Research in my laboratory is focused on the virulence factors and pathogenic mechanisms of the gram-negative bacterium Burkholderia cenocepacia. B. cenocepacia has emerged as an important opptunistic pathogen of the lower respiratory tract, affecting immunocompr mised individuals and particularly cystic fibrosis (CF) patients.
Mohr Lab Projects:
Analysis of a two-component signal transduction system controlling cable pilus biogenesis in B. cenocepacia.
Cable pili are unique peritrichous adherence organelles expressed by certain strains of B. cenocepacia that have been shown to mediate binding to both cellular and acellular receptors and likely promote colonization of the respiratory tract of compromised hosts. We have undertaken a genetic analysis of cable pili and have identified and characterized a locus, designated cbl, that encodes structural, accessory, and regulatory components of the cable pilus biosynthetic pathway. Within the cbl locus, three genes, designated cblS, cblT and cblR, are predicted to encode new members of the superfamily of environmentally responsive two-component signal transduction systems. The cblS and cblT genes encode membrane-bound sensor kinases and cblR encodes a DNA-binding transcription factor. We have insertionally inactivated each of the cblS, cblT, and cblR genes, and demonstrated that each is essential for cable pilus gene expression. We propose that CblS, CblT, and CblR together form a novel multichannel phosphorelay controlling cable pilus gene expression at the transcriptional level. We are utilizing a combined genetic and biochemical approach to characterize the function of individual components of the phosphorelay, and to define the signal transduction events controlling cable pilus gene expression.
Type III secretion in B. cenocepacia.
Pathogenesis in many gram-negative bacteria is dependent on the secretion of virulence proteins, called effectors, via a conserved secretory system, termed type III. We have identified and characterized a genetic locus encoding multiple type III secretion genes in B. cenocepacia. Using allelic exchange mutagenesis, we generated defined null mutations in central components of the type III secretion system and demonstrated that a type III mutant is severely attenuated in virulence in a murine model of infection. We are currently pursuing proteomic and genomic-based approaches to identify the secreted substrates of the B. cenocepacia type III translocon, as well as further characterize the role of type III secretion in modulating the host response to B. cenocepacia infection.
Role of B. cenocepacia flagella in cytokine induction, biofilm formation and swarming motility.
To gain further insight into the role of flagella as proinflammatory mediators and potentially important virulence determinants, we have generated aflagellar mutants in CF clinical isolates of B. cenocepacia and are using them to examine cytokine induction from infected human airway epithelial cells and to assess the role of motility in biofilm formation and a surface-associated form of movement known as swarming. Our findings indicate that flagellar biogenesis and motility promote B cenocepacia surface colonization, biofilm formation and induction of a host proinflammatory immune response that may contribute to infection and pathogenesis in CF patients.
