Analysis of Cyclocarya paliurus flavonoids modulation on the physiology and gene expression in Enterococcus faecalis under bile salt stress

Enterococcus faecalis is one of the probiotic groups in the intestinal tract which has varieties of functional effects in the host, such as a protective barrier, nutritional efficacy and antibacterial effects. Stress conditions such as low pH, bile salts, and hypertonicity are inevitable negative factors for the normal survival of E. faecalis in the gastrointestinal tract. Under the stress and inhibition of bile salt, E. faecalis needs specific adaptation and coping style if it wants to successfully colonize the intestine stably. The appropriate concentration of flavonoids can assist probiotics to serve a beneficial role and help them resist the stress of external irresistible environmental factors. In the present research, RNA-sequence (RNA-seq) technology was employed to investigate the influence of Cyclocarya paliurus flavonoids (CPF) on E. faecalis 131-2 (E. faecalis 131-2) exposed to bile salt stress. Analysis results revealed that under bile salt stress, many genes related to cellular process, catalytic activity and transport activity were significantly differentially expressed (P < 0·05), and some not expected variations of which could be partly alleviated by supplementation of CPF, indicating its capacity to improve the bile salt tolerances of E. faecalis 131-2. Additionally, CPF alleviated the obvious inhibitory effects of bile salt stress on the exponential growth of E. faecalis 131-2. An overall view of the physiological and transcriptomic changes of E. faecalis 131-2 under bile salt stresses with or without CPF will further deepen our understanding of the mechanism by which CPF assists E. faecalis 131-2 to perform beneficial functions in the gastrointestinal environment.