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Infection and Immunity, October 2001, p. 6495-6502, Vol. 69, No. 10
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.10.6495-6502.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Intracellular Induction of the Bartonella henselae virB Operon by Human Endothelial Cells

Michael Schmiederer,1 Rodney Arcenas,1,2 Raymond Widen,1,2 Nikola Valkov,3 and Burt Anderson1,*

Department of Medical Microbiology and Immunology, College of Medicine, University of South Florida,1 and H. Lee Moffitt Cancer Center,3 Tampa, Florida 33612, and Department of Clinical Immunology, Tampa General Hospital, Tampa, Florida 336062

Received 24 April 2001/Returned for modification 12 June 2001/Accepted 9 July 2001

One of the more recently identified bacterial exportation systems is the type IV secretion mechanism, which is characterized by a multiprotein complex that spans the inner and outer bacterial membranes and contains a pilin component. The most thoroughly studied type IV secretion system is encoded by the virB operon of Agrobacterium tumefaciens. In Bartonella henselae, 8 of the 10 virB operon genes share extensive homology and arrangement with the virB operon of A. tumefaciens. Sequencing of the region upstream of the B. henselae virB2 gene revealed a region with sequence homology to the vir box of A. tumefaciens. This possible promoter region was cloned upstream of the green fluorescent protein reporter gene in the promoterless vector pANT3 and used to transform B. henselae. Minimal reporter gene expression was seen in the transformed bacteria cultivated in the absence of host cells, but expression was strongly induced in intracellular bacteria cultivated with human microvascular endothelial cells. Deletion of an 87-bp fragment, which contained the putative vir box from the 5' end of the promoter region, diminished intracellular induction of the reporter gene. Host cell induction of the 17-kDa antigen gene, which replaces virB5 in B. henselae, was also demonstrated at the protein level using specific antiserum. Thus, expression of the virB genes of B. henselae is induced in bacteria, which have invaded host cells, through a mechanism that may be similar to the environment-sensing mechanism found in the virB operon of A. tumefaciens.

* Corresponding author. Mailing address: Department of Medical Microbiology and Immunology, College of Medicine MDC 10, University of South Florida, 12901 Bruce B. Downs Blvd., Tampa, FL 33612. Phone: (813) 974-2608. Fax: (813) 974-4151. E-mail: banderso{at}hsc.usf.edu.

Infection and Immunity, October 2001, p. 6495-6502, Vol. 69, No. 10
0019-9567/01/$04.00+0   DOI: 10.1128/IAI.69.10.6495-6502.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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