Type 4 fimbriae (pili) are found in a wide variety of gram-negative bacteria and are composed of small structural subunits which share significant sequence homology among different species, especially at their amino-terminal ends. Previous studies demonstrating morphogenetic expression of Bacteroides nodosus fimbriae from cloned subunit genes in Pseudomonas aeruginosa suggested that there is a common mechanism for type 4 fimbriae assembly and that the structural subunits are interchangeable (J. S. Mattick et al., J. Bacteriol. 169:33-41, 1987). Here we have examined the expression of Moraxella bovis fimbrial subunits in P. aeruginosa. M. bovis subunits were assembled into extraceilular fimbriae in this host, in some cases as a homopolymer but in others as a mosaic with the indigenous subunit, indicating structural equivalence. This result contrasts with other studies in which recombinant P. aeruginosa expressing different subunits produced fimbriae composed almost exclusively of one subunit or the other (T. C. Elleman and J. E. Peterson, Mol. Microbiol. 1:377-380, 1987). Both observations can be explained by reversibility of subunit-subunit interactions at the site of assembly, with the forward equilibrium favoring chain extension between compatible subunits.Fimbriae, classified as type 4 by Ottow (20), are found in a wide range of bacterial pathogens, including Moraxella bovis, Neisseria gonorrhoeae, Neisseria meningitidis, Bacteroides nodosus, and Pseudomonas aeruginosa (7,14,18,19,22). The characteristics of type 4 fimbriae include a predominantly polar location on the cell, association with a phenomenon known as "twitching motility," and certain conserved features of the structural subunit which composes the fimbrial strand (7, 18). The structural subunits vary from about 145 to 160 amino acids long (approximately 16,000 molecular weight) between different genera, species, and serotypes, but all contain a highly homologous and hydrophobic amino-terminal region. In addition, most contain an unusual modified amino acid, N-methylphenylalanine, as the first residue in the mature protein, which is produced from a preprotein by cleavage of a short (six-to seven-amino-acid) positively charged leader sequence. Intergenera, interspecies, and interserotype variations occur primarily in the carboxy-terminal two-thirds of the protein (7, 18).The conserved amino-terminal region of the subunit is thought to contain important signals for the structure and assembly of the fimbrial strand. The high degree of sequence conservation would also suggest that these various type 4 fimbriate organisms use a common mechanism for fimbrial biosynthesis (18). This was supported by the demonstration of high-level morphogenetic expression of B. nodosus fimbriae from a cloned subunit gene (under appropriate promoter control) in P. aeruginosa (18) and the subsequent use of this material to vaccinate sheep against footrot (8).In this study we used a similar approach to demonstrate morphogenetic expression of M. bovis fimbriae from a cloned ...

Moraxella bovis, the causative agent of infectious bovine keratoconjunctivitis, exhibits several virulence factors, including pili, haemolysin, leukotoxin, and proteases. The pili are filamentous appendages which mediate bacterial adherence. Prior studies have shown that Q-piliated M. bovis Epp63 are more infectious and more pathogenic than I-piliated and non-piliated isogenic variants, suggesting that Q pili per se, or traits associated with Q-pilin expression, promote the early association of Q-piliated bacteria with bovine corneal tissue. In order to better evaluate the role of Q pili in M. bovis attachment, several M. bovis strains and a recombinant P. aeruginosa strain which elaborates M. bovis Q pili but not P. aeruginosa PAK pili, were evaluated using an in vitro corneal attachment assay. For each strain tested, piliated organisms attached better than non-piliated bacteria. M. bovis Epp63 Q-piliated bacteria adhered better than either the I-piliated or non-piliated isogenic variants. Finally, recombinant P. aeruginosa organisms elaborating M. bovis Q pili adhered better than the parent P. aeruginosa strain which did not produce M. bovis pili. These results indicate that the presence of pili, especially Q pili, enhances the attachment of bacteria to bovine cornea in vitro.

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