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Aeromonas spp. possess at least two distinct type IV pilus families
T C Barnett1, S M Kirov, M S Strom
1Division of Pathology, University of Tasmania, GPO 252-29, Hobart, Tasmania, 7001, Australia.
Abstract:
Type IV pili have been purified from strains of most of the Aeromonas species associated with gastroenteritis (A. veronii biovar sobria, A. hydrophila, A. trota and A. caviae). They appear to be a related family (molecular mass of pilin 19 to 23 kDa) with a tendency to bundle-formation. Hence, we have designated them 'bundle-forming pili' (Bfp). A type IV pilus biogenesis gene cluster (tapABCD) recently cloned from a strain of A. hydrophila, however, encoded a 17 kDa pilin which differed significantly in its N-terminal amino acid sequence from the Bfp pilins. This paper describes the cloning of part (tapA and approximately 20% of tapB) of a homologous pilin gene cluster from a Bfp-positive strain of A. veronii biovar sobria, and presents evidence that the entire pilin gene cluster (tapABCD) is present in this strain. The predicted N-terminal amino acid sequence of the pilin encoded by the A. veronii biovar sobria tapA differed markedly from the corresponding sequence of its Bfp pilin, and those of the Bfp purified from other Aeromonas strains and species. Probing with tapA and tapD genes showed that these Bfp-positive Aeromonas strains also possessed the Tap gene cluster. TapA proteins of A. veronii biovar sobria and A. hydrophila shared 53% identity and 63% homology. We conclude that Aeromonas species are potentially able to express at least two distinct families of type IV pili (Bfp and Tap).
Insights
Aeromonas species possess at least two distinct types of type IV pili, bundle-forming pili (Bfp) and Tap pili. This study identifies and characterizes these pili, crucial for understanding Aeromonas pathogenesis.
Area of Science:
- Microbiology
- Molecular Biology
- Bacterial Pathogenesis
Background:
- Type IV pili are surface appendages found in many bacteria, playing roles in motility, adhesion, and biofilm formation.
- Aeromonas species, particularly those causing gastroenteritis, possess pili that contribute to their virulence.
- Previous work identified bundle-forming pili (Bfp) in Aeromonas, but a distinct type IV pilus biogenesis gene cluster (tapABCD) was also found in A. hydrophila, encoding a different pilin.
Purpose of the Study:
- To investigate the presence and characteristics of pilin gene clusters in Aeromonas species associated with gastroenteritis.
- To compare the pilins encoded by different gene clusters and determine if Aeromonas expresses multiple pilus types.
Main Methods:
- Purification of type IV pili from various Aeromonas strains.
- Cloning of pilin gene clusters, specifically tapA and part of tapB, from A. veronii biovar sobria.
- N-terminal amino acid sequencing of pilins.
- Gene probing using tapA and tapD to detect the presence of the Tap gene cluster.
- Sequence analysis to determine protein identity and homology.
Main Results:
- Aeromonas species associated with gastroenteritis possess bundle-forming pili (Bfp) with pilin molecular masses of 19-23 kDa.
- A homologous pilin gene cluster (tapABCD) was identified in A. veronii biovar sobria, encoding a 17 kDa pilin distinct from Bfp pilins.
- The TapA proteins from A. veronii biovar sobria and A. hydrophila showed 53% identity and 63% homology.
- Gene probing confirmed the presence of the Tap gene cluster in Bfp-positive Aeromonas strains.
Conclusions:
- Aeromonas species can express at least two distinct families of type IV pili: bundle-forming pili (Bfp) and Tap pili.
- The presence of multiple pilus types suggests a complex role in Aeromonas pathogenesis and adaptation.