Mannheimia cairinae sp. nov., a novel species of Mannheimia obtained from Muscovy ducks (Cairina moschata) and reclassification of Mannheimia ovis as heterotypic synonym of Mannheimia pernigra

During a screening study for Pasteurella multocida in two unrelated flocks of Muscovy ducks pharyngeal and cloacal swabs were collected. A total of 59 Pasteurellaceae-like isolates sharing the same colony morphology were subcultured and subsequently characterized. Colonies on bovine blood agar were nonhaemolytic, regular, circular, slightly raised, shiny, intransparent with an entire margin, greyish and had an unguent-like consistency. Isolate AT1T was characterized by 16S rRNA gene sequencing and showed the highest similarity of 96.1 % to the type strain of Mannheimia caviae and 96.0 % to the type strain of Mannheimia bovis, respectively. In addition, rpoB and recN gene sequences also showed the highest similarity to the genus Mannheimia. The phylogenetic comparison of concatenated conserved protein sequences also showed a unique position of AT1T compared to other species of Mannheimia. Full phenotypic characterization of the isolates showed that between two (Mannheimia ruminalis) and 10 (Mannheimia glucosida) phenotypic characteristics separate the taxon isolated from Muscovy ducks from the accepted species of Mannheimia. Whole genomic sequences of two strains analysed by the type strain genome server showed the highest similarity of 24.9 % to the genome of the type strain of Pasteurella multocida and 23.0 % to the genome of the type strain of Mannheimia haemolytica. The species Mannheimia cairinae sp. nov. is proposed based on the phenotypic and genotypic similarity to Mannheimia as well as differences to the other validly published species of the genus. The leukotoxin protein was not predicted in the genome of AT1T. The G+C content of the type strain of M. cairinae sp. nov., AT1T (=CCUG 76754T=DSM 115341T) is 37.99 mol%, calculated from the whole genome. The investigation further proposes that Mannheimia ovis is reclassified as a later heterotypic synonym of Mannheimia pernigra, since M. ovis and M. pernigra are closely genetically related, and M. pernigra was validly published before M. ovis.

Human Wound Infection with Mannheimia glucosida following Lamb Bite

Mannheimia spp. are veterinary pathogens that can cause mastitis and pneumonia in domestic cattle and sheep. While Mannheimia glucosida can be found as normal flora in oral and respiratory mucosa in sheep, there have been no reported cases of human infection with this organism.

[Fatty acid composition of cells and lipopolysaccliarides of Mannheimia haemolytica, Mannheimia glucosida and Bibersteinia trehalosi strains]

The Mannheimia haemolytica, Mannheimia glucosida and Bibersteinia trehalosi strains and the similar fatty acid composition of cells with domination of C(16:1) and C(16:0), which were in almost equal quantities, C(14:0 and C(18:1) + C(18:2). The fatty acid composition of lipopolysaccharides (LPS) of the studied bacteria had no essential differences too. It was mainly represented by C(14:0) and 3-OH-C(14:0) which consisted of more than 80% of all LPS fatty acids. C(12:0), C(16:1) and C(16:0) were presented in LPS in small quantities. The M. haemolytica, M. glucosida and B. trehalosi strains did not differ essentially by fatty acid compositions of cells and LPS from earlier studied strains of genera Pasteurella (P. multocida), Haemophilus (H. influenzae and other species), Actinobacillus (A. pleuropneumoniae). This shows the close phylogenetic relationship of the mentioned bacteria and significance of investigated signs as chemotaxonomic markers for differentiation of taxons of the above genus level. The paper is presented in Russian.

Succinic acid production from continuous fermentation process using Mannheimia succiniciproducens LPK7

To achieve a higher succinic acid productivity and evaluate the industrial applicability, this study used Mannheimia succiniciproducens LPK7 (knock-out: lahA, pflB, pta-ackA), which was recently designed to enhance the productivity of succinic acid and reduce by-product secretion. Anaerobic continuous fermentation of Mannheimia succiniciproducens LPK7 was carried out at different glucose feed concentrations and dilution rates. After extensive fermentation experiments, a succinic acid yield and productivity of 0.38 mol/mol and 1.77 g/l/h, respectively, were achieved with a glucose feed concentration of 18.0 g/l and 0.2 h-1 dilution rate. A similar amount of succinic acid production was also produced in batch culture experiments. Therefore, these optimal conditions can be industrially applied for the continuous production of succinic acid. To examine the quantitative balance of the metabolism, a flux distribution analysis was also performed using the metabolic network model of glycolysis and the pentose phosphate pathway.

Identification of a novel Mannheimia granulomatis lineage from lesions in roe deer (Capreolus capreolus)

Eight atypical Mannheimia isolates were isolated from lesions in roe deer (Capreolus capreolus). Traditional classification based on morphologic and physiologic traits showed that they belong to a distinct biogroup (taxon) within genus Mannheimia. Extensive phenotypic characterization suggested that the isolates should be classified as M. granulomatis, although the presence of distinct traits justified their classification into a separate biogroup within this species. Phylogenetic analyses based on 16S rRNA sequences from two roe deer isolates and 41 other Mannheimia strains supported that the roe deer isolates form a monophyletic group within M. granulomatis. The lktA genotype was present in all roe deer isolates based on Southern blot analysis, whereas the corresponding beta-hemolytic phenotype was absent in one of these isolates.

Analysis of gene order data supports vertical inheritance of the leukotoxin operon and genome rearrangements in the 5' flanking region in genus Mannheimia

Background

The Mannheimia subclades belong to the same bacterial genus, but have taken divergent paths toward their distinct lifestyles. For example, M. haemolytica + M. glucosida are potential pathogens of the respiratory tract in the mammalian suborder Ruminantia, whereas M. ruminalis, the supposed sister group, lives as a commensal in the ovine rumen. We have tested the hypothesis that vertical inheritance of the leukotoxin (lktCABD) operon has occurred from the last common ancestor of genus Mannheimia to any ancestor of the diverging subclades by exploring gene order data.

Results

We examined the gene order in the 5' flanking region of the leukotoxin operon and found that the 5' flanking gene strings, hslVU-lapB-artJ-lktC and xylAB-lktC, are peculiar to M. haemolytica + M. glucosida and M. granulomatis, respectively, whereas the gene string hslVU-lapB-lktC is present in M. ruminalis, the supposed sister group of M. haemolytica + M. glucosida, and in the most ancient subclade M. varigena. In M. granulomatis, we found remnants of the gene string hslVU-lapB-lktC in the xylB-lktC intergenic region.

Conclusion

These observations indicate that the gene string hslVU-lapB-lktC is more ancient than the hslVU-lapB-artJ-lktC and xylAB-lktC gene strings. The presence of (remnants of) the ancient gene string hslVU-lapB-lktC among any subclades within genus Mannheimia supports that it has been vertically inherited from the last common ancestor of genus Mannheimia to any ancestor of the diverging subclades, thus reaffirming the hypothesis of vertical inheritance of the leukotoxin operon. The presence of individual 5' flanking regions in M. haemolytica + M. glucosida and M. granulomatis reflects later genome rearrangements within each subclade. The evolution of the novel 5' flanking region in M. haemolytica + M. glucosida resulted in transcriptional coupling between the divergently arranged artJ and lkt promoters. We propose that the chimeric promoter have led to high level expression of the leukotoxin operon which could explain the increased potential of certain M. haemolytica + M. glucosida strains to cause a particular type of infection.

Nucleotide sequence and transfer properties of two novel types of Actinobacillus pleuropneumoniae plasmids carrying the tetracycline resistance gene tet(H)

OBJECTIVES

To analyse the sequence and transfer properties of two tetracycline resistance plasmids found in clinical isolates of Actinobacillus pleuropneumoniae in order to assess their role in the spread of tetracycline resistance.

METHODS

The plasmids designated p9956 and p12494 were purified from A. pleuropneumoniae and completely sequenced. The transfer properties of both plasmids were evaluated by electroporation and/or conjugation into Pasteurella multocida and Escherichia coli.

RESULTS

Both plasmids showed a modular structure consisting of three regions involved in mobilization, tetracycline resistance or replication. The mobilization regions included the mobA gene, encoding a relaxase, a protein involved in plasmid transfer. The tetracycline resistance regions were closely related and consisted of the tet(H) gene and its repressor gene tetR. The tetracycline resistance phenotype was transferred successfully to P. multocida and in the case of p9956 also to E. coli by electroporation of the plasmids. Moreover, plasmid p9956 could be mobilized in E. coli with the assistance of RP4 conjugal transfer functions.

CONCLUSIONS

For the first time, the complete sequences of two tet(H)-carrying plasmids from A. pleuropneumoniae were determined. These two plasmids differed from one another and from known tet(H)-carrying plasmids from Pasteurella or Mannheimia spp. Structural analysis confirmed that these plasmids consisted of segments that have been previously detected in members of the families Pasteurellaceae and Enterobacteriaceae.

Genome-scale analysis of Mannheimia succiniciproducens metabolism

Mannheimia succiniciproducens MBEL55E isolated from bovine rumen is a capnophilic gram-negative bacterium that efficiently produces succinic acid, an industrially important four carbon dicarboxylic acid. In order to design a metabolically engineered strain which is capable of producing succinic acid with high yield and productivity, it is essential to optimize the whole metabolism at the systems level. Consequently, in silico modeling and simulation of the genome-scale metabolic network was employed for genome-scale analysis and efficient design of metabolic engineering experiments. The genome-scale metabolic network of M. succiniciproducens consisting of 686 reactions and 519 metabolites was constructed based on reannotation and validation experiments. With the reconstructed model, the network structure and key metabolic characteristics allowing highly efficient production of succinic acid were deciphered; these include strong PEP carboxylation, branched TCA cycle, relative weak pyruvate formation, the lack of glyoxylate shunt, and non-PTS for glucose uptake. Constraints-based flux analyses were then carried out under various environmental and genetic conditions to validate the genome-scale metabolic model and to decipher the altered metabolic characteristics. Predictions based on constraints-based flux analysis were mostly in excellent agreement with the experimental data. In silico knockout studies allowed prediction of new metabolic engineering strategies for the enhanced production of succinic acid. This genome-scale in silico model can serve as a platform for the systematic prediction of physiological responses of M. succiniciproducens to various environmental and genetic perturbations and consequently for designing rational strategies for strain improvement.

Construction and characterization of shuttle vectors for succinic acid-producing rumen bacteria

Shuttle vectors carrying the origins of replication that function in Escherichia coli and two capnophilic rumen bacteria, Mannheimia succiniciproducens and Actinobacillus succinogenes, were constructed. These vectors were found to be present at ca. 10 copies per cell. They were found to be stably maintained in rumen bacteria during the serial subcultures in the absence of antibiotic pressure for 216 generations. By optimizing the electroporation condition, the transformation efficiencies of 3.0 x 10(6) and 7.1 x 10(6) transformants/mug DNA were obtained with M. succiniciproducens and A. succinogenes, respectively. A 1.7-kb minimal replicon was identified that consists of the rep gene, four iterons, A+T-rich regions, and a dnaA box. It was found that the shuttle vector replicates via the theta mode, which was confirmed by sequence analysis and Southern hybridization. These shuttle vectors were found to be suitable as expression vectors as the homologous fumC gene encoding fumarase and the heterologous genes encoding green fluorescence protein and red fluorescence protein could be expressed successfully. Thus, the shuttle vectors developed in this study should be useful for genetic and metabolic engineering of succinic acid-producing rumen bacteria.

Evidence for Vertical Inheritance and Loss of the Leukotoxin Operon in Genus Mannheimia

The Mannheimia subclades belong to the same bacterial genus but have taken divergent paths toward their distinct lifestyles. M. haemolytica + M. glucosida are potential pathogens of the respiratory tract in the mammalian suborder Ruminantia, whereas M. ruminalis, the supposed sister group, lives as a commensal in the ovine rumen. We have tested the hypothesis that horizontal gene transfer of the leukotoxin operon has catalyzed pathogenic adaptation and speciation of M. haemolytica + M. glucosida, or other major subclades, by using a strategy that combines compositional and phylogenetic methods. We show that it has been vertically inherited from the last common ancestor of the diverging Mannheimia subclades, although several strains belonging to M. ruminalis have lost the operon. Our analyses support that divergence within M. ruminalis following colonization of the ovine rumen was very rapid and that functional decay of most of the leukotoxin operons occurred early when the adaptation to the rumen was fastest, suggesting that antagonistic pleiotropy was the main contributor to losses in the radiating lineages of M. ruminalis. To sum up, the scenario derived from these analyses reflects two aspects. On one hand, it opposes the hypothesis of horizontal gene transfer as a catalyst of pathogenic adaptation and speciation. On the other hand, it indicates that losses of the leukotoxin operons in the radiating lineages of M. ruminalis have catalyzed their adaptation to a commensal environment and reproductive isolation (speciation).

Occurrence of haemolytic Mannheimia spp. in apparently healthy sheep in Norway

Background

The occurrence of Mannheimia species in healthy sheep has only been investigated to a very limited extend since the genus and its five named species were established. The aim of the present study was to evaluate the occurrence of haemolytic Mannheimia species in apparently healthy sheep originating from four sheep flocks in South-Western Norway.

Methods

Typical β-haemolytic Pasteurellaceae were isolated from nasal swabs and subsequently subjected to bacteriological examination. A total of 57 Mannheimia isolates were obtained in pure culture. All isolates were genotyped by amplified fragment length polymorphisms (AFLP) analysis and compared to six reference strains. The 16S rRNA gene sequences of two isolates were also determined.

Results

β-haemolytic Mannheimia species were isolated from 24% to 64% of the sheep in the four flocks. A total of 26 haemolytic M. ruminalis-like strains were isolated among which, a considerable genetic diversity was found. Eighteen M. glucosida isolates were obtained from three flocks, whereas M. haemolytica was only isolated from two flocks, 16 of them being from only one of the flocks.

Conclusion

We demonstrate that a relatively high number of apparently healthy sheep in Norway seem to carry the potentially pathogenic M. haemolytica and M. glucosida in the upper respiratory tract. An unexpectedly high number of haemolytic M. ruminalis-like organisms were also obtained in all four flocks. The usually non-haemolytic M. ruminalis are typically isolated from healthy ruminants. The significance of β-haemolytic M. ruminalis-like organisms is unknown and should be investigated in a future study.

The proteome ofMannheimia succiniciproducens, a capnophilic rumen bacterium

Mannheimia succiniciproducens MBEL55E isolated from bovine rumen is an industrially important bacterium as an efficient succinic acid producer. Recently, its full genome sequence was determined. In the present study, we analyzed the M. succiniciproducens proteome based on the genome information using 2-DE and MS. We established proteome reference map of M. succiniciproducens by analyzing whole cellular proteins, membrane proteins, and secreted proteins. More than 200 proteins were identified and characterized by MS/MS supported by various bioinformatic tools. The presence of proteins previously annotated as hypothetical proteins or proteins having putative functions were also confirmed. Based on the proteome reference map, cells in the different growth phases were analyzed at the proteome level. Comparative proteome profiling revealed valuable information to understand physiological changes during growth, and subsequently suggested target genes to be manipulated for the strain improvement.

Genome-based metabolic engineering of Mannheimia succiniciproducens for succinic acid production

Succinic acid is a four-carbon dicarboxylic acid produced as one of the fermentation products of anaerobic metabolism. Based on the complete genome sequence of a capnophilic succinic acid-producing rumen bacterium, Mannheimia succiniciproducens, gene knockout studies were carried out to understand its anaerobic fermentative metabolism and consequently to develop a metabolically engineered strain capable of producing succinic acid without by-product formation. Among three different CO2-fixing metabolic reactions catalyzed by phosphoenolpyruvate (PEP) carboxykinase, PEP carboxylase, and malic enzyme, PEP carboxykinase was the most important for the anaerobic growth of M. succiniciproducens and succinic acid production. Oxaloacetate formed by carboxylation of PEP was found to be converted to succinic acid by three sequential reactions catalyzed by malate dehydrogenase, fumarase, and fumarate reductase. Major metabolic pathways leading to by-product formation were successfully removed by disrupting the ldhA, pflB, pta, and ackA genes. This metabolically engineered LPK7 strain was able to produce 13.4 g/liter of succinic acid from 20 g/liter glucose with little or no formation of acetic, formic, and lactic acids, resulting in a succinic acid yield of 0.97 mol succinic acid per mol glucose. Fed-batch culture of M. succiniciproducens LPK7 with intermittent glucose feeding allowed the production of 52.4 g/liter of succinic acid, with a succinic acid yield of 1.16 mol succinic acid per mol glucose and a succinic acid productivity of 1.8 g/liter/h, which should be useful for industrial production of succinic acid.

tet(L)-mediated tetracycline resistance in bovine Mannheimia and Pasteurella isolates

OBJECTIVES

Tetracycline-resistant Mannheimia and Pasteurella isolates, which were negative for the tetracycline resistance genes (tet) commonly detected among these bacteria, were investigated for other tet genes present and their location.

METHODS

Mannheimia and Pasteurella isolates were investigated for their MICs of tetracycline and their plasmid content. Identification of tet genes was achieved by PCR. Plasmids mediating tetracycline resistance were identified by transformation and hybridization experiments. Plasmid pCCK3259 from Mannheimia haemolytica was sequenced completely and analysed for its structure and organization.

RESULTS

All tetracycline-resistant isolates carried the gene tet(L) either on plasmids or on the chromosome. Two M. haemolytica isolates and one Mannheimia glucosida isolate harboured a common 5.3 kb tet(L) plasmid, designated pCCK3259. This plasmid was similar to the tet(B)-carrying tetracycline resistance plasmid pHS-Tet from Haemophilus parasuis and the streptomycin/spectinomycin resistance plasmid pCCK647 from Pasteurella multocida in the parts coding for mobilization functions. The tet(L) gene was closely related to that of the Geobacillus stearothermophilus plasmid pTB19. However, the translational attenuator responsible for the tetracycline-inducible expression of tet(L) was missing in plasmid pCCK3259. A recombination site was identified downstream of tet(L), which might explain the integration of the tet(L) gene region into a basic pCCK3259 replicon.

CONCLUSION

A tet(L) gene was shown for the first time to be responsible for tetracycline resistance in Mannheimia and Pasteurella isolates. This report demonstrates a lateral transfer of a tetracycline efflux gene in Gram-negative bovine respiratory tract pathogens, probably originating from Gram-positive bacteria.

Comparative phylogenies of the housekeeping genes atpD, infB and rpoB and the 16S rRNA gene within the Pasteurellaceae

Phylogenies of housekeeping gene and 16S rRNA gene sequences were compared to improve the classification of the bacterial family Pasteurellaceae and knowledge of the evolutionary relationships of its members. Deduced partial protein sequences of the housekeeping genes atpD, infB and rpoB were compared in 28, 36 and 28 representative taxa of the Pasteurellaceae, respectively. The monophyly of representatives of the genus Gallibacterium was recognized by analysis of all housekeeping genes, while members of Mannheimia, Actinobacillus sensu stricto and the core group of Pasteurella sensu stricto formed monophyletic groups with two out of three housekeeping genes. Representatives of Mannheimia, Actinobacillus sensu stricto, [Haemophilus] ducreyi and [Pasteurella] trehalosi formed a monophyletic unit by analysis of all three housekeeping genes, which was in contrast to the 16S rRNA gene-derived phylogeny, where these taxa occurred at separate positions in the phylogenetic tree. Representatives of the Rodent, Avian and Aphrophilus-Haemophilus 16S rRNA gene groups were weakly supported by phylogenetic analysis of housekeeping genes. Phylogenies derived by comparison of the housekeeping genes diverged significantly from the 16S rRNA gene-derived phylogeny as evaluated by the likelihood ratio test. A low degree of congruence was also observed between the individual housekeeping gene-derived phylogenies. Estimates on speciation derived from 16S rRNA and housekeeping gene sequence comparisons resulted in quite different evolutionary scenarios for members of the Pasteurellaceae. The phylogeny based on the housekeeping genes supported observed host associations between Mannheimia, Actinobacillus sensu stricto and [Pasteurella] trehalosi and animals with paired hooves.

Fatal meningitis in a calf caused by Mannheimia varigena

Mannheimia varigena was identified as the etiologic agent of meningitis in a young Belgian White Blue heifer calf. Species identification of the bacterium was done by phenotyping and molecularly confirmed by tDNA-PCR. Standard bacteriological examination might fail to differentiate species belonging to the genus Mannheimia.

Sequence diversity and molecular evolution of the heat-modifiable outer membrane protein gene (ompA) of Mannheimia(Pasteurella) haemolytica, Mannheimia glucosida, and Pasteurella trehalosi

The OmpA (or heat-modifiable) protein is a major structural component of the outer membranes of gram-negative bacteria. The protein contains eight membrane-traversing beta-strands and four surface-exposed loops. The genetic diversity and molecular evolution of OmpA were investigated in 31 Mannheimia (Pasteurella) haemolytica, 6 Mannheimia glucosida, and 4 Pasteurella trehalosi strains by comparative nucleotide sequence analysis. The OmpA proteins of M. haemolytica and M. glucosida contain four hypervariable domains located at the distal ends of the surface-exposed loops. The hypervariable domains of OmpA proteins from bovine and ovine M. haemolytica isolates are very different but are highly conserved among strains from each of these two host species. Fourteen different alleles representing four distinct phylogenetic classes, classes I to IV, were identified in M. haemolytica and M. glucosida. Class I, II, and IV alleles were associated with bovine M. haemolytica, ovine M. haemolytica, and M. glucosida strains, respectively, whereas class III alleles were present in certain M. haemolytica and M. glucosida isolates. Class I and II alleles were associated with divergent lineages of bovine and ovine M. haemolytica strains, respectively, indicating a history of horizontal DNA transfer and assortative (entire gene) recombination. Class III alleles have mosaic structures and were derived by horizontal DNA transfer and intragenic recombination. Our findings suggest that OmpA is under strong selective pressure from the host species and that it plays an important role in host adaptation. It is proposed that the OmpA protein of M. haemolytica acts as a ligand and is involved in binding to specific host cell receptor molecules in cattle and sheep. P. trehalosi expresses two OmpA homologs that are encoded by different tandemly arranged ompA genes. The P. trehalosi ompA genes are highly diverged from those of M. haemolytica and M. glucosida, and evidence is presented to suggest that at least one of these genes was acquired by horizontal DNA transfer.

The genome sequence of the capnophilic rumen bacterium Mannheimia succiniciproducens

The rumen represents the first section of a ruminant animal's stomach, where feed is collected and mixed with microorganisms for initial digestion. The major gas produced in the rumen is CO(2) (65.5 mol%), yet the metabolic characteristics of capnophilic (CO(2)-loving) microorganisms are not well understood. Here we report the 2,314,078 base pair genome sequence of Mannheimia succiniciproducens MBEL55E, a recently isolated capnophilic Gram-negative bacterium from bovine rumen, and analyze its genome contents and metabolic characteristics. The metabolism of M. succiniciproducens was found to be well adapted to the oxygen-free rumen by using fumarate as a major electron acceptor. Genome-scale metabolic flux analysis indicated that CO(2) is important for the carboxylation of phosphoenolpyruvate to oxaloacetate, which is converted to succinic acid by the reductive tricarboxylic acid cycle and menaquinone systems. This characteristic metabolism allows highly efficient production of succinic acid, an important four-carbon industrial chemical.

tRNA-intergenic spacer PCR for the identification of Pasteurella and Mannheimia spp

tRNA-intergenic spacer PCR (tDNA-PCR) was evaluated for its effectiveness in differentiating Pasteurella and Mannheimia (sub)species predominantly of ruminant origin. For this purpose, 38 reference strains and 13 field isolates belonging to both genera were investigated. tDNA-PCR enabled discrimination of all Pasteurella species tested (Pasteurella (P.) aerogenes, P. avium, P. canis, P. lymphangitidis, P. multocida, P. trehalosi). For the differentiation of the subspecies of P. multocida, an additional dulcitol reaction was required. Two of the five so far-defined Mannheimia species, M. granulomatis and M. varigena, had a distinct fingerprinting profile. The remaining three phylogenetically highly related species (M. haemolytica, M. glucosida, and M. ruminalis) clustered together. Nevertheless, M. ruminalis is non-haemolytic, and M. haemolytica and M. glucosida can be differentiated on the basis of two additional phenotypic characteristics (beta-glucosidase and aesculin hydrolysis). In conclusion, tDNA-PCR is a useful tool in differentiating organisms belonging to the genera Pasteurella and Mannheimia.