Exogenous L-Cysteine and Its Transport Through CtaP Play a Role in Biofilm Formation, Swimming Motility, and Swarming Motility of Listeria monocytogenes

Abstract

Listeria monocytogenes is of a significant concern for the food industry, largely due to its ability to form biofilms. Flagellar motility and environmental factors are crucial for biofilm formation. Cysteine is an important compound affecting the behavior of this bacterium; therefore, we investigated its role in growth, biofilm formation and motility of L. monocytogenes 10403S through a mutant in cysteine uptake (ΔctaP). Basal defined media (DM) and L-cysteine-supplemented DM were used. Biofilm formation was promoted by L-cysteine supplementation in both wild type (WT) and ΔctaP. Lower biofilm formation of ΔctaP compared to WT indicates the significance of the cysteine transporter and cysteine uptake. A negative correlation was found between growth and biofilm formation, especially in the presence of high L-cysteine concentrations. Motility experiments showed that as the L-cysteine concentration increased, the swarming motility of WT decreased. Furthermore, swimming motility of WT was enhanced with L-cysteine supplementation, while the swimming motility of ΔctaP remained unaffected. To evaluate the role of cysteine and CtaP in biofilm formation and motility, transcriptome analysis, comparing WT and ΔctaP in basal and L-cysteine-supplemented (1.57 and 3.67 mM) DM, was conducted at 37 °C. The investigation of biofilm-related genes explained the role of ctaP and revealed induced expression of flagella and chemotaxis genes by L-cysteine.

Keywords: Listeria monocytogenes; bacterial adhesion; ctaP; cysteine transporter; environmental sensing; flagellar motility; quorum sensing.

Figure 1

Biofilm formation (bars) and growth (lines) of WT (black bars and round markers) and ΔctaP (white bars and triangle markers) in DMs supplemented with different L-cysteine concentrations were measured after 24 h of growth at 30 °C (A) and 37 °C (B). Bars and lines are calculated from three identical biological replicates and error bars represent the standard deviation. Different upper cases show a significant difference between WT strains in DMs (p < 0.05). Different lower cases show a significant difference between ΔctaP strains in DMs (p < 0.05). Asterisks indicate a significant difference between WT and ΔctaP strains in the same media (p < 0.05).

Figure 2

Swarming motility of WT (black bars) and ΔctaP (white bars) cells in DM plates supplemented with different L-cysteine concentrations after 3 days of incubation at 20 °C (A), 25 °C (B), 30 °C (C), and 37 °C (D). Bars calculated from three biological replicates and error bars represent the standard deviation. Different upper cases show a significant difference between WT strains in DMs (p < 0.05). Different lower cases show a significant difference between ΔctaP strains in DMs (p < 0.05). Asterisks indicate a significant difference between WT and ΔctaP strains in the same media (p < 0.05).

Figure 3

Swimming motility of WT (black bars) and ΔctaP (white bars) cells in DM plates supplemented with different L-cysteine concentrations after 3 days of incubation at 20 °C (A), 25 °C (B), 30 °C (C), and 37 °C (D). Bars calculated from three biological replicates and error bars represent standard deviation. Different upper cases show a significant difference between WT strains in DMs (p < 0.05). Different lower cases show a significant difference between ΔctaP strains in DMs (p < 0.05). Asterisks indicate a significant difference between WT and ΔctaP strains in the same media (p < 0.05).