fur-independent regulation of the Pasteurella multocida hbpA gene encoding a haemin-binding protein

Fur activates the expression of Salmonella enterica pathogenicity island 1 by directly interacting with the hilD operator in vivo and in vitro

Previous studies have established that the expression of Salmonella enterica pathogenicity island 1 (SPI1), which is essential for epithelial invasion, is mainly regulated by the HilD protein. The ferric uptake regulator, Fur, in turn modulates the expression of the S. enterica hilD gene, albeit through an unknown mechanism. Here we report that S. enterica Fur, in its metal-bound form, specifically binds to an AT-rich region (BoxA), located upstream of the hilD promoter (P_hilD), at position -191 to -163 relative to the hilD transcription start site. Furthermore, in a P_hilD variant with mutations in BoxA, P_hilD*, Fur·Mn²⁺ binding is impaired. In vivo experiments using S. enterica strains carrying wild-type P_hilD or the mutant variant P_hilD* showed that Fur activates hilD expression, while in vitro experiments revealed that the Fur·Mn²⁺ protein is sufficient to increase hilD transcription. Together, these results present the first evidence that Fur·Mn²⁺, by binding to the upstream BoxA sequence, directly stimulates the expression of hilD in S. enterica.

Pasteurella multocidaand bovine respiratory disease

Pasteurella multocidais a pathogenic Gram-negative bacterium that has been classified into three subspecies, five capsular serogroups and 16 serotypes.P. multocidaserogroup A isolates are bovine nasopharyngeal commensals, bovine pathogens and common isolates from bovine respiratory disease (BRD), both enzootic calf pneumonia of young dairy calves and shipping fever of weaned, stressed beef cattle.P. multocidaA:3 is the most common serotype isolated from BRD, and these isolates have limited heterogeneity based on outer membrane protein (OMP) profiles and ribotyping. Development ofP. multocida-induced pneumonia is associated with environmental and stress factors such as shipping, co-mingling, and overcrowding as well as concurrent or predisposing viral or bacterial infections. Lung lesions consist of an acute to subacute bronchopneumonia that may or may not have an associated pleuritis. Numerous virulence or potential virulence factors have been described for bovine respiratory isolates including adherence and colonization factors, iron-regulated and acquisition proteins, extracellular enzymes such as neuraminidase, lipopolysaccharide, polysaccharide capsule and a variety of OMPs. Immunity of cattle against respiratory pasteurellosis is poorly understood; however, high serum antibodies to OMPs appear to be important for enhancing resistance to the bacterium. Currently availableP. multocidavaccines for use in cattle are predominately traditional bacterins and a live streptomycin-dependent mutant. The field efficacy of these vaccines is not well documented in the literature.

Analysis of the protective capacity of three Streptococcus suis proteins induced under divalent-cation-limited conditions

Streptococcus suis is a gram-positive pathogen that causes serious diseases in pigs and, in some cases, humans. Three genes of the virulent S. suis 89/1591 strain, encoding putative divalent-cation-binding lipoproteins, were isolated based on information obtained from the draft annotation files of this organism's genome. The products of these genes, which are inducible by divalent-cation deprivation, were subsequently purified, and their immunogenic and protective abilities were analyzed. All three proteins (SsuiDRAFT 0103, SsuiDRAFT 0174, and SsuiDRAFT 1237) were found to be immunogenic, but only one of them (SsuiDRAFT 0103) induced a significant protective response (87.5%, P = 0.01) against the same S. suis strain. Furthermore, the S. suis ssuiDRAFT 1240 gene (adcR), which encodes a predicted regulator of Zn2+ and/or Mn2+ uptake in streptococci, was cloned, and its protein product was purified. Electrophoretic mobility shift assays with purified S. suis AdcR protein showed experimentally, for the first time, that the AdcR DNA-binding sequence corresponds to the TTAACNRGTTAA motif. In addition, a requirement for either Zn2+ or Mn2+, but not Fe2+, to establish in vitro binding of AdcR to its target sequence and the ability of AdcR to bind the ssuiDRAFT 0103 and ssuiDRAFT 1237 gene promoters but not the promoter of the ssuiDRAFT 0174 gene were demonstrated. Taken together, these data suggest that SsuiDRAFT 0103 is a good candidate for vaccines against S. suis and support preliminary results indicating that bacterial envelope proteins involved in the uptake of divalent cations other than iron may be useful for protective purposes.

Porphyromonas gingivalis HmuY and HmuR: further characterization of a novel mechanism of heme utilization

Porphyromonas gingivalis HmuY is a putative heme-binding lipoprotein associated with the outer membrane. It is part of an operon together with a gene encoding an outer-membrane hemin utilization receptor (HmuR) and four uncharacterized genes. A similar operon organization was found in Bacteroides fragilis and B. thetaiotaomicron, with the former containing an additional HmuY homologue encoded upstream of the hmuR-like gene. In P. gingivalis cultured under heme-limited conditions, a approximately 1-kb hmuY transcript was produced at high levels along with some approximately 3.5 and approximately 9-kb transcripts. Compared with the parental strain, mutants deficient in hmuY or hmuR or hmuY-hmuR gene function grew more slowly and bound lower amounts of hemin and hemoglobin. Significantly, they grew more slowly or were unable to grow when human serum was used as the sole iron/heme source. Analysis of the hmu promoter showed that it is regulated by iron. The HmuY protein normally occurs as a homodimer, but in the presence of hemin it may form tetramers. These results show that HmuY may be the first reported member of a new class of proteins in Porphyromonas and Bacteroides species involved in heme utilization, a function being exerted in conjunction with HmuR, an outer-membrane heme transporter.

Comparative analysis of alterations in host phenotype and transcript accumulation following hypovirus and mycoreovirus infections of the chestnut blight fungus Cryphonectria parasitica

Infection of the chestnut blight fungus, Cryphonectria parasitica, by hypovirus CHV1-EP713 or by reovirus MyRV1-Cp9B21 or MyRV2-CpC18 results in reduced fungal virulence (hypovirulence). However, additional phenotypic changes caused by the two groups of mycoviruses are quite different. We now report that the loss of female fertility and the resulting absence of virus transmission through sexual spores observed after hypovirus infection was not observed for reovirus-infected C. parasitica. Consistent with this result, expression of two genes involved in sexual reproduction, the pheromone precursor gene, Mf2/1, and the yeast STE12-like transcriptional factor gene, cpst12, was less reduced in reovirus-infected strains than in the hypovirus CHV1-EP713-infected strain. Analysis with a custom microarray cDNA chip containing expressed sequence tag clones representing approximately 2,200 unique C. parasitica genes identified 140 and 128 host genes that were responsive to MyRV1-Cp9B21 or MyRV2-CpC18 infection, respectively. Comparison of these virus-responsive genes revealed an overlap of 85 genes, even though the nucleotide sequence identity for the two reoviruses is less than 50%. Significantly, 84 of the 85 genes were altered in the same direction. Further comparison revealed that 51% and 48% of the MyRV1-Cp9B21- and MyRV2-CpC18-responsive genes were also responsive to CHV1-EP713 infection. Finally, similar to results reported for CHV1-EP713 infection, a high percentage (59% and 66%) of the reovirus-responsive genes were also differentially expressed following disruption of the cellular G-protein signal transduction pathway. These data support the hypothesis that hypovirus and reovirus infections perturb common and specific C. parasitica regulatory pathways to cause hypovirulence and distinct sets of phenotypic changes.

Ste12 transcription factor homologue CpST12 is down-regulated by hypovirus infection and required for virulence and female fertility of the chestnut blight fungus Cryphonectria parasitica

A putative homologue of the Saccharomyces cerevisiae Ste12 transcription factor was identified in a series of expressed sequence tag-based microarray analyses as being down-regulated in strains of the chestnut blight fungus, Cryphonectria parasitica, infected by virulence-attenuating hypoviruses. Cloning of the corresponding gene, cpst12, confirmed a high level of similarity to Ste12 homologues of other filamentous fungi. Disruption of cpst12 resulted in no alterations in in vitro growth characteristics or colony morphology and an increase in the production of asexual spores, indicating that CpST12 is dispensable for vegetative growth and conidiation on artificial medium. However, the disruption mutants showed a very substantial reduction in virulence on chestnut tissue and a complete loss of female fertility, two symptoms normally conferred by hypovirus infection. Both virulence and female fertility were restored by complementation with the wild-type cpst12 gene. Analysis of transcriptional changes caused by cpst12 gene disruption with a custom C. parastica cDNA microaray chip identified 152 responsive genes. A significant number of these putative CpST12-regulated genes were also responsive to hypovirus infection. Thus, cpst12 encodes a cellular transcription factor, CpST12, that is down-regulated by hypovirus infection and required for female fertility, virulence and regulated expression of a subset of hypovirus responsive host genes.

Pasteurella multocida contains multiple immunogenic haemin- and haemoglobin-binding proteins

Iron-dependent outer membrane proteins (IROMPs) play an important role in bacterial pathogenesis and present several attributes of potential vaccine candidates. TBLASTN analysis of the Pasteurella multocida Pm70 genome using the same molecules of other bacterial pathogens as a query identified eight putative haemin and haemoglobin receptors for this organism. Quantitative binding assays have demonstrated that the proteins PM0040, PM0236, PM0741, PM1081, PM1428, PM0592 and HgbA bind both haemin and haemoglobin, whereas PM0576 and PM1282 ORFs only bind either haemoglobin or haemin, respectively. Furthermore, Western blot analysis showed that P. multocida-infected mice generate specific antibodies against PM0040, PM0236, PM0741, PM1081, PM1428, PM0592 and HgbA proteins. Nevertheless, inoculation of mice with any single one of these receptors alone did not protect against P. multocida infection.