Tylosin Inhibits Streptococcus suis Biofilm Formation by Interacting With the O-acetylserine (thiol)-lyase B CysM

Abstract

Streptococcus suis (S. suis) can decrease its virulence or modify local conditions through biofilm formation, which promotes infection persistence in vivo. Biofilm formation is an important cause of chronic drug-resistant S. suis infection. The aim of this study was to evaluate whether tylosin effectively inhibits S. suis biofilm formation by interacting with O-acetylserine (thiol)-lyase B (CysM), a key enzymatic regulator of cysteine synthesis. Biofilm formation of the mutant (ΔcysM) strain was significantly lower compared to the wild-type ATCC 700794 strain. Tylosin inhibited cysM gene expression, decreased extracellular matrix contents, and reduced cysteine, homocysteine, and S-adenosylmethionine levels, indicating its potential value as an effective inhibitor of S. suis biofilm formation. Furthermore, using biolayer interferometry technology and fourier-transform infrared spectroscopy, we found that tylosin and CysM could be combined directly. Overall, these results provide evidence that tylosin inhibits S. suis biofilm formation by interacting with CysM.

Keywords: O-acetylserine (thiol)-lyase B (CysM); Streptococcus suis; biofilms; inhibition; tylosin.

Figure 1

Effects of tylosin on growth curves of Streptococcus suis. *P < 0.05 indicates a significant difference between the wild-type strain ATCC 700794 and the mutant (ΔcysM) strain at 24 h.

Figure 2

(A) Biofilm formation of the wild-type ATCC 700794 strain, the mutant (ΔcysM) strain and the complementary (CΔcysM) strain treated with tylosin or not. (B) Biofilm formation of the mutant (ΔcysM) strain treated with cysteine (100 μM and 500 μM) (*P < 0.05 and **P < 0.01 indicate significant difference).

Figure 3

Effect of tylosin on the biofilm morphology of the wild type strain ATCC 700794, the mutant (ΔcysM) strain and the complementary (CΔcysM) strain (Group descriptions are marked below each picture).

Figure 4

Effect of tylosin on the extracellular matrix of the wild-type ATCC 700794 strain, the mutant (ΔcysM) strain and the complementary (CΔcysM) strain treated or not treated with tylosin. (A) Effect of tylosin on the extracellular polysaccharide content; (B) effect of tylosin on extracellular DNA content; (C) effect of tylosin on extracellular protein content (**P < 0.01 indicate significant difference).

Figure 5

Regulatory effects of tylosin on cysteine metabolism pathway genes. Effect of 1/4 of MIC of tylosin on mRNA expression of the cysteine metabolism pathway genes in the wild-type ATCC 700794 strain (*P < 0.05 and **P < 0.01 indicate significant difference).

Figure 6

Regulation by tylosin of related metabolites in the cysteine synthesis pathway. (A) Effects of tylosin on cysteine content; (B) effects of tylosin on homocysteine content; (C) effect of tylosin on S-adenosylmethionine content (*P < 0.05 and **P < 0.01 indicate significant difference).

Figure 7

Purification and SDS-PAGE of CysM protein. (A) Ni column-purified protein absorption curve; (B) SDS-PAGE of CysM protein lane 1: Protein Maker; 2: CysM protein before induction; 3: CysM protein supernatant after induction; 4: CysM protein precipitate after induction; and 5: Purified mature CysM protein.

Figure 8

Detection of direct interaction between CysM and tylosin. (A) Binding dissociation curve of tylosin and CysM; (B) FT-IR analysis of combination between tylosin and CysM.