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Two linked genes for outer membrane proteins are absent in four non-disease strains of Haemophilus somnus
S P Cole1, D G Guiney, L B Corbeil
1Department of Pathology, University of California, San Diego 92103-8416.
Abstract:
Linked genes encoding two outer membrane proteins (p76 and a family of proteins, p120) of the bovine pathogen, Haemophilus somnus, were investigated. The p120 group was previously shown to have immunoglobulin-binding activity and to react with polyclonal antiserum specific for a 270 kDa antigen (p270) which also had immunoglobulin Fc-binding activity. By Western blotting we showed that the p76 antigen also reacted with this antiserum. The p270, p120, and p76 antigens were undetectable in four serum-sensitive isolates from asymptomatic carriers but were present in the two serum-resistant virulent strains tested. Genes for p120 and p76 were subcloned on non-overlapping pUC plasmids from a cosmid (pHS1) originally cloned from a serum-resistant strain. In Escherichia coli, plasmid pHS138 expressed p76, while the p120 antigens were produced by pHS140. Southern blots of DNA from the above six strains of H. somnus using probes derived from pHS1 subclones showed that a 13.4 kb sequence was missing from the four serum-sensitive strains, but not the two serum-resistant strains. This segment included most of the insert in pHS138 and all of the pHS140 insert. The data indicate that p76 and the p120 proteins are absent from serum-sensitive strains because the coding sequences are missing, raising the possibility of insertion of these genes into the chromosome of both serum-resistant strains, or deletion from the four serum-sensitive strains.
Insights
Outer membrane proteins p76 and p120 are crucial for Haemophilus somnus virulence. Serum-sensitive strains lack these proteins due to gene deletion, impacting bovine health.
Area of Science:
- Veterinary Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Haemophilus somnus is a significant bovine pathogen.
- Outer membrane proteins (p76, p120) and a 270 kDa antigen (p270) in H. somnus exhibit immunoglobulin-binding activity.
- These antigens are associated with serum resistance and virulence.
Purpose of the Study:
- To investigate the genes encoding outer membrane proteins p76 and p120 in Haemophilus somnus.
- To determine the presence or absence of these genes in virulent and avirulent strains.
- To elucidate the genetic basis of serum sensitivity/resistance in H. somnus.
Main Methods:
- Gene cloning and subcloning of p76 and p120 genes into pUC plasmids.
- Expression of cloned genes in Escherichia coli.
- Western blotting to detect antigen presence.
- Southern blotting to analyze DNA sequences in H. somnus strains.
Main Results:
- Antigens p76, p120, and p270 were detected in serum-resistant virulent H. somnus strains but absent in serum-sensitive avirulent strains.
- Genes for p76 and p120 were successfully cloned and expressed in E. coli.
- A 13.4 kb DNA sequence containing the p76 and p120 coding regions was present in serum-resistant strains and absent in serum-sensitive strains.
Conclusions:
- Serum sensitivity in H. somnus is linked to the absence of p76 and p120 outer membrane proteins.
- The absence of these proteins in sensitive strains is due to the deletion of their coding sequences.
- These findings suggest a potential role for gene deletion or insertion in the virulence and serum resistance of H. somnus.