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Rickettsiae are obligate intracellular bacteria that can cause mild to life-threatening diseases, including epidemic typhus, one of the oldest pernicious diseases of mankind. Clinical awareness of rickettsial diseases and molecular diagnosis have shown that rickettsioses should be viewed as new emerging and reemerging diseases. Rickettsia has been shown to be a large genus with a worldwide distribution, a very diverse host range, including hosts that have no relationship with vertebrate. Genomic studies have demonstrated genome reduction due to gene loss associated with increased pathogenicity and horizontal DNA acquisition according to a sympatric mode of evolution in hosts that contain several organisms. This article presents a review of genotyping techniques and examines the principle of genotype determination in terms of taxonomic strategies and detection methods. This article summarizes the epidemiological and pathological features of Rickettsia and discusses the genomic findings that help the understanding of the evolution of pathogenicity including the deleterious mutations of repair systems and the toxin-antitoxin systems.

Background Horizontal transfer plays an important role in the evolution of bacterial genomes, yet it obeys several constraints, including the ecological opportunity to meet other organisms, the presence of transfer systems, and the fitness of the transferred genes. Bacteria from the Planctomyctetes, Verrumicrobia, Chlamydiae (PVC) super-phylum have a compartmentalized cell plan delimited by an intracytoplasmic membrane that might constitute an additional constraint with particular impact on bacterial evolution. In this investigation, we studied the evolution of 33 genomes from PVC species and focused on the rate and the nature of horizontally transferred sequences in relation to their habitat and their cell plan. Results Using a comparative phylogenomic approach, we showed that habitat influences the evolution of the bacterial genome’s content and the flux of horizontal transfer of DNA (HT). Thus bacteria from soil, from insects and ubiquitous bacteria presented the highest average of horizontal transfer compared to bacteria living in water, extracellular bacteria in vertebrates, bacteria from amoeba and intracellular bacteria in vertebrates (with a mean of 379 versus 110 events per species, respectively and 7.6% of each genomes due to HT against 4.8%). The partners of these transfers were mainly bacterial organisms (94.9%); they allowed us to differentiate environmental bacteria, which exchanged more with Proteobacteria, and bacteria from vertebrates, which exchanged more with Firmicutes. The functional analysis of the horizontal transfers revealed a convergent evolution, with an over-representation of genes encoding for membrane biogenesis and lipid metabolism, among compartmentalized bacteria in the different habitats. Conclusions The presence of an intracytoplasmic membrane in PVC species seems to affect the genome’s evolution through the selection of transferred DNA, according to their encoded functions. Electronic supplementary material The online version of this article (doi:10.1186/s12862-017-0921-3) contains supplementary material, which is available to authorized users.

It is well known that horizontal gene transfer (HGT) is a major force in the evolution of prokaryotes. During the adaptation of a bacterial population to a new ecological niche, and particularly for intracellular bacteria, selective pressures are shifted and ecological niches reduced, resulting in a lower rate of genetic connectivity. HGT and positive selection are therefore two important evolutionary forces in microbial pathogens that drive adaptation to new hosts. In this study, we use genomic distance analyses, phylogenomic networks, tree topology comparisons, and Bayesian inference methods to investigate to what extent HGT has occurred during the evolution of the genus Rickettsia, the effect of the use of different genomic regions in estimating reticulate evolution and HGT events, and the link of these to host range. We show that ecological specialization restricts recombination occurrence in Rickettsia, but other evolutionary processes and genome architecture are also important for the occurrence of HGT. We found that recombination, genomic rearrangements, and genome conservation all show evidence of network-like evolution at whole-genome scale. We show that reticulation occurred mainly, but not only, during the early Rickettsia radiation, and that core proteome genes of every major functional category have experienced reticulated evolution and possibly HGT. Overall, the evolution of Rickettsia bacteria has been tree-like, with evidence of HGT and reticulated evolution for around 10–25% of the core Rickettsia genome. We present evidence of extensive recombination/incomplete lineage sorting (ILS) during the radiation of the genus, probably linked with the emergence of intracellularity in a wide range of hosts.

The order Rickettsiales comprises obligate intracellular bacteria that are the ancestors of modern eukaryotes. These bacteria infect various vectors and hosts, with some species being pathogenic to man. Rickettsiales have small, degraded genomes and provide a paradigm for increased pathogenicity despite gene loss; significant levels of genetic exchange occur between bacteria that infect the same host and with the eukaryotic hosts themselves. Crosstalk between host and bacteria appears to be mediated by a Type IV secretion system and proteins containing eukaryotic-like repeat motifs. Rickettsiales also manipulate host reproduction and induce host resistance to viruses. Manipulation of its host by Rickettsiales has long been misunderstood because of technical difficulties, but recent advances in understanding bacterial–eukaryotes interactions have been made and are reviewed here.

International audience; The intracellular flea symbiont, Rickettsia felis, may meet other organisms intracellularly such as R. typhi. We used a single-gene phylogenetic approach of the 1375 R. felis genes to look for horizontal transfers that occurred as a result of the bacterial promiscuity with other organisms. Our results showed that besides genes that are linked to the Spotted Fever Group, 165 genes have a different history and are linked to other Rickettsia such as R. bellii (107 genes), R. typhi (15 genes), or to other bacteria such as Legionella sp. and Francisella sp. or to eukaryotes. Among these genes, we identified 73 individual genes and 34 spatial clusters containing 2–4 adjacent genes, a total of 79 genes, with evidence of en bloc transfer. We described 13 chimeric genes resulting from gene recombination with sympatric R. typhi. The transferred DNA sequences present different sizes and functions, suggesting that the horizontal transfer in R. felis is random and neutral within its specific host. Our study shows that the strict intracellular bacteria R. felis exhibits a mosaic genome. We therefore developed a new representation for the evolutionary history of R. felis showing its different putative ancestors in the form of a rhizome.

Many of the definitions in microbiology are currently false. We have reviewed the great denominations of microbiology and attempted to free microorganisms from the theories of the twentieth century. The presence of compartmentation and a nucleoid in Planctomycetes clearly calls into question the accuracy of the definitions of eukaryotes and prokaryotes. Archaea are viewed as prokaryotes resembling bacteria. However, the name archaea, suggesting an archaic origin of lifestyle, is inconsistent with the lifestyle of this family. Viruses are defined as small, filterable infectious agents, but giant viruses challenge the size criteria used for the definition of a virus. Pathogenicity does not require the acquisition of virulence factors (except for toxins), and in many cases, gene loss is significantly inked to the emergence of virulence. Species classification based on 16S rRNA is useless for taxonomic purposes of human pathogens, as a 2% divergence would classify all Rickettsiae within the same species and would not identify bacteria specialized for mammal infection. The use of metagenomics helps us to understand evolution and physiology by elucidating the structure, function, and interactions of the major microbial communities, but it neglects the minority populations. Finally, Darwin's descent with modification theory, as represented by the tree of life, no longer matches our current genomic knowledge because genomics has revealed the occurrence of de novo-created genes and the mosaic structure of genomes, the Rhizome of life is therefore more appropriate.

Gram-positive, facultatively anaerobic, rod-shaped bacteria were isolated from the blood of a patient with endocarditis (strain 5401744T) and from the hip joint fluid of a patient with an infected orthopaedic prosthesis (strain 5402485T). These strains were characterized by using a polyphasic taxonomic approach. Based on cellular morphology and biochemical criteria the two isolates were tentatively assigned to the genus Corynebacterium, although they did not correspond to any recognized species. The predominant fatty acids were a mix of C18:2omega6,9c and anteiso-C18:0 (32.1% of the total), C16:0 (26.3%) and C18:1omega9c (22.5%) for strain 5402485T and C18:1omega9c (36.4%), C17:1omega9c (27.1%) and C16:0 (10.9%) for strain 5401744T. Phylogenetic analysis based on 16S rRNA gene sequence comparisons showed that strain 5401744T was closely related to the type strains of Corynebacterium auris, Corynebacterium capitovis, Corynebacterium lipophiloflavum and Corynebacterium mycetoides (97.0, 96.6, 96.5 and 96.3% similarity, respectively) and strain 5402485T was closely related to the type strains of Corynebacterium macginleyi, Corynebacterium accolens, Corynebacterium tuberculostearicum, Corynebacterium confusum, Corynebacterium mastitidis and Corynebacterium renale (95.6, 95.3, 95.3, 94.5, 94.0 and 93.5%, respectively). On the basis of phenotypic data and phylogenetic inference, these isolates are considered to represent two novel species of the genus Corynebacterium, for which the names Corynebacterium timonense sp. nov. (type strain, 5401744T=CSUR P20T=CIP 109424T=CCUG 53856T) and Corynebacterium massiliense sp. nov. (type strain, 5402485T=CSUR P19T=CIP 109423T=CCUG 53857T) are proposed.

Background Genome size and gene content in bacteria are associated with their lifestyles. Obligate intracellular bacteria (i.e., mutualists and parasites) have small genomes that derived from larger free-living bacterial ancestors; however, the different steps of bacterial specialization from free-living to intracellular lifestyle have not been studied comprehensively. The growing number of available sequenced genomes makes it possible to perform a statistical comparative analysis of 317 genomes from bacteria with different lifestyles. Results Compared to free-living bacteria, host-dependent bacteria exhibit fewer rRNA genes, more split rRNA operons and fewer transcriptional regulators, linked to slower growth rates. We found a function-dependent and non-random loss of the same 100 orthologous genes in all obligate intracellular bacteria. Thus, we showed that obligate intracellular bacteria from different phyla are converging according to their lifestyle. Their specialization is an irreversible phenomenon characterized by translation modification and massive gene loss, including the loss of transcriptional regulators. Although both mutualists and parasites converge by genome reduction, these obligate intracellular bacteria have lost distinct sets of genes in the context of their specific host associations: mutualists have significantly more genes that enable nutrient provisioning whereas parasites have genes that encode Types II, IV, and VI secretion pathways. Conclusion Our findings suggest that gene loss, rather than acquisition of virulence factors, has been a driving force in the adaptation of parasites to eukaryotic cells. This comparative genomic analysis helps to explore the strategies by which obligate intracellular genomes specialize to particular host-associations and contributes to advance our knowledge about the mechanisms of bacterial evolution. Reviewers This article was reviewed by Eugene V. Koonin, Nicolas Galtier, and Jeremy Selengut.

Rickettsiae are obligate intracellular bacteria associated with arthropods, often pathogenic for humans. The Rickettsia genus belongs to the Alphaproteobacteria; it was divided into three major subgroups, mainly on the basis of phenotypic and serological features: the typhus group (TG), made of Rickettsia prowazekii and R. typhi, the spotted fever group (SFG) including R. conorii, R. africae, R. massiliae, R. akari, R. felis and several other validated species, and a group of marginal and divergent species including R. bellii and R. canadensis. Rickettsia spp. express few remarkable phenotypic characteristics. Therefore, their precise identification and phylogenetic classification have mainly relied on the analysis of molecular sequences. Phylogenetic analysis based on 16S rDNA gene sequences has frequently been

Bartonella rattimassiliensis is a facultative intracellular bacterium isolated from the blood of Rattus norvegicus in Marseille. The present study reports the draft genome of B. rattimassiliensis strain 15908 (CIP 107705 T ).

Bartonella rattaustraliani is a facultative intracellular bacterium isolated from the blood of a Rattus sp. in Australia. The present study reports the draft genome of B. rattaustraliani strain AUST/NH4 (CSUR B609 T ).

BACKGROUND: Human head lice and body lice have been classified based on phenotypic characteristics, including geographical source, ecotype (preferred egg laying site hair or clothes), shape and color. More recently, genotypic studies have been based on mitochondrial genes, nuclear genes and intergenic spacers. Mitochondrial genetic analysis reclassified lice into three genotypes (A, B and C). However, no previous study has attempted to correlate both genotypic and phenotypic data. MATERIALS AND METHODS: Lice were collected in four African countries: Senegal, Burundi, Rwanda and Ethiopia and were photographed to compare their colors. The Multi-Spacer-Typing (MST) method was used to genotype lice belonging to the worldwide Clade A, allowing a comparison of phenotypic and genotypic data. RESULTS: No congruence between louse color and genotype has been identified. Phylogenetic analysis of the spacer PM2, performed including lice from other sources, showed the existence of an African cluster of human lice. However, the analysis of other spacers suggested that lice from different areas are interbreeding. CONCLUSIONS: We identified two geotypes of Clade A head and body lice including one that is specifically African, that can be either black or grey and can live on the head or in clothing. We also hypothesized that lice from different areas are interbreeding.