Metabolic responses to Lactobacillus plantarum contamination or bacteriophage treatment in Saccharomyces cerevisiae using a GC–MS-based metabolomics approach

Hexadecanoic acid produced in the co-culture of S. cerevisiae and E.coli promotes oxidative stress tolerance of the S.cerevisiae cells

Co-fermentation performed by Saccharomyces cerevisiae and Escherichia coli or other microbes has been widely used in industrial fermentation. Meanwhile, the co-cultured microbes might regulate each other's metabolisms or cell behaviors including oxidative stress tolerance through secreting molecules. Here, results based on the co-culture system of S. cerevisiae and E. coli suggested the promoting effect of E. coli on the oxidative stress tolerance of S. cerevisiae cells. The co-cultured E. coli could enhance S. cerevisiae cell viability through improving its membrane stability and reducing the oxidized lipid level. Meanwhile, promoting effect of the co-cultured supernatant on the oxidative stress tolerance of S. cerevisiae illustrated by the supernatant substitution strategy suggested that secreted compounds contained in the co-cultured supernatant contributed to the higher oxidative stress tolerance of S. cerevisiae. The potential key regulatory metabolite (i.e., hexadecanoic acid) with high content difference between co-cultured supernatant and the pure-cultured S. cerevisiae supernatant was discovered by GC-MS-based metabolomics strategy. And exogenous addition of hexadecanoic acid did suggest its contribution to higher oxidative stress tolerance of S. cerevisiae. Results presented here would contribute to the understanding of the microbial interactions and provide the foundation for improving the efficiency of co-fermentation performed by S. cerevisiae and E. coli.

Effects of Saccharomyces cerevisiae quorum sensing signal molecules on ethanol production in bioethanol fermentation process

In this study, the concentrations of Saccharomyces cerevisiae quorum sensing signal molecules (QSMs) were determined, not to mention the exploration of the effects of exogenous S. cerevisiae QSMs on the sole fermentation of S. cerevisiae and co-fermentation of S. cerevisiae and Lactobacillus plantarum. The results showed that the concentrations of three signal molecules (2-phenylethanol (2-PE), tyrosol and tryptophan) produced by S. cerevisiae increased with a higher bacteria density, which tends to become stable up to 118.02, 32.05 and 1.93 mg/L respectively when cultivating for 144 h. Among the three signaling molecules, only 2-PE promoted the ethanol production capacity of S. cerevisiae. The ethanol concentration of the sole fermentation of S. cerevisiae loaded with 120 mg/L 2-PE reached 3.2 g/L in 9 h, which was 58.7% higher than that of the group without 2-PE addition. Moreover, 2-PE reduced the negative impact of L. plantarum on S. cerevisiae. Within 12 h of the co-fermentation of L. plantarum and S. cerevisiae, the ethanol concentration in the co-fermentation group loaded with 2-PE reached 5.6 g/L, similar to that in the group fermenting with sole S. cerevisiae, and the yeast budding rate was also restored to 28.51%. qRT-PCR results of S. cerevisiae which was in sole fermentation with 2-PE addition for 9 h showed that the relative expression levels of ethanol dehydrogenase gene ADH1 in S. cerevisiae decreased by 25% and the relative expression levels of MLS1, CIT2, IDH1,CIT1 decreased by 26%, 30%, 22%,18%, respectively, meant that the glyoxylic and tricarboxylic acid cycles were greatly inhibited, which promotes the accumulation of ethanol. The results of this study provide basic data for using QSMs more than antibiotics in the the prevention of contamination during the industrialized bioethanol production.

Microbial Interaction between Lactiplantibacillus plantarum and Saccharomyces cerevisiae: Transcriptome Level Mechanism of Cell-Cell Antagonism

Lactiplantibacillus plantarum and Saccharomyces cerevisiae are frequently co-isolated in food, although playing different roles. This study aimed at investigating the microbial interaction between L. plantarum and S. cerevisiae, especially cell-cell direct interaction and their mechanism. Cell-cell and supernatant-cell coculture models were set up, with CFU counting, OD₆₀₀ measurement, optical and atomic force microscopy performed to examine the growth and morphology of L. plantarum and S. cerevisiae cells. In cell-cell coculture model, L. plantarum cells inhibited S. cerevisiae growth (inhibition rate ~80%) with its own growth pattern unaffected. Cell-cell aggregation happened during coculture with surface roughness changed and partial S. cerevisiae cell lysis. Mature (24 h) L. plantarum cell-free culture supernatant showed inhibition (35%-75%) on S. cerevisiae growth independent of pH level, while supernatant from L. plantarum-S. cerevisiae coculture showed relatively stronger inhibition. Upon transcriptomics analysis, hypothesis on the mechanism of microbial interaction between L. plantarum and S. cerevisiae was demonstrated. When L. plantarum cell density reached threshold at 24 h, all genes in lamBDCA quorum sensing (QS) system was upregulated to potentially increase adhesion capability, leading to the aggregation to S. cerevisiae cell. The downregulation of whole basic physiological activity from DNA to RNA to protein, cell cycle, meiosis, and mitogen-activated protein kinase (MAPK) signaling pathways, as well as growth maintenance essential genes ari1, skg6, and kex2/gas1 might induce the decreased growth and proliferation rate and partial death of S. cerevisiae cells in coculture. IMPORTANCE L. plantarum and S. cerevisiae are frequently co-isolated in food, although playing different roles. The co-existence of L. plantarum and S. cerevisiae could result in variable effects, raising economic benefits and safety concerns in food industry. Previous research has reported the microbial interaction between L. plantarum and S. cerevisiae mainly rely on the signaling through extracellular metabolites. However, cell-cell aggregation has been observed with mechanism remain unknown. In the current study, the microbial interaction between L. plantarum and S. cerevisiae was investigated with emphasis on cell-cell direct interaction and further in-depth transcriptome level study showed the key role of lamBDCA quorum sensing system in L. plantarum. The results yield from this study demonstrated the antagonistic effect between L. plantarum and S. cerevisiae.

Multi-Omics Reveals the Inhibition of Lactiplantibacillus plantarum CCFM8724 in Streptococcus mutans-Candida albicans Mixed-Species Biofilms

Lactiplantibacillus plantarum CCFM8724 is a probiotic with the potential to prevent dental caries in vitro and in vivo. To explore the effects of this probiotic at inhibiting Streptococcus mutans-Candida albicans mixed-species biofilm and preventing dental caries, multi-omics, including metabolomics and transcriptomics, was used to investigate the regulation of small-molecule metabolism during biofilm formation and the gene expression in the mixed-species biofilm. Metabolomic analysis revealed that some carbohydrates related to biofilm formation, such as sucrose, was detected at lower levels due to the treatment with the L. plantarum supernatant. Some sugar alcohols, such as xylitol and sorbitol, were detected at higher levels, which may have inhibited the growth of S. mutans. In transcriptomic analysis, the expression of the virulence genes of C. albicans, such as those that code agglutinin-like sequence (Als) proteins, was affected. In addition, metabolomics coupled with a Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and RNA-seq revealed that the L. plantarum supernatant had an active role in sugar metabolism during the formation of the S. mutans-C. albicans mixed-species biofilm, and the L. plantarum supernatant was also related to carbohydrate utilization, glucan biosynthesis, and mycelium formation. Hence, L. plantarum CCFM8724 decreased the mixed-species biofilm mass from the perspective of gene expression and metabolic reprogramming. Our results provide a rationale for evaluating L. plantarum CCFM8724 as a potential oral probiotic for inhibiting cariogenic pathogen biofilm formation and improving dental caries.

The Toxic Effects of Tetrachlorobisphenol A in Saccharomyces cerevisiae Cells via Metabolic Interference

Tetrachlorobisphenol A (TCBPA) is a common flame retardant detected in different environments. However, its toxic effects on animals and humans are not fully understood. Here, the differential intracellular metabolites and associated gene expression were used to clarify the metabolic interference of TCBPA in Saccharomyces cerevisiae, a simple eukaryotic model organism. The results indicated that TCBPA treatment promoted the glycolysis pathway but inhibited the tricarboxylic acid (TCA) cycle, energy metabolism and the hexose monophosphate pathway (HMP) pathway. Thus, the HMP pathway produced less reducing power, leading to the accumulation of reactive oxygen species (ROS) and aggravation of oxidative damage. Accordingly, the carbon flux was channelled into the accumulation of fatty acids, amino acids and glycerol instead of biomass production and energy metabolism. The accumulation of these metabolites might serve a protective function against TCBPA stress by maintaining the cell membrane integrity or providing a stable intracellular environment in S. cerevisiae. These results enhance our knowledge of the toxic effects of TCBPA on S. cerevisiae via metabolic interference and pave the way for clarification of the mechanisms underlying TCBPA toxicity in animals and humans.