Related Experiment Videos
Complete nucleotide sequence and molecular characterization of ViaB region encoding Vi antigen in Salmonella typhi
Y Hashimoto1, N Li, H Yokoyama
1Department of Microbiology, Gifu University School of Medicine, Japan.
Abstract:
Plasmid pGBM124, which contains a 14-kb Salmonella typhi chromosomal DNA fragment capable of producing the Vi antigen in Escherichia coli HB101 and ViaB-deleted S. typhi GIFU 10007-3, was studied. We determined the complete nucleotide sequence of this fragment and found 11 open reading frames. Mutagenesis, subcloning, and complementation analysis showed that three genes (vipA, vipB, and vipC) are involved in biosynthesis of the Vi polysaccharide. The putative primary amino acid sequence suggests that both vipA and vipB encode the NAD- or NADP-dependent enzymes to synthesize the nucleotide sugar for the Vi polysaccharide. Five genes (vexA, vexB, vexC, vexD, and vexE) may be involved in translocation of the Vi polysaccharide. Proteins VexA, VexB, VexC, and VexD had moderate similarities to components of group II capsule transporters, and the VexC protein had a putative ATP-binding site. These data indicate that the transport system for the Vi polysaccharide belongs to the ATP-binding cassette transporters. By using the isogenic Vi+ and Vi- strains constructed in this study, we reconfirmed that the Vi antigen is necessary for the serum resistance of S. typhi.
Insights
Researchers identified genes responsible for Salmonella typhi Vi antigen biosynthesis and transport. These findings confirm the Vi antigen
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- The Vi antigen is a crucial virulence factor for Salmonella typhi, contributing to serum resistance.
- Understanding the genetic basis of Vi antigen production and transport is essential for developing effective typhoid fever interventions.
Purpose of the Study:
- To elucidate the genetic mechanisms underlying Vi polysaccharide biosynthesis and translocation in Salmonella typhi.
- To characterize the genes and proteins involved in Vi antigen production and transport.
Main Methods:
- Nucleotide sequencing of the 14-kb Salmonella typhi DNA fragment.
- Gene mutagenesis, subcloning, and complementation analysis.
- Bioinformatic analysis of open reading frames and protein sequences.
Main Results:
- Identified 11 open reading frames, with vipA, vipB, and vipC genes essential for Vi polysaccharide biosynthesis.
- Discovered five genes (vexA-E) likely involved in Vi polysaccharide translocation, suggesting an ATP-binding cassette transporter system.
- Confirmed the necessity of the Vi antigen for Salmonella typhi serum resistance.
Conclusions:
- The study delineates the genetic machinery for Vi antigen production and transport in Salmonella typhi.
- The identified genes provide targets for novel therapeutic strategies against typhoid fever.
- The Vi antigen plays a critical role in Salmonella typhi's survival against host immune defenses.