Natural membrane vesicles (n-MVs) produced by Pseudomonas aeruginosa PAO1 and PAO1 carrying plasmid pAK1900 (p-MVs) were purified and analysed for DNA content. The MVs were isolated by a procedure designed to ensure no cellular contamination from the parent MV-producing cells. Fluorometry analysis revealed that p-MVs were associated with 7?80 ng DNA (20 mg MV protein)

The structural gene of the Pasteurella haemolytica leukotoxin determinant is highly homologous to that of the Escherichia coli hemolysin determinant, which also encodes a specialized set of genes involved in the secretion of the hemolysin. In this report, we describe the cloning and nucleotide sequence of the analogous secretion genes from P. haemolytica which make up the remainder of the leukotoxin determinant. The secretion genes were cloned directly from the P. haemolytica chromosome to form the recombinant plasmid pPH5B. By subcloning the secretion genes together with the leukotoxin structural gene, the cloned leukotoxin determinant was reconstructed on a single plasmid, pLKT52, which directs the synthesis of active leukotoxin to the culture supernatant when expressed in E. coli. DNA sequence analysis showed the presence of two secretion genes, designated lktB and lktD in order of their genetic organization, which code for proteins of 79.7-and 54.7 kilodaltons, both of which were detected when pLKT52 was expressed in E. coli minicells. The lktB and lktD genes were found to be highly homologous to the hlyB and hlyD secretion genes of the hemolysin determinant, and the predicted LktB-HlyB and LktD-HlyD proteins were 90.5 and 75.6% homologous. Nucleotide sequence homology between the leukotoxin and hemolysin determinants was limited to the C, A, B, and D coding regions, although the presence of similar transcriptional terminators in the A-B intercistronic region is suggestive of a similar transcriptional organization. On the basis of these data, we hypothesize that the two determinants share a common evolutionary history and are prototypes for a widely disseminated family of virulence factors, the RTX cytotoxins.

A 4.4-kilobase-pair DNA fragment coding for the leukotoxin of PasteureUa haemolytica Al has been isolated, and its nucleotide sequence has been determined. Two open reading frames, designated ikaC and IkUA, coding for proteins of 19.8 and 101.9 kilodaltons, respectively, were identified. Expression of the two genes in minicell-labeling experiments resulted in the production of the predicted proteins LKTC and LKTA. By using an antiserum against the soluble antigens of P. haemolytica Al in Western blot (immunoblot) analysis of total cellular proteins from the Escherichia coli clones, LKTA was identified as an additional antigenic protein. Results from subcloning of the DNA fragment suggested that expression from both lkiC and lktA is required for leukotoxin activity, indicating that the leukotoxin of P. haemolylica Al is encoded by two genes. A comparison of the organization and the DNA sequence of the leukotoxin genes with those of the E. coli alpha-hemolysin genes showed a significant degree of homology between the two loci. This analysis suggested that the leukotoxin genes of P. haemolylica Al and the E. coli alpha-hemolysin genes may have evolved from a common ancestor and that the two toxins may share similar activities or functional domains or both.

The draft genome sequence of Mannheimia haemolytica A1, the causative agent of bovine respiratory disease complex (BRDC), is presented. Strain ATCC BAA-410, isolated from the lung of a calf with BRDC, was the DNA source. The annotated genome includes 2,839 coding sequences, 1,966 of which were assigned a function and 436 of which are unique to M. haemolytica. Through genome annotation many features of interest were identified, including bacteriophages and genes related to virulence, natural competence, and transcriptional regulation. In addition to previously described virulence factors, M. haemolytica encodes adhesins, including the filamentous hemagglutinin FhaB and two trimeric autotransporter adhesins. Two dual-function immunoglobulin-protease/adhesins are also present, as is a third immunoglobulin protease. Genes related to iron acquisition and drug resistance were identified and are likely important for survival in the host and virulence. Analysis of the genome indicates that M. haemolytica is naturally competent, as genes for natural competence and DNA uptake signal sequences (USS) are present. Comparison of competence loci and USS in other species in the family Pasteurellaceae indicates that M. haemolytica, Actinobacillus pleuropneumoniae, and Haemophilus ducreyi form a lineage distinct from other Pasteurellaceae. This observation was supported by a phylogenetic analysis using sequences of predicted housekeeping genes.Mannheimia haemolytica serotype A1 is the principle bacterial pathogen associated with bovine respiratory disease complex, also known as bovine shipping fever (25, 31). M. haemolytica resides in the upper respiratory tracts of healthy ruminants, although in immunocompromised animals, such as those with a preexisting viral infection, M. haemolytica can descend into the lungs, leading to pneumonia. The mortality and morbidity associated with this disease cause substantial losses to the cattle industry (25, 31). Hence, much research on M. haemolytica is directed at understanding its virulence and designing vaccines to protect cattle (31).M. haemolytica is a member of the family Pasteurellaceae, which is classified among the ␥-proteobacteria and includes human and animal pathogens of the genera Mannheimia, Pasteurella, Haemophilus, Actinobacillus, and Histophilus (31). M. haemolytica (formerly Pasteurella haemolytica) is classified in the genus Mannheimia based upon 16S rRNA sequence phylogeny and DNA-DNA hybridizations (3). The family Pasteurellaceae includes several members whose genomes have been sequenced: Haemophilus influenzae, Pasteurella multocida, Mannheimia succiniciproducens, Actinobacillus pleuropneumoniae, Histophilus somni, Haemophilus ducreyi, and Actinobacillus actinomycetemcomitans.The primary virulence factor of M. haemolytica is considered the leukotoxin. It is a calcium-dependent toxin that is a member of the RTX family of toxins. Cytolytic at low concentrations and apoptotic at high concentrations, the leukotoxin provokes an inflammatory response that can lead to intense ed...

Pasteurella haemolytica serotype Al secretes a glycoprotease which is specific for 0-sialoglycoproteins such as glycophorin A. The gene encoding the glycoprotease enzyme has been cloned in the recombinant plasmid pPHl, and its nucleotide sequence has been determined. The gene (designated gcp) codes for a protein of 35.2 kDa, and an active enzyme protein of this molecular mass can be observed in Escherichia coli clones carrying pPHl. In vivo labeling of plasmid-encoded proteins in E. coli maxicells demonstrated the expression of a 35-kDa protein from pPHl. The amino-terminal sequence of the heterologously expressed protein corresponds to that predicted from the nucleotide sequence. The glycoprotease is a neutral metalloprotease, and the predicted amino acid sequence of the glycoprotease contains a putative zinc-binding site. The gene shows no significant homology with the genes for other proteases of procaryotic or eucaryotic origin. However, there is substantial homology between gcp and an E. coli gene, orJX, whose product is believed to function in the regulation of macromolecule biosynthesis.