Abstract
Lacticaseibacillus casei, Lacticaseibacillus chiayiensis, and Lacticaseibacillus zeae are very closely related Lacticaseibacillus species. L. casei has long been proposed as a probiotic, whereas studies on functional characterization for L. chiayiensis and L. zeae are some compared to L. casei. In this study, L. casei FBL6, L. chiayiensis FBL7, and L. zeae FBL8 were isolated from raw milk, and their probiotic properties were investigated. Genomic analysis demonstrated the role of L. chiayiensis and L. zeae as probiotic candidates. The three strains were tolerant to acid and bile salt, with inhibitory action against pathogenic bacterial strains and capacity of antioxidants. Complete genome sequences of the three strains were analyzed to highlight the probiotic properties at the genetic level, which results in the discovery of genes corresponding to phenotypic characterization. Moreover, genes known to confer probiotic characteristics were identified, including genes related to biosynthesis, defense machinery, adhesion, and stress adaptation. The comparative genomic analysis with other available genomes revealed 256, 214, and 32 unique genes for FBL6, FBL7, and FBL8, respectively. These genomes contained individual genes encoding proteins that are putatively involved in carbohydrate transport and metabolism, prokaryotic immune system for antiviral defense, and physiological control processes. In particular, L. casei FBL6 had a bacteriocin gene cluster that was not present in other genomes of L. casei, resulting in this strain may exhibit a wide range of antimicrobial activity compared to other L. casei strains. Our data can help us understand the probiotic functionalities of the three strains and suggest that L. chiayiensis and L. zeae species, which are closely related to L. casei, can also be considered as novel potential probiotic candidate strains.
Highlights
MATERIALS AND METHODSProbiotics are defined as live microorganisms that benefit host health when ingested in adequate amounts (Ye et al, 2020)
The complete genomes of L. chiayiensis FBL7 and L. zeae FBL8 contained a chromosome of 2,855,405 bp with a GC content of 47.2% and a chromosome of 3,132,522 bp with a GC content of 47.8%, respectively
This study was conducted to demonstrate the probiotic properties of L. casei FBL6, L. chiayiensis FBL7, and L. zeae FBL8 isolated from raw milk
Summary
Probiotics are defined as live microorganisms that benefit host health when ingested in adequate amounts (Ye et al, 2020). In this study, we investigated a phenotypic assay for L. casei FBL6, L. chiayiensis FBL7, and L. zeae FBL8 and identified related genes that are responsible for their probiotic properties. For the isolation of lactic acid bacterial strains, the serially diluted milk samples were spread on an MRS agar plate (Difco, Becton & Dickinson, Sparks, MD, United States) and incubated at 37◦C for 48 h under anaerobic conditions. Genomic DNA of the presumptive Lacticaseibacillus strain was extracted using the DNeasy Blood & Tissue Kits (Qiagen, Hilden, Germany) following the manufacturer’s protocol to identify isolates. For the comparative genomic analysis, publicly available genome sequences of L. casei, L. chiayiensis, L. zeae, and other reported Lacticaseibacillus species, L. paracasei, and L. rhamnosus, were downloaded from the NCBI database (Table 1).
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