Metabolome responses of Enterococcus faecium to acid shock and nitrite stress

Enhanced Cell Wall and Cell Membrane Activity Promotes Heat Adaptation of Enterococcus faecium

Enterococcus faecium (E. faecium) is widely used in foods and is known as a probiotic to treat or prevent diarrhea in pets and livestock. However, the poor resistance of E. faecium to high temperature processing procedures limits its use. Strain domestication is a low-cost and effective method to obtain high-temperature-resistant strains. In this study, heat treatment was performed from 45 °C to 70 °C and the temperature was gradually increased by 5 °C every 3 days. After domestication, the survival rates of the high temperature adaptation strain RS047-wl under 65 °C water bath for 40 min was 11.5 times higher than WT RS047. Moreover, the saturated fatty acid (SFA) contents in cell membrane and the cell volume significantly increased in the RS047-wl. The combined transcriptomic, metabolomic, and proteomics analysis results showed a significant enhancement of cell wall and membrane synthesis ability in the RS047-wl. In conclusion, one of the main factors contributing to the improved high temperature resistance of RS047-wl was its enhanced ability to synthesize cell wall and membrane, which helped maintain normal cell morphology. Developing a high-temperature-resistant strain and understanding its mechanism enables it to adapt to high temperatures. This lays the groundwork for its future development and application.

Enterococcus faecalis OG1RF Evolution at Low pH Selects Fusidate-Sensitive Mutants in Elongation Factor G and at High pH Selects Defects in Phosphate Transport

Enterococcus bacteria inhabit human and soil environments that show a wide range of pH values. Strains include commensals as well as antibiotic-resistant pathogens. We investigated the adaptation to pH stress in E. faecalis OG1RF by conducting experimental evolution under acidic (pH 4.8), neutral pH (pH 7.0), and basic (pH 9.0) conditions. A serial planktonic culture was performed for 500 generations and in a high-pH biofilm culture for 4 serial bead transfers. Nearly all of the mutations led to nonsynonomous codons, indicating adaptive selection. All of the acid-adapted clones from the planktonic culture showed a mutation in fusA (encoding elongation factor G). The acid-adapted fusA mutants had a trade-off of decreased resistance to fusidic acid (fusidate). All of the base-adapted clones from the planktonic cultures as well as some from the biofilm-adapted cultures showed mutations that affected the Pst phosphate ABC transporter (pstA, pstB, pstB2, pstC) and pyrR (pyrimidine biosynthesis regulator/uracil phosphoribosyltransferase). The biofilm cultures produced small-size colonies on brain heart infusion agar. These variants each contained a single mutation in pstB2, pstC, or pyrR. The pst and pyrR mutants outgrew the ancestral strain at pH 9.2, with a trade-off of lower growth at pH 4.8. Additional genes that had a mutation in multiple clones that evolved at high pH (but not at low pH) include opp1BCDF (oligopeptide ABC transporter), ccpA (catabolite control protein A), and ftsZ (septation protein). Overall, the experimental evolution of E. faecalis showed a strong pH dependence, favoring the fusidate-sensitive elongation factor G modification at low pH and the loss of phosphate transport genes at high pH. IMPORTANCE E. faecalis bacteria are found in dental biofilms, where they experience low pH as a result of fermentative metabolism. Thus, the effect of pH on antibiotic resistance has clinical importance. The loss of fusidate resistance is notable for OG1RF strains in which fusidate resistance is assumed to be a stable genetic marker. In endodontal infections, enterococci can resist calcium hydroxide therapy that generates extremely high pH values. In other environments, such as the soil and plant rhizosphere, enterococci experience acidification that is associated with climate change. Thus, the pH modulation of natural selection in enterococci is important for human health as well as for understanding soil environments.

Metabolome and microbiome alterations in tongue coating of gastric precancerous lesion patients

Objective: This paper seeks to provide mechanistic insight into the pathological transition through the analysis of metabolites and microorganisms in the tongue coating of gastric precancerous lesions (GPL) patients.Methods: GC-TOF-MS and UHPLC-QE-MS metabolomics, combined with 16S rRNA microbiome techniques, were performed to explore the changes in metabolites and microorganisms in the tongue coating of GPL patients.Results: When compared with 15 controls, 133 metabolites were found to be differentially expressed in 60 GPL cases, of which could be divided into ten categories. Among them, most of the differentially expressed metabolites identified were lipids or lipid-like molecules. These metabolites were implicated in 6 metabolic pathways including glycine, serine and threonine metabolism, arginine and proline metabolism, sphingolipid metabolism, valine, leucine and isoleucine degradation, arachidonic acid metabolism, and tyrosine metabolism. The relative abundances of Alloprevotella, Solobacterium, Rothia, Eikenella, and Aggregatibacter in the GPL group increased significantly relative to the controls and were associated with lipids and lipid-like molecules, organic nitrogen compounds, organic oxygen compounds, phenylpropanoids and polyketides, and organoheterocyclic compounds, respectively.Conclusions: Compared with healthy people, the changes of tongue coating metabolites in GPL patients were mainly characterized by alterations in lipid metabolism and were associated with localized changes in the microbiome.