Table 1. Bacterial strains and plasmids used in this study.

Strains/plasmid	Characteristics/Functions	Source/Reference
Bacterial strains
E. coli DH5a	Cloning vehicle: clone the upstream and downstream flanking regions of ssnA	Invitrogen
E. coli BL21(DE3)	For expressing the recombinant plasmids	Invitrogen
S. suis GD01	Serotype 2, clinical isolated virulent strain	Laboratory collection
ΔssnA	The deletion mutant of ssnA with background of GD01	This study
C-ΔssnA	Complemented strain of ssnA	This study
Plasmids
pMD19-T	Cloning vector; AmpR	TaKaRa
pSET4s	E. coli–S. suis shuttle vector thermosensitive suicide; SpcR	Takamatsu et al., 2001
pSET4sΔssnA	A recombinant vector with the background of pSET4s, designed to knockout ssnA; SpcR	This study
pAT18	A plasmid carrying an erythromycin resistance rRNA methylase (Erm) gene expression cassette	Trieu-Cuot et al., 1991
pAT18-ssnA	A recombinant vector with the background of pAT18, designed to complementation ssnA; ErmR	This study