A 990-bp PCR fragment containing the 477-bp upstream of the ATG start codon and the 513-bp downstream of the TAA stop codon of ompP2 gene was amplified using overlap PCR with primers (P1 and P4) and subsequently cloned into plasmid pK18mobsacB to create pZB1. Both DNA fragments (upstream and downstream) contained the 9-bp core DNA uptake signal sequence (USS) of 5′-ACCGAACTC (Bigas et al., 2005). Next, an 800-bp gentamicin resistance cassette was amplified from a p34s-Gm plasmid with primers (P5 and P6). Both the pZB1 and the gentamicin resistance cassette were digested with BamHI and SalI and then ligated together to form plasmid pZB2.

A pZB3 plasmid PF-02341066 datasheet contained the entire heptosyltransferase (hep) II gene plus 517-bp upstream of the ATG start codon and 433-bp downstream of the TAA stop codon, and the gentamicin resistance cassette ligated between the hepII gene and the downstream sequence. To obtain plasmid pZB4, a mutation cassette of the OmpP2 gene was amplified from the pZB1 plasmid using primers (P11 and P12) containing AZD3965 a novel putative USS of 5′-ACCGCTTGT. Next, this PCR product was cloned into pK18mobsacB to make pZB4. A 2.32-kb PCR fragment was amplified using overlap PCR with primers (P13 and P16), which contained the complete open reading frame (ORF) of ompP2 gene and the kanamycin resistance cassette. Both

the fragment and the pZB3 plasmid were excised with BamHI and SalI and then ligated together to form plasmid pZB5. All plasmids were mobilized into E. coli DH5α by CaCl2-mediated transformation. A natural transformation assay was performed using the method of Bigas et al. (2005) with some modifications. Recipient bacteria were cultured overnight at 37 °C and resuspended in TSB supplemented with serum and NAD at 5 × 1010 CFU mL−1. A 20-μL aliquot

of the suspension was spotted onto a TSA plate supplemented with serum and Carbohydrate NAD and spread onto a small area. Next, 1 μg of donor DNA plasmid resuspended in TE buffer was added, mixed and incubated for 5 h at 37 °C. Bacterial cells were scraped up and plated on the selective medium and incubated at 37 °C for 2–3 days. Additionally, TE buffer was added to a bacterial spot, instead of donor DNA, as a negative control. To characterize the outer membrane protein (OMP) profiles of the wild-type and mutant strains, OMPs were extracted from H. parasuis according to a previously described method with some modifications (Zhou et al., 2009). Briefly, H. parasuis cultures were harvested by centrifugation for 10 min at 4500 g. The pellet was resuspended in 10 mM HEPES buffer (pH 7.4), and the suspension was subjected to sonication. Cellular debris was removed by centrifugation (10 000 g, 10 min, 4 °C). The supernatant was then removed and centrifuged at 200 000 g for 45 min at 4 °C. The supernatant was discarded, and the pellets were resuspended and washed in 10 mM HEPES buffer (pH 7.