Assessment of the safety and probiotic properties of Lactobacillus delbrueckii DMLD-H1 based on comprehensive genomic and phenotypic analysis

Abstract

Lactobacillus delbrueckii is widely used in the fermentation industry. Previously, we identified Lactobacillus delbrueckii DMLD-H1, a strain of Lactobacillus delbrueckii subsp. bulgaricus, from traditional Chinese fermented milk. In this research, we sequenced the complete genome of DMLD-H1, which contains 1,836,627 bp in length with a total of 1947 genes and an average G + C content of 49.86%. In total, 103 carbohydrate metabolism genes are annotated in the KEGG database, and it is showed that DMLD-H1 has the ability to transport lactose, glucose, fructose, and mannose. Antibiotic resistance genes, genes encoding toxins and virulence factor genes are absent in risk-associated sequences of DMLD-H1. We also confirm its safety by indole assay, nitroreductase assay, and antibiotic resistance tests. A wide range of stress-related proteins may contribute to the survival of DMLD-H1 in the gastrointestinal environment, including oxidative stress, pH, bile salts, and temperature stress. The large number of adhesion proteins and stress response genes identified in DMLD-H1 in the genome-wide analysis, as well as phenotypic experiments including resistance to bile salts and acid, antioxidant, antimicrobial and self-cohesion activity, exhibited its excellent probiotic properties. This study demonstrates that DMLD-H1 can be a candidate fermentative agent in fermented dairy products.