Metabolomic Approaches to Study the Potential Inhibitory Effects of Plantaricin Q7 against Listeria monocytogenes Biofilm

Abstract

Listeria monocytogenes is a serious pathogen and can exacerbate harmful effects through the formation of biofilm. Inhibition of or reduction in L. monocytogenes biofilm is a promising strategy to control L. monocytogenes in the food industry. In our previous study, it was found that plantaricin Q7 produced by Lactiplantibacillus plantarum Q7 could inhibit and reduce L. monocytogenes biofilm, but the specific mechanism remains unclear. In this study, the inhibitive and reduced activity of plantaricin Q7 on L. monocytogenes biofilm was investigated by metabolomics. The results showed that plantaricin Q7 inhibited the synthesis of L. monocytogenes biofilm mainly through purine metabolism and glycerol phospholipid metabolism, and the key differential metabolites included acetylcholine and hypoxanthine with a decrease in abundance from 5.80 to 4.85. In addition, plantaricin Q7 reduced the formed L. monocytogenes biofilm by purine metabolism and arginine biosynthesis, and the main differential metabolites were N-acetylglutamate and D-ribose-1-phosphate with a decrease in abundance from 6.21 to 4.73. It was the first report that purine metabolism and amino acid metabolism were the common metabolic pathway for plantaricin Q7 to inhibit and reduce L. monocytogenes biofilm, which could be potential targets to control L. monocytogenes biofilm. A putative metabolic pathway for L. monocytogenes biofilm inhibition and reduction by plantaricin Q7 was proposed. These findings provided a novel strategy to control L. monocytogenes biofilm in food processing.

Keywords: Listeria monocytogenes biofilm; inhibition; metabolomics; plantaricin Q7; reduction.

Figure 1

PCA score plots and PLS-DA score plots. (A) PCA scores of samples in inhibition group and reduction group. (B) Volcano plot of inhibition group and reduction group. The points below the red dashed line indicate no change.

Figure 2

Differential metabolite classification in inhibition group and reduction group.

Figure 3

Enrichment analysis bubble diagrams of KEGG metabolic pathway in samples from inhibition group and reduction group.

Figure 4

Venn diagram of enrichment pathway. The yellow circle represents the Inhibition_TR vs. Inhibition_Control group, and the blue circle represents the Reduction_TR vs. Reduction_Control.

Figure 5

Purine metabolic pathway and major metabolites. (A) Purine metabolic pathway; (B) metabolites in purine metabolic pathway. Blue words indicate the metabolites with significant differences between the inhibition group and the reduction group, green words indicate the metabolites with significant differences only in the inhibition group, and red words indicate the metabolites with significant differences only in the reduction group. ↑ indicates up-regulation and ↓ indicates down-regulation. * p < 0.05, ** p < 0.01, *** p < 0.001, ns, not significant.

Figure 6

Effect of plantaricin Q7 on amino acid metabolism. (A) Inhibition_TR vs. Inhibition_Control group; (B) Reduction_TR vs. Reduction_Control group. ** p < 0.01, *** p < 0.001.

Figure 7

Glycerol phospholipid metabolic pathway and major metabolites. (A) Glycerol phospholipid metabolic pathway; (B) effect of plantaricin Q7 on metabolites of glycerol phospholipid metabolic pathway in the inhibition group. The black words in Figure 7A represent metabolites with no significant changes, while the green words represent metabolites with significant changes. Green ↑ indicates up-regulation and green ↓ indicates down-regulation. * p < 0.05, *** p < 0.001.

Figure 8

Arginine biosynthesis pathway and major metabolites. (A) Arginine biosynthesis pathway; (B) effect of plantaricin Q7 on metabolites of arginine biosynthesis pathway in the reduction group. Red indicates metabolites with significant differences. Red ↑ indicates up-regulation and red ↓ indicates down-regulation. * p < 0.05, ** p < 0.01, *** p < 0.001.

Figure 9

Metabolic pathways related to the inhibition and reduction in L. monocytogenes biofilm by plantaricin Q7. The red text boxes indicate up-regulation and the blue text boxes indicate down-regulation. The orange dashed circles represent the two metabolites with the largest difference in fold in the inhibition groups, and the green dashed circles represent the two metabolites with the largest difference in fold in the reduction groups. The remaining dashed lines indicate direct or indirect connections between metabolic pathways. The green background indicates purine metabolism, the gray background indicates arginine biosynthesis, the pink background indicates glycerol phospholipid metabolism, and the light orange background indicates plantaricin Q7 acting on the L. monocytogenes biofilm.