TABLE 1.

Bacterial strains or plasmid.

Plasmids	Characteristic(s) a	Reference or source
pET28a	Overexpression vector	Saved in our laboratory
pMD18-T	Cloning vector	Purchased from TaKaRa
pKD46	bla (Ap r), a helper plasmid for expression of Redλ recombinase	Donated by Guoqiang Zhu
pKD3	Template plasmid for a chloramphenicol resistance gene	Donated by Guoqiang Zhu
pKD4	bla (Ap r), a plasmid carrying FRT-flanked adjacent kan (Km r) gene	Donated by Guoqiang Zhu
pCP20	bla (Ap r) cat (Cm r), a plasmid for expression of FLP recombinase	Donated by Guoqiang Zhu
Bacterial strains
E. coli K-12	Wild type	Haerbin Veterinary Research Institute
E. coli DH5α E. coli BL21	Δ(argF-lac169)80 dlacZ58(M15)glnV44(AS)– rfbD1gyrA96 recA1 F– ompT gal dcm lon hsdSB(rB–mB–) λDE3	Purchased from Takara Saved in our laboratory
E. coli/pET28a	pET expression vector	This work
E. coli/pET28a-ybhF	pET28a-ybhF, Kanr	This work
E. coliΔybhF E. coliΔybhS E. coliΔybhR	E. coliΔybhF:Cl r E. coliΔybhS:Cl r E. coliΔybhR:Cl r	This work This work This work
E. coliΔacrB	E. coli ΔacrB: Ap r	This work
E. coliΔacrBΔybhF	E. coli ΔacrBΔybhF:Cl r	This work