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Results reveal that the signal transduction system component ArcB of Haemophilus influenzae although lacks the PAS domain, involved in signal reception of a variety of sensory proteins, still is capable of mediating signal transduction in response to growth conditions.

The complete DNA sequence of Pseudomonas aeruginosa provides an opportunity to apply functional genomics to a major human pathogen. A comparative genomics approach combined with genetic footprinting was used as a strategy to identify genes required for viability in P. aeruginosa. Use of a highly efficient in vivo mariner transposition system in P. aeruginosa facilitated the analysis of candidate genes of this class. We have developed a rapid and efficient allelic exchange system by using the I-Scel homing endonuclease in conjunction with in vitro mariner mutagenesis to generate mutants within targeted regions of the P. aeruginosa chromosome for genetic footprinting analyses. This technique for generating transposon insertion mutants should be widely applicable to other organisms that are not naturally transformable or may lack well developed in vivo transposition systems. We tested this system with three genes in P. aeruginosa that have putative essential homologs in Haemophilus influenzae. We show that one of three H. influenzae essential gene homologs is needed for growth in P. aeruginosa, validating the practicality of this comparative genomics strategy to identify essential genes in P. aeruginosa. transposon | SCE jumping

Nontypeable Haemophilus influenzae (NTHi) is a major cause of community acquired pneumonia and exacerbation of chronic obstructive pulmonary disease. A current effort in NTHi vaccine development has focused on generating humoral responses and has been greatly impeded by antigenic variation among the numerous circulating NTHi strains. In this study, we showed that pulmonary immunization of mice with killed NTHi generated broad protection against lung infection by different strains. While passive transfer of immune antibodies protected only against the homologous strain, transfer of immune T cells conferred protection against both homologous and heterologous strains. Further characterization revealed a strong Th17 response that was cross-reactive with different NTHi strains. Responding Th17 cells recognized both cytosolic and membrane-associated antigens, while immune antibodies preferentially responded to surface antigens and were highly strain specific. We further identified several conserved proteins recognized by lung Th17 cells during NTHi infection. Two proteins yielding the strongest responses were tested as vaccine candidates by immunization of mice with purified proteins plus an adjuvant. Immunization induced antigen-specific Th17 cells that recognized different strains and, upon adoptive transfer, conferred protection. Furthermore, immunized mice were protected against challenge with not only NTHi strains but also a fully virulent, encapsulated strain. Together, these results show that the immune mechanism of cross-protection against pneumonia involves Th17 cells, which respond to a broad spectrum of antigens, including those that are highly conserved among NTHi strains. These mechanistic insights suggest that inclusion of Th17 antigens in subunit vaccines offers the advantage of inducing broad protection and complements the current antibody-based approaches. [ABSTRACT FROM AUTHOR]

Rapid genome-wide identification of genes required for infection would expedite studies of bacterial pathogens. We developed genome-scale "negative selection" technology that combines high-density transposon mutagenesis and massively parallel sequencing of transposon/chromosome junctions in a mutant library to identify mutants lost from the library after exposure to a selective condition of interest. This approach was applied to comprehensively identify Haemophilus influenzae genes required to delay bacterial clearance in a murine pulmonary model. Mutations in 136 genes resulted in defects in vivo, and quantitative estimates of fitness generated by this technique were in agreement with independent validation experiments using individual mutant strains. Genes required in the lung included those with characterized functions in other models of H. influenzae pathogenesis and genes not previously implicated in infection. Genes implicated in vivo have reported or potential roles in survival during nutrient limitation, oxidative stress, and exposure to antimicrobial membrane perturbations, suggesting that these conditions are encountered by H. inf!uenzae during pulmonary infection. The results demonstrate an efficient means to identify genes required for bacterial survival in experimental models of pathogenesis, and this approach should function similarly well in selections conducted in vitro and in vivo with any organism amenable to insertional mutagenesis. [ABSTRACT FROM AUTHOR]

In response to environmental signals in the host, bacterial pathogens express factors required during infection and repress those that interfere with specific stages of this process. Signalling pathways controlling virulence factors of the human respiratory pathogen,Haemophilus influenzae,are predominantly unknown. The lipooligosaccharide (LOS) outer core represents a prototypical virulence trait ofH. influenzaethat enhances virulence but also provides targets for innate and adaptive immunity. We report regulation of the display of the virulence-associated phosphorylcholine (PC) epitope on the LOS in response to environmental conditions. PC display is optimal under microaerobic conditions and markedly decreased under conditions of high culture aeration. Gene expression analysis using a DNA microarray was performed to begin to define the metabolic state of the cell under these conditions and to identify genes potentially involved in PC epitope modulation. Global gene expression profiling detected changes in redox responsive genes and in genes of carbohydrate metabolism. The effects on carbohydrate metabolism led us to examine the role of the putativeH. influenzaehomologue ofcsrA, a regulator of glycolysis and gluconeogenesis inEscherichia coli. A mutant containing an in-frame deletion of theH. influenzae csrAgene showed increased PC epitope levels under aerobic conditions. Furthermore, deletion ofcsrAelevated mRNA expression ofgalU, an essential virulence gene that is critical in generating sugar precursors needed for polysaccharide formation and LOS outer core synthesis. Growth conditions predicted to alter the redox state of the culture modulated the PC epitope andgalUexpression as well. The results are consistent with a multifactorial mechanism of control of LOS-PC epitope display involvingcsrAand environmental signals that coordinately regulate biosynthetic and metabolic genes controlling the LOS structure. [ABSTRACT FROM AUTHOR]

As more microbial genome sequence information becomes available, the field of bacterial pathogenesis would benefit from the development of new genetic tools designed to facilitate gene function studies on a genomic scale. The complete DNA sequence of the bacterium Pseudomonas aeruginosa provides an opportunity to apply functional genomics to a major opportunistic human pathogen. Here, I describe the development of a new gene replacement scheme termed "SCE jumping" in P. aeruginosa. The system uses the yeast I-SceI homing endonuclease in conjunction with in vitro mariner-transposon mutagenesis to generate mutations within targeted regions of the chromosome for genetic footprinting. Use of SCE jumping for generating transposon insertion mutants is anticipated to be widely applicable to other bacterial organisms. This allelic exchange strategy, is discussed in context with other methods of gene replacement strategies available in P. aeruginosa. Development of SCE jumping provides an excellent example of the power of importing systems from unrelated organisms to circumvent practical challenges in molecular genetics. [ABSTRACT FROM AUTHOR]

Investigates through a genetic and biochemical approach the signal transduction pathway of the anoxic redox control (Arc) two-component system in Haemophilus influenza. Participation of the polyaluminum sulphate (PAS) domain in signal reception of a variety of proteins; Absence of PAS domain of the ArcB homolog in hemophilus influenza; Analysis of the signal transduction in response to redox conditions.

Whole-genome techniques toward identification of microbial genes required for their survival and growth during infection have been useful for studies of bacterial pathogenesis. The advent of massively parallel sequencing platforms has created the opportunity to markedly accelerate such genome-scale analyses and achieve unprecedented sensitivity, resolution, and quantification. This chapter provides an overview of a genome-scale methodology that combines high-density transposon mutagenesis with a mariner transposon and deep sequencing to identify genes that are needed for survival in experimental models of pathogenesis. Application of this approach to a model pathogen, Haemophilus influenzae, has provided a comprehensive analysis of the relative role of each gene of this human respiratory pathogen in a murine pulmonary model. The method is readily adaptable to nearly any organism amenable to transposon mutagenesis.

The human respiratory pathogen Haemophilus influenzae, a Gram-negative bacterium, is the first free-living organism to have its complete genome sequenced, providing the opportunity to apply genomic-scale approaches to study gene function. This chapter provides an overview of a highly efficient, in vitro mariner transposon-based method that exploits the natural transformation feature of this organism for the identification of essential genes. In addition, we describe strategies for conditional expression systems that would facilitate further analysis of this class of genes. Finally, we outline a method based on the approach used in H. influenzae for identifying essential genes that can be applied to other bacteria that are not naturally transformable.