This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Boekema, B. K. H. L. Articles by Smith, H. E. Search for Related Content PubMed PubMed Citation Articles by Boekema, B. K. H. L. Articles by Smith, H. E.

Host Cell Contact-Induced Transcription of the Type IV Fimbria Gene Cluster of Actinobacillus pleuropneumoniae

Division of Infectious Diseases and Food Chain Quality, Institute for Animal Science and Health, ID-Lelystad, 8200 AB Lelystad,¹ Department of Infectious Diseases and Immunology, Utrecht University, 3508 TD Utrecht, The Netherlands²

Received 13 May 2003/ Returned for modification 29 July 2003/ Accepted 5 November 2003

Type IV pili (Tfp) of gram-negative species share many characteristics, including a common architecture and conserved biogenesis pathway. Much less is known about the regulation of Tfp expression in response to changing environmental conditions. We investigated the diversity of Tfp regulatory systems by searching for the molecular basis of the reported variable expression of the Tfp gene cluster of the pathogen Actinobacillus pleuropneumoniae. Despite the presence of an intact Tfp gene cluster consisting of four genes, apfABCD, no Tfp were formed under standard growth conditions. Sequence analysis of the predicted major subunit protein ApfA showed an atypical alanine residue at position -1 from the prepilin peptidase cleavage site in 42 strains. This alanine deviates from the consensus glycine at this position in Tfp from other species. Yet, cloning of the apfABCD genes under a constitutive promoter in A. pleuropneumoniae resulted in pilin and Tfp assembly. Tfp promoter-luxAB reporter gene fusions demonstrated that the Tfp promoter was intact but tightly regulated. Promoter activity varied with bacterial growth phase and was detected only when bacteria were grown in chemically defined medium. Infection experiments with cultured epithelial cells demonstrated that Tfp promoter activity was upregulated upon adherence of the pathogen to primary cultures of lung epithelial cells. Nonadherent bacteria in the culture supernatant exhibited virtually no promoter activity. A similar upregulation of Tfp promoter activity was observed in vivo during experimental infection of pigs. The host cell contact-induced and in vivo-upregulated Tfp promoter activity in A. pleuropneumoniae adds a new dimension to the diversity of Tfp regulation.

Editor: V. J. DiRita

This article has been cited by other articles:

• Bakaletz, L. O., Baker, B. D., Jurcisek, J. A., Harrison, A., Novotny, L. A., Bookwalter, J. E., Mungur, R., Munson, R. S. Jr. (2005). Demonstration of Type IV Pilus Expression and a Twitching Phenotype by Haemophilus influenzae. Infect. Immun. 73: 1635-1643 [Abstract] [Full Text]  
• Jacobsen, I., Hennig-Pauka, I., Baltes, N., Trost, M., Gerlach, G.-F. (2005). Enzymes Involved in Anaerobic Respiration Appear To Play a Role in Actinobacillus pleuropneumoniae Virulence. Infect. Immun. 73: 226-234 [Abstract] [Full Text]