Abstract
BackgroundThe physiology and application characteristics of probiotics are closely associated with the growth phase. Bifidobacterium animalis subsp. lactis A6 is a promising probiotic strain isolated from the feces of a healthy centenarian in China. In this study, RNA-seq was carried out to investigate the metabolic mechanism between the exponential and the stationary phase in B. lactis A6.ResultsDifferential expression analysis showed that a total of 815 genes were significantly changed in the stationary phase compared to the exponential phase, which consisted of 399 up-regulated and 416 down-regulated genes. The results showed that the transport and metabolism of cellobiose, xylooligosaccharides and raffinose were enhanced at the stationary phase, which expanded carbon source utilizing profile to confront with glucose consumption. Meanwhile, genes involved in cysteine-cystathionine-cycle (CCC) pathway, glutamate dehydrogenase, branched-chain amino acids (BCAAs) biosynthesis, and Clp protease were all up-regulated in the stationary phase, which may enhance the acid tolerance of B. lactis A6 during stationary phase. Acid tolerance assay indicated that the survival rate of stationary phase cells was 51.07% after treatment by pH 3.0 for 2h, which was 730-fold higher than that of 0.07% with log phase cells. In addition, peptidoglycan biosynthesis was significantly repressed, which is comparable with the decreased growth rate during the stationary phase. Remarkably, a putative gene cluster encoding Tad pili was up-regulated by 6.5 to 12.1-fold, which is consistent with the significantly increased adhesion rate to mucin from 2.38% to 4.90% during the transition from the exponential phase to the stationary phase.ConclusionsThis study reported growth phase-associated changes of B. lactis A6 during fermentation, including expanded carbon source utilizing profile, enhanced acid tolerance, and up-regulated Tad pili gene cluster responsible for bacterial adhesion in the stationary phase. These findings provide a novel insight into the growth phase associated characteristics in B. lactis A6 and provide valuable information for further application in the food industry.
Highlights
The physiology and application characteristics of probiotics are closely associated with the growth phase
Growth of B. lactis Bifidobacterium animalis subsp. lactis A6 (A6) strain In order to investigate the changes of growth situation, B. lactis A6 was cultured in 15 ml de Man-Rogosa-Sharp broth supplemented with 0.05% (w/v) L-cysteine (MRSc) for 24 h
Based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, the differential expression genes (DEGs) involved in carbohydrate uptake and metabolism, oligopeptides uptake, peptidoglycan biosynthesis, acid tolerance resistance and adhesion to mucin were discussed in detail as follows
Summary
The physiology and application characteristics of probiotics are closely associated with the growth phase. RNA-seq was carried out to investigate the metabolic mechanism between the exponential and the stationary phase in B. lactis A6. The viability of Lactobacillus rhamnosus GG was approximately 20 times higher at stationary phase than that of cells from the exponential phase [6]. The maximum adhesion ability of L. rhamnosus GG to Caco-2 cells at the early stationary phase was ten times higher than that of cells at the exponential phase [7]. It is noteworthy to investigate the growth phase-associated metabolic mechanisms in probiotics
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