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A gonococcal porA pseudogene: implications for understanding the evolution and pathogenicity of Neisseria gonorrhoeae
1Division of Bacteriology, National Institute for Biological Standards and Control, Blanche Lane, South Mimms, Potters Bar, Herts EN6 3QG, UK.
Abstract:
Members of the genus Neisseria, including the human pathogens Neisseria meningitidis and Neisseria gonorrhoeae, express at least one member of a family of related porins. N. meningitidis is the only species known to express a second porin, the meningococcal serosubtyping antigen PorA, the most divergent member of this family. Unexpectedly, a porA gene was identified in the gonococcal genome. Both the gonococcal and meningococcal porA loci were adjacent to a homologue of the Escherichia coli greA gene, although the IS1106 element downstream of porA in some meningococci was absent in the gonococcus. Almost identical porA loci were present in four unrelated gonococcal isolates and clinical specimens from patients with gonorrhoea. Lack of PorA expression in the gonococcus resulted from mutations in the promoter region, which prevented transcription, and frameshift mutations in the coding region of the porA gene. Hybridization and amplification experiments, showing the absence of a porA gene in seven other Neisseria species, suggested that porA was acquired by a common ancestor of the gonococcus and meningococcus but inactivated in the gonococcus on speciation. This implies that, while advantageous during colonization of the upper respiratory tract, this protein has no function in, or hinders, colonization of the urogenital tract.
Insights
The porA gene, typically found in Neisseria meningitidis, was unexpectedly present but inactivated in Neisseria gonorrhoeae. This suggests PorA was lost during gonococcal evolution, impacting its colonization abilities.
Area of Science:
- Microbiology
- Genomics
- Bacterial Pathogenesis
Background:
- Neisseria species, including pathogens like Neisseria meningitidis and Neisseria gonorrhoeae, utilize porins for cellular functions.
- Neisseria meningitidis uniquely expresses the PorA protein, a divergent porin family member.
Purpose of the Study:
- To investigate the presence and function of the porA gene in Neisseria gonorrhoeae.
- To understand the evolutionary implications of porA gene acquisition and inactivation in Neisseria species.
Main Methods:
- Comparative genomics analysis of Neisseria species.
- PCR and hybridization experiments to detect the porA gene.
- Sequence analysis of gonococcal and meningococcal porA loci.
Main Results:
- The porA gene was identified in the Neisseria gonorrhoeae genome, adjacent to a greA homolog.
- Mutations in the promoter and coding regions of the porA gene prevent its expression in gonococci.
- The porA gene is absent in seven other Neisseria species, indicating inactivation post-speciation.
Conclusions:
- The porA gene was likely acquired by a common ancestor of gonococci and meningococci but subsequently inactivated in the gonococcal lineage.
- PorA expression may be beneficial for upper respiratory tract colonization but detrimental or non-functional for urogenital tract colonization by Neisseria gonorrhoeae.