kanamycin, and four fluoroquinolone antibiotics. Moreover, this strain showed no associated drug-resistance genes and plasmids, thereby eliminating the risk of antibiotic-resistance gene transmission. It also lacked a hemolytic effect and did not produce potentially harmful metabolites such as nitroreductase, azoreductase, histamine, and tyramine. Mice displayed normal growth and weight gain over a 14 day feeding period, indicating the non-toxicity of the strain. In conclusion, L. amylovorus CGMCC1.3395 demonstrated a potent and safe capability for amylase production. These findings provide a theoretical foundation for the safe employment of this strain in the fermentation of starch-rich foods