An Aeromonas salmonicida type IV pilin is required for virulence in rainbow trout Oncorhynchus mykiss

Abstract

Aeromonas salmonicida expresses a large number of proven and suspected virulence factors including bacterial surface proteins, extracellular degradative enzymes, and toxins. We report the isolation and characterization of a 4-gene cluster, tapABCD, from virulent A. salmonicida A450 that encodes proteins homologous to components required for type IV pilus biogenesis. One gene, tapA, encodes a protein with high homology to type IV pilus subunit proteins from many Gramnegative bacterial pathogens, including Aeromonas hydrophila, Pseudomonas aeruginosa, and Vibrio vulnificus. A survey of A. salmonicida isolates from a variety of sources shows that the tapA gene is as ubiquitous in this species as it is in other members of the Aeromonads. Immunoblotting experiments demonstrate that it is expressed in vitro and is antigenically conserved among the A. salmonicida strains tested. A mutant A. salmonicida strain defective in expression of TapA was constructed by allelic exchange and found to be slightly less pathogenic for juvenile Oncorhynchus mykiss (rainbow trout) than wild type when delivered by intraperitoneal injection. In addition, fish initially challenged with a high dose of wild type were slightly more resistant to rechallenge with wild type than those initially challenged with the tapA mutant strain, suggesting that presence of TapA contributes to immunity. Two of the other three genes identified, tapB and tapC, encode proteins with homology to factors known to be required for type IV pilus assembly in P. aeruginosa, but in an as yet unidentified manner. TapB is a member of the ABC-transporter family of proteins that contain characteristic nucleotide-binding regions, and which may provide energy for type IV pilus assembly through the hydrolysis of ATP. TapC homologs are integral cytoplasmic membrane proteins that may play a role in pilus anchoring or initiation of assembly. The fourth gene, tapD, encodes a product that shares homology with a family of proteins with a known biochemical function, namely, the type IV prepilin leader peptidases. These bifunctional enzymes proteolytically cleave the leader peptide from the pilin precursor (prepilin) and then N-methylate the newly exposed N-terminal amino acid prior to assembly of the subunits into the pilus structure. We demonstrate that A. salmonicida TapD is able to restore type IV pilus assembly and type II secretion in a P. aeruginosa strain carrying a mutation in its type IV peptidase gene, suggesting that it plays the same role in A. salmonicida.KEY WORDS: Virulence · Type IV pilin · Type II protein secretion Resale or republication not permitted without written consent of the publisherDis Aquat Org 51: [13][14][15][16][17][18][19][20][21][22][23][24][25] 2002 A. salmonicida. These include proteases (Sakai 1985), hemolysins and cytolysins (Hirono & Aoki 1993, Ellis 1997, a phospholipase (Buckley et al. 1982), a paracrystalline surface array protein (S-layer) (Trust 1993), and an extracellular polysaccharide capsule (Merino et al. 1996).In recent s...

Are type IV pili involved in <i>Vibrio anguillarum</i> virulence towards sea bass (<i>Dicentrarchus labrax</i> L.) larvae?

“…It has for example been reported that the Aeromonas salmonicida PilA homologue, TapA, was required for virulence in rainbow trout (Oncorhynchus mykiss (Walbaum)) and Atlantic salmon (Salmo salar L.) [11,14]. In addition, the pilA-encoded type IV pilus of V. vulnificus contributed significantly to the persistence in Crassostrea virginica oysters [13].…”

“…Focusing on the major pilin, PilA, considerable homology to the type IV pilin precursor proteins of many other bacteria was observed [11,26,28,35,36]. Typically, the N-terminal region of the premature PilA of V. anguillarum VIB15 is dominated by a short, hydrophilic leader peptide and shows the presence of the conserved consensus cleavage site with the GFTLIE amino acid motif, which is identical in PilA of several other Vibrio species such as V. cholerae [26].…”

“…In addition to the role as adherence factors to living and nonliving surfaces, these pili have an important function in other bacterial processes as well, including flagellum-independent twitching motility, DNA uptake and exchange, biofilm formation, and secretion of extracellular proteins [8,9]. Furthermore, type IV pili have been identified as important virulence factors in several human, plant and animal pathogens, including several fish pathogens [8,[10][11][12][13][14]. Type IV pili possibly contribute to the pathogen's virulence by their roles in adhesion, immune escape, surface motility, microcolony formation, and complement inhibition [8].…”

An Overview of Virulence-Associated Factors of Gram-Negative Fish Pathogenic Bacteria

“…In vivo experiments in rainbow trout (Oncorhynchus mykiss) showed that the Tap pilus contributes moderately to virulence. A tapA mutant constructed by allelic exchange was found to be slightly less pathogenic than wild type when delivered by intraperitoneal injection (Masada et al, 2002). Boyd et al (2008) showed that the Tap pilus also made a moderate contribution to virulence in Atlantic salmon (Salmo salar), while the Flp pilus made little or no contribution.…”

Effect of Different Culture Conditions on the (Twitching) Displacement of Photobacterium Damselae subsp. Piscicida

“…It is located on the surface of many Gram-negative and Gram-positive bacteria, at one or both poles [18][19][20]. And also, it is involved in surface adhesion and colonization [21][22][23], tropism determination [24], biofilm formation [23], genetic material uptake [21] and virulence of bacteria [25][26][27]. Fimbriae expression is controlled by transcriptional and post-transcriptional [28] and is influenced by several factors: bacterial growth rate [29], culture medium composition [30,31], temperature [32], pH and osmolarity [33].…”