Complete Genome Sequence And Comparative Analysis Of Swine Pathogen Salmonella Choleraesuis SC-B67

We reported the whole genome sequence of Salmonella enterica serovar Choleraesuis SC-B67,which is one of more than 2,500 serotypes of Salmonella genus and performed comparative analysis with the genomics sequences of S.Typhi,S. Typhimurium and S.Paratyphi A.S.Choleraesuis has a narrow host range and is mostly adapted to swine and occasionally infect human.Genome-wide Comparison of these bacteria and their plasmids has revealed the similarities and differences in terms of conservation,virulence,mobile elements,metabolic competence and regulatory mechanisms.The genome of S.Choleraesuis SC-B67 is composing of one chromosome which is 4,755,700 bp in length and two plasmid,pSC138 and pSCV50.S.Choleraesuis SC-B67 contains 4447 ORFs and 151 pseudogenes while kept intact in S. Typhimurium and S.Typhi.Among the three Salmonella genomes,SC-B67 has the highest percentage of pseudogenes which is involved in the mobility and bacterial chemotaxis signal-transduction metabolize pathway.We speculate that the mutations in these genes my increase smooth swimming of the SC-B67,hence potentially increase the possibility of the effective interaction with and invasion of the host cells,pSC138 is 138,742 bp in length,encoded 176 ORFs.Plasmid pSC138 has eight insert sequences and seven transposons.These mobility elements enhance the flexibility of the plasmid;promote the exchange of the genetic elements with other bacteria and plasmids.A lot of antimicrobial resistant are combine with the mobile element,such as dhfr,sulâ… ,sulâ…¡,catâ… ,camlA,bla,strA,aad2,tetR,aph,sat,mef mer,ebr and qac. pSC138 is resistant to all antimicrobial agents commonly used to treat patients with invasive salmonellosis,including ampicillin,chloramphenicol, trimethoprim-sulfamethoxazole,ciprofloxacin,ceftriaxone and fluoroquinolone.These resistant genes which can successfully enhance the survival of the Salmonella in different host niche were acquired through the transduction of the insert sequences. The other plasmid is pSCV50 which is 49,588bp in length and encodes 52 ORFs. Comparative analysis of two 50-kb virulence plasmids of S.Choleraesuis SC-B67 (pSCV50) and RF-1(pKDSC50) were also carried out.The two plasmids share over 99%sequence identity.Ninety-two nucleotide variations at 42 sites were detected between the two plasmids.Two regions in pSCV50 appeared to be more susceptible to changes:one is the non-virulence associated transfer region and the other is a function-unknown region.The results indicate that virulence-related genes on the 50 kb plasmid are under negative selection,suggesting that they play important roles in the expression of virulence during the process of infection,while other genes in this plasmid tend to evolve neutrally.We also sequence another plasmid pOU7519 of the Salmonella strain OU7519. pOU7519 is a virulence and antimicrobial plasmid which is 127,212 bp encodes 146 ORFs.We found that this plasmid was composed of pSCV50 and part of the pSC138. The sequence 2,015 - 49,558 bp is 99%homologue to the pSCV50 while the rest sequence is 99%identity to the pSC138,but 53,133 bp of the pSC138(58,956 -112,089 ) has lost.