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Omp2b Porin Alteration in the Course of Evolution of Brucella spp.

ABSTRACT: The genus Brucella comprises major pathogenic species causing disease in livestock and humans, e.g. B. melitensis. In the past few years, the genus has been significantly expanded by the discovery of phylogenetically more distant lineages comprising strains from diverse wildlife animal species, including amphibians and fish. The strains represent several potential new species, with B. inopinata as solely named representative. Being genetically more distant between each other, relative to the "classical" Brucella species, they present distinct atypical phenotypes and surface antigens. Among surface protein antigens, the Omp2a and Omp2b porins display the highest diversity in the classical Brucella species. The genes coding for these proteins are closely linked in the Brucella genome and oriented in opposite directions. They share between 85 and 100% sequence identity depending on the Brucella species, biovar, or genotype. Only the omp2b gene copy has been shown to be expressed and genetic variation is extensively generated by gene conversion between the two copies. In this study, we analyzed the omp2 loci of the non-classical Brucella spp. Starting from two distinct ancestral genes, represented by Australian rodent strains and B. inopinata, a stepwise nucleotide reduction was observed in the omp2b gene copy. It consisted of a first reduction affecting the region encoding the surface L5 loop of the porin, previously shown to be critical in sugar permeability, followed by a nucleotide reduction in the surface L8 loop-encoding region. It resulted in a final omp2b gene size shared between two distinct clades of non-classical Brucella spp. (African bullfrog isolates) and the group of classical Brucella species. Further evolution led to complete homogenization of both omp2 gene copies in some Brucella species such as B. vulpis or B. papionis. The stepwise omp2b deletions seemed to be generated through recombination with the respective omp2a gene copy, presenting a conserved size among Brucella spp., and may involve short direct DNA repeats. Successive Omp2b porin alteration correlated with increasing porin permeability in the course of evolution of Brucella spp. They possibly have adapted their porin to survive environmental conditions encountered and to reach their final status as intracellular pathogen.

SUBMITTER: Cloeckaert A

PROVIDER: S-EPMC7050475 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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Omp2b Porin Alteration in the Course of Evolution of Brucella spp.

Cloeckaert Axel A Vergnaud Gilles G Zygmunt Michel S MS

Frontiers in microbiology 20200224

The genus Brucella comprises major pathogenic species causing disease in livestock and humans, e.g. B. melitensis. In the past few years, the genus has been significantly expanded by the discovery of phylogenetically more distant lineages comprising strains from diverse wildlife animal species, including amphibians and fish. The strains represent several potential new species, with B. inopinata as solely named representative. Being genetically more distant between each other ...[more]

PMID: 32153552

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Project description:BACKGROUND: Brucella is an intracellular pathogen capable of infecting animals and humans. There are six recognized species of Brucella that differ in their host preference. The genomes of the three Brucella species have been recently sequenced. Comparison of the three revealed over 98% sequence similarity at the protein level and enabled computational identification of common and differentiating genes. We validated these computational predictions and examined the expression patterns of the putative unique and differentiating genes, using genomic and reverse transcription PCR. We then screened a set of differentiating genes against classical Brucella biovars and showed the applicability of these regions in the design of diagnostic tests. RESULTS: We have identified and tested set of molecular targets that are associated in unique patterns with each of the sequenced Brucella spp. A comprehensive comparison was made among the published genome sequences of B. abortus, B. melitensis and B. suis. The comparison confirmed published differences between the three Brucella genomes, and identified subsets of features that were predicted to be of interest in a functional comparison of B. melitensis and B. suis to B. abortus. Differentiating sequence regions from B. abortus, B. melitensis and B. suis were used to develop PCR primers to test for the existence and in vitro transcription of these genes in these species. Only B. suis is found to have a significant number of unique genes, but combinations of genes and regions that exist in only two out of three genomes and are therefore useful for diagnostics were identified and confirmed. CONCLUSION: Although not all of the differentiating genes identified were transcribed under steady state conditions, a group of genes sufficient to discriminate unambiguously between B. suis, B. melitensis, and B. abortus was identified. We present an overview of these genomic differences and the use of these features to discriminate among a number of Brucella biovars.

Project description:Two Gram-negative, non-motile, non-spore-forming coccoid bacteria (strains F8/08-60(T) and F8/08-61) isolated from clinical specimens obtained from baboons (Papio spp.) that had delivered stillborn offspring were subjected to a polyphasic taxonomic study. On the basis of 16S rRNA gene sequence similarities, both strains, which possessed identical sequences, were assigned to the genus Brucella. This placement was confirmed by extended multilocus sequence analysis (MLSA), where both strains possessed identical sequences, and whole-genome sequencing of a representative isolate. All of the above analyses suggested that the two strains represent a novel lineage within the genus Brucella. The strains also possessed a unique profile when subjected to the phenotyping approach classically used to separate species of the genus Brucella, reacting only with Brucella A monospecific antiserum, being sensitive to the dyes thionin and fuchsin, being lysed by bacteriophage Wb, Bk2 and Fi phage at routine test dilution (RTD) but only partially sensitive to bacteriophage Tb, and with no requirement for CO2 and no production of H2S but strong urease activity. Biochemical profiling revealed a pattern of enzyme activity and metabolic capabilities distinct from existing species of the genus Brucella. Molecular analysis of the omp2 locus genes showed that both strains had a novel combination of two highly similar omp2b gene copies. The two strains shared a unique fingerprint profile of the multiple-copy Brucella-specific element IS711. Like MLSA, a multilocus variable number of tandem repeat analysis (MLVA) showed that the isolates clustered together very closely, but represent a distinct group within the genus Brucella. Isolates F8/08-60(T) and F8/08-61 could be distinguished clearly from all known species of the genus Brucella and their biovars by both phenotypic and molecular properties. Therefore, by applying the species concept for the genus Brucella suggested by the ICSP Subcommittee on the Taxonomy of Brucella, they represent a novel species within the genus Brucella, for which the name Brucella papionis sp. nov. is proposed, with the type strain F8/08-60(T) (?=?NCTC 13660(T)?=?CIRMBP 0958(T)).

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Omp2b Porin Alteration in the Course of Evolution of Brucella spp.

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Omp2b Porin Alteration in the Course of Evolution of <i>Brucella</i> spp.

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