Brucella microti: the genome sequence of an emerging pathogen

<p>Abstract</p> <p>Background</p> <p>Using a combination of pyrosequencing and conventional Sanger sequencing, the complete genome sequence of the recently described novel <it>Brucella </it>species, <it>Brucella microti</it>, was determined. <it>B. microti </it>is a member of the genus <it>Brucella </it>within the <it>Alphaproteobacteria</it>, which consists of medically important highly pathogenic facultative intracellular bacteria. In contrast to all other <it>Brucella </it>species, <it>B. microti </it>is a fast growing and biochemically very active microorganism with a phenotype more similar to that of <it>Ochrobactrum</it>, a facultative human pathogen. The atypical phenotype of <it>B. microti </it>prompted us to look for genomic differences compared to other <it>Brucella </it>species and to look for similarities with <it>Ochrobactrum</it>.</p> <p>Results</p> <p>The genome is composed of two circular chromosomes of 2,117,050 and 1,220,319 base pairs. Unexpectedly, we found that the genome sequence of <it>B. microti </it>is almost identical to that of <it>Brucella suis </it>1330 with an overall sequence identity of 99.84% in aligned regions. The most significant structural difference between the two genomes is a bacteriophage-related 11,742 base pairs insert only present in <it>B. microti</it>. However, this insert is unlikely to have any phenotypical consequence. Only four protein coding genes are shared between <it>B. microti </it>and <it>Ochrobactrum anthropi </it>but impaired in other sequenced <it>Brucella</it>. The most noticeable difference between <it>B. microti </it>and other <it>Brucella </it>species was found in the sequence of the 23S ribosomal RNA gene. This unusual variation could have pleiotropic effects and explain the fast growth of <it>B. microti</it>.</p> <p>Conclusion</p> <p>Contrary to expectations from the phenotypic analysis, the genome sequence of <it>B. microti </it>is highly similar to that of known <it>Brucella </it>species, and is remotely related to the one of <it>O. anthropi</it>. How the few differences in gene content between <it>B. microti </it>and <it>B. suis </it>1330 could result in vastly different phenotypes remains to be elucidated. This unexpected finding will complicate the task of identifying virulence determinants in the <it>Brucella </it>genus. The genome sequence of <it>B. microti </it>will serve as a model for differential expression analysis and complementation studies. Our results also raise some concerns about the importance given to phenotypical traits in the definition of bacterial species.</p

The genome sequence of Brucella pinnipedialis B2/94 sheds light on the evolutionary history of the genus Brucella

International audienceBackground: Since the discovery of the Malta fever agent, Brucella melitensis, in the 19th century, six terrestrial mammal-associated Brucella species were recognized over the next century. More recently the number of novel Brucella species has increased and among them, isolation of species B. pinnipedialis and B. ceti from marine mammals raised many questions about their origin as well as on the evolutionary history of the whole genus. Results: We report here on the first complete genome sequence of a Brucella strain isolated from marine mammals, Brucella pinnipedialis strain B2/94. A whole gene-based phylogenetic analysis shows that five main groups of host-associated Brucella species rapidly diverged from a likely free-living ancestor close to the recently isolated B. microti. However, this tree lacks the resolution required to resolve the order of divergence of those groups. Comparative analyses focusing on a) genome segments unshared between B. microti and B. pinnipedialis, b) gene deletion/fusion events and c) positions and numbers of Brucella specific IS711 elements in the available Brucella genomes provided enough information to propose a branching order for those five groups. Conclusions: In this study, it appears that the closest relatives of marine mammal Brucella sp. are B. ovis and Brucella sp. NVSL 07-0026 isolated from a baboon, followed by B. melitensis and B. abortus strains, and finally the group consisting of B. suis strains, including B. canis and the group consisting of the single B. neotomae species. We were not able, however, to resolve the order of divergence of the two latter groups

Mimivirus and the emerging concept of "giant" virus

The recently discovered Acanthamoeba polyphaga Mimivirus is the largest known DNA virus. Its particle size (>400 nm), genome length (1.2 million bp) and large gene repertoire (911 protein coding genes) blur the established boundaries between viruses and parasitic cellular organisms. In addition, the analysis of its genome sequence identified new types of genes not expected to be seen in a virus, such as aminoacyl-tRNA synthetases and other central components of the translation machinery. In this article, we examine how the finding of a giant virus for the first time overlapping with the world of cellular organisms in terms of size and genome complexity might durably influence the way we look at microbial biodiversity, and force us to fundamentally revise our classification of life forms. We propose to introduce the word "girus" to recognize the intermediate status of these giant DNA viruses, the genome complexity of which make them closer to small parasitic prokaryotes than to regular viruses.Comment: Submitted to Virus Researc

PROTOGENE: turning amino acid alignments into bona fide CDS nucleotide alignments

We describe Protogene, a server that can turn a protein multiple sequence alignment into the equivalent alignment of the original gene coding DNA. Protogene relies on a pipeline where every initial protein sequence is BLASTed against RefSeq or NR. The annotation associated with potential matches is used to identify the gene sequence. This gene sequence is then aligned with the query protein using Exonerate in order to extract a coding nucleotide sequence matching the original protein. Protogene can handle protein fragments and will return every CDS coding for a given protein, even if they occur in different genomes. Protogene is available from

Expresso: automatic incorporation of structural information in multiple sequence alignments using 3D-Coffee

Expresso is a multiple sequence alignment server that aligns sequences using structural information. The user only needs to provide sequences. The server runs BLAST to identify close homologues of the sequences within the PDB database. These PDB structures are used as templates to guide the alignment of the original sequences using structure-based sequence alignment methods like SAP or Fugue. The final result is a multiple sequence alignment of the original sequences based on the structural information of the templates. An advanced mode makes it possible to either upload private structures or specify which PDB templates should be used to model each sequence. Providing the suitable structural information is available, Expresso delivers sequence alignments with accuracy comparable with structure-based alignments. The server is available on http://www.tcoffee.or

Expresso: automatic incorporation of structural information in multiple sequence alignments using 3D-Coffee

Expresso is a multiple sequence alignment server that aligns sequences using structural information. The user only needs to provide sequences. The server runs BLAST to identify close homologues of the sequences within the PDB database. These PDB structures are used as templates to guide the alignment of the original sequences using structure-based sequence alignment methods like SAP or Fugue. The final result is a multiple sequence alignment of the original sequences based on the structural information of the templates. An advanced mode makes it possible to either upload private structures or specify which PDB templates should be used to model each sequence. Providing the suitable structural information is available, Expresso delivers sequence alignments with accuracy comparable with structure-based alignments. The server is available on

Testing ecological theories with sequence similarity networks: marine ciliates exhibit similar geographic dispersal patterns as multicellular organisms

International audienceBackground : High-throughput sequencing technologies are lifting major limitations to molecular-based ecological studies of eukaryotic microbial diversity, but analyses of the resulting millions of short sequences remain a major bottleneck for these approaches. Here, we introduce the analytical and statistical framework of sequence similarity networks, increasingly used in evolutionary studies and graph theory, into the field of ecology to analyze novel pyrosequenced V4 small subunit rDNA (SSU-rDNA) sequence data sets in the context of previous studies, including SSU-rDNA Sanger sequence data from cultured ciliates and from previous environmental diversity inventories.Results : Our broadly applicable protocol quantified the progress in the description of genetic diversity of ciliates by environmental SSU-rDNA surveys, detected a fundamental historical bias in the tendency to recover already known groups in these surveys, and revealed substantial amounts of hidden microbial diversity. Moreover, network measures demonstrated that ciliates are not globally dispersed, but are structured by habitat and geographical location at intermediate geographical scale, as observed for bacteria, plants, and animals.Conclusions : Currently available ‘universal’ primers used for local in-depth sequencing surveys provide little hope to exhaust the significantly higher ciliate (and most likely microbial) diversity than previously thought. Network analyses such as presented in this study offer a promising way to guide the design of novel primers and to further explore this vast and structured microbial diversity

Reductive Genome Evolution from the Mother of Rickettsia

The Rickettsia genus is a group of obligate intracellular α-proteobacteria representing a paradigm of reductive evolution. Here, we investigate the evolutionary processes that shaped the genomes of the genus. The reconstruction of ancestral genomes indicates that their last common ancestor contained more genes, but already possessed most traits associated with cellular parasitism. The differences in gene repertoires across modern Rickettsia are mainly the result of differential gene losses from the ancestor. We demonstrate using computer simulation that the propensity of loss was variable across genes during this process. We also analyzed the ratio of nonsynonymous to synonymous changes (Ka/Ks) calculated as an average over large sets of genes to assay the strength of selection acting on the genomes of Rickettsia, Anaplasmataceae, and free-living γ-proteobacteria. As a general trend, Ka/Ks were found to decrease with increasing divergence between genomes. The high Ka/Ks for closely related genomes are probably due to a lag in the removal of slightly deleterious nonsynonymous mutations by natural selection. Interestingly, we also observed a decrease of the rate of gene loss with increasing divergence, suggesting a similar lag in the removal of slightly deleterious pseudogene alleles. For larger divergence (Ks > 0.2), Ka/Ks converge toward similar values indicating that the levels of selection are roughly equivalent between intracellular α-proteobacteria and their free-living relatives. This contrasts with the view that obligate endocellular microorganisms tend to evolve faster as a consequence of reduced effectiveness of selection, and suggests a major role of enhanced background mutation rates on the fast protein divergence in the obligate intracellular α-proteobacteria

Genome Analysis of Minibacterium massiliensis Highlights the Convergent Evolution of Water-Living Bacteria

Filtration usually eliminates water-living bacteria. Here, we report on the complete genome sequence of Minibacterium massiliensis, a β-proteobacteria that was recovered from 0.22-μm filtered water used for patients in the hospital. The unexpectedly large 4,110,251-nucleotide genome sequence of M. massiliensis was determined using the traditional shotgun sequencing approach. Bioinformatic analyses shows that the M. massiliensis genome sequence illustrates characteristic features of water-living bacteria, including overrepresentation of genes encoding transporters and transcription regulators. Phylogenomic analysis based on the gene content of available bacterial genome sequences displays a congruent evolution of water-living bacteria from various taxonomic origins, principally for genes involved in energy production and conversion, cell division, chromosome partitioning, and lipid metabolism. This phylogenomic clustering partially results from lateral gene transfer, which appears to be more frequent in water than in other environments. The M. massiliensis genome analyses strongly suggest that water-living bacteria are a common source for genes involved in heavy-metal resistance, antibiotics resistance, and virulence factors