Table 1 Bacterial strains and plasmids used in this study

Strains

 Χ232

E. coli Δasd strain used for cloning of genes into asd⁺ plasmid

[28]

 BL21(DE3)pLysS

F⁻, ompT, hsdS_B (r ⁻_B , m ⁻_B ), dcm, gal, λ (DE3), pLysS, Cm^r

Promega, USA

 JOL967

∆lon, ∆cpxR and ∆asd mutant of SG

[28]

 JOL916

∆lon and ∆cpxR mutant of SG

[28]

 JOL2068

JOL967 with pJHL65 plasmid

This study

 JOL2077

JOL967 with pJHL65-S1 plasmid

This study

 JOL1992

BL21(DE3)pLysS with pET28a-S1 plasmid

This study

Plasmids

 pJHL65

An asd⁺ vector, pBR ori, β-lactamase signal sequence-based periplasmic secretion plasmid, 6xHis, high copy number

 pJHL65-S1

pJHL65 carrying IBV S1 gene sequence

This study

 pET28a (+)

IPTG-inducible expression vector; Kan^r

Novagen, USA

 pET28a-S1

pET28a plasmid carrying S1 gene

This study