Comparison Of Gene Content Research Articles

Comparative Genomic Analysis Reveals Gene Content Diversity, Phylogenomic Contour, Putative Virulence Determinants, and Potential Diagnostic Markers within Pythium insidiosum Traits

Pythium insidiosum has successfully evolved into a human/animal filamentous pathogen, causing pythiosis, a life-threatening disease, worldwide. The specific rDNA-based genotype of P. insidiosum (clade I, II, or III) is associated with the different hosts and disease prevalence. Genome evolution of P. insidiosum can be driven by point mutations, pass vertically to the offspring, and diverge into distinct lineages, leading to different virulence, including the ability to be unrecognized by the host. We conducted comprehensive genomic comparisons of 10 P. insidiosum strains and 5 related Pythium species using our online "Gene Table" software to investigate the pathogen's evolutionary history and pathogenicity. In total, 245,378 genes were found in all 15 genomes and grouped into 45,801 homologous gene clusters. Gene contents among P. insidiosum strains varied by as much as 23%. Our results showed a strong agreement between the phylogenetic analysis of 166 core genes (88,017 bp) identified across all genomes and the hierarchical clustering analysis of gene presence/absence profiles, suggesting divergence of P. insidiosum into two groups, clade I/II and clade III strains, and the subsequent segregation of clade I and clade II. A stringent gene content comparison using the Pythium Gene Table provided 3263 core genes exclusively presented in all P. insidiosum strains but no other Pythium species, which could involve host-specific pathogenesis and serve as biomarkers for diagnostic purposes. More studies focusing on characterizing the biological function of the core genes (including the just-identified putative virulence genes encoding hemagglutinin/adhesin and reticulocyte-binding protein) are needed to explore the biology and pathogenicity of this pathogen.

Comparative analysis reveals distinctive genomic features of Taiwan hot-spring cyanobacterium Thermosynechococcus sp. TA-1.

Thermosynechococcus is a genus of thermophilic unicellular cyanobacteria that dominates microbial mats in Asian non-acidic hot springs. These cyanobacteria are the major primary producers in their ecological niches and are promising sources of thermostable enzymes for biotechnology applications. To improve our understanding of these organisms, we conducted whole-genome sequencing of a novel strain for comparative analysis with other representatives in the same genus. This newly characterized strain, Thermosynechococcus sp. TA-1, was isolated from the Taian hot springs in Taiwan. Analyses based on average nucleotide identity (ANI) and genome-scale phylogeny suggested that TA-1 and another Taiwanese strain CL-1 belong to a novel species-level taxon. Two metagenome-assembled genomes (MAGs) originated from India represent the sister group, and Thermosynechococcus elongatus PKUAC-SCTE542 from China is the next closest lineage. All cultivated strains and MAGs from Japan form a separate monophyletic clade and could be classified into two species-level taxa. Intriguingly, although TA-1 and CL-1 share 97.0% ANI, the genome alignment identified at least 16 synteny breakpoints that are mostly associated with transposase genes, which illustrates the dynamic nature of their chromosomal evolution. Gene content comparisons identified multiple features distinct at species- or strain-level among these Thermosynechococcus representatives. Examples include genes involved in bicarbonate transportation, nitric oxide protection, urea utilization, kanamycin resistance, restriction-modification system, and chemotaxis. Moreover, we observed the insertion of type II inteins in multiple genes of the two Taiwanese strains and inferred putative horizontal transfer of an asparagine synthase gene (asnB) associated with exopolysaccharides gene cluster. Taken together, while previous work suggested that strains in this genus share a highly conserved genomic core and no clear genetic differentiation could be linked to environmental factors, we found that the overall pattern of gene content divergence is largely congruent with core genome phylogeny. However, it is difficult to distinguish between the roles of phylogenetic relatedness and geographic proximity in shaping the genetic differentiation. In conclusion, knowledge of the genomic differentiation among these strains provides valuable resources for future functional characterization.

Comparative genomics reveals broad genetic diversity, extensive recombination and nascent ecological adaptation in Micrococcus luteus

BackgroundMicrococcus luteus is a group of actinobacteria that is widely used in biotechnology and is being thought as an emerging nosocomial pathogen. With one of the smallest genomes of free-living actinobacteria, it is found in a wide range of environments, but intraspecies genetic diversity and adaptation strategies to various environments remain unclear. Here, comparative genomics, phylogenomics, and genome-wide association studies were used to investigate the genomic diversity, evolutionary history, and the potential ecological differentiation of the species.ResultsHigh-quality genomes of 66 M. luteus strains were downloaded from the NCBI GenBank database and core and pan-genome analysis revealed a considerable intraspecies heterogeneity. Phylogenomic analysis, gene content comparison, and average nucleotide identity calculation consistently indicated that the species has diverged into three well-differentiated clades. Population structure analysis further suggested the existence of an unknown ancestor or the fourth, yet unsampled, clade. Reconstruction of gene gain/loss events along the evolutionary history revealed both early events that contributed to the inter-clade divergence and recent events leading to the intra-clade diversity. We also found convincing evidence that recombination has played a key role in the evolutionary process of the species, with upto two-thirds of the core genes having been affected by recombination. Furthermore, distribution of mammal-associated strains (including pathogens) on the phylogenetic tree suggested that the last common ancestor had a free-living lifestyle, and a few recently diverged lineages have developed a mammal-associated lifestyle separately. Consistently, genome-wide association analysis revealed that mammal-associated strains from different lineages shared genes functionally relevant to the host-associated lifestyle, indicating a recent ecological adaption to the new host-associated habitats.ConclusionsThese results revealed high intraspecies genomic diversity of M. luteus and highlighted that gene gain/loss events and extensive recombination events played key roles in the genome evolution. Our study also indicated that, as a free-living species, some lineages have recently developed or are developing a mammal-associated lifestyle. This study provides insights into the mechanisms that drive the genome evolution and adaption to various environments of a bacterial species.

Sequence of a Coxiella Endosymbiont of the Tick Amblyomma nuttalli Suggests a Pattern of Convergent Genome Reduction in the Coxiella Genus.

Ticks require bacterial symbionts for the provision of necessary compounds that are absent in their hematophagous diet. Such symbionts are frequently vertically transmitted and, most commonly, belong to the Coxiella genus, which also includes the human pathogen Coxiella burnetii. This genus can be divided in four main clades, presenting partial but incomplete cocladogenesis with the tick hosts. Here, we report the genome sequence of a novel Coxiella, endosymbiont of the African tick Amblyomma nuttalli, and the ensuing comparative analyses. Its size (∼1 Mb) is intermediate between symbionts of Rhipicephalus species and other Amblyomma species. Phylogenetic analyses show that the novel sequence is the first genome of the B clade, the only one for which no genomes were previously available. Accordingly, it allows to draw an enhanced scenario of the evolution of the genus, one of parallel genome reduction of different endosymbiont lineages, which are now at different stages of reduction from a more versatile ancestor. Gene content comparison allows to infer that the ancestor could be reminiscent of C. burnetii. Interestingly, the convergent loss of mismatch repair could have been a major driver of such reductive evolution. Predicted metabolic profiles are rather homogenous among Coxiella endosymbionts, in particular vitamin biosynthesis, consistently with a host-supportive role. Concurrently, similarities among Coxiella endosymbionts according to host genus and despite phylogenetic unrelatedness hint at possible host-dependent effects.

Evolutionary Mechanisms of Long-Term Genome Diversification Associated With Niche Partitioning in Marine Picocyanobacteria.

Marine picocyanobacteria of the genera Prochlorococcus and Synechococcus are the most abundant photosynthetic organisms on Earth, an ecological success thought to be linked to the differential partitioning of distinct ecotypes into specific ecological niches. However, the underlying processes that governed the diversification of these microorganisms and the appearance of niche-related phenotypic traits are just starting to be elucidated. Here, by comparing 81 genomes, including 34 new Synechococcus, we explored the evolutionary processes that shaped the genomic diversity of picocyanobacteria. Time-calibration of a core-protein tree showed that gene gain/loss occurred at an unexpectedly low rate between the different lineages, with for instance 5.6 genes gained per million years (My) for the major Synechococcus lineage (sub-cluster 5.1), among which only 0.71/My have been fixed in the long term. Gene content comparisons revealed a number of candidates involved in nutrient adaptation, a large proportion of which are located in genomic islands shared between either closely or more distantly related strains, as identified using an original network construction approach. Interestingly, strains representative of the different ecotypes co-occurring in phosphorus-depleted waters (Synechococcus clades III, WPC1, and sub-cluster 5.3) were shown to display different adaptation strategies to this limitation. In contrast, we found few genes potentially involved in adaptation to temperature when comparing cold and warm thermotypes. Indeed, comparison of core protein sequences highlighted variants specific to cold thermotypes, notably involved in carotenoid biosynthesis and the oxidative stress response, revealing that long-term adaptation to thermal niches relies on amino acid substitutions rather than on gene content variation. Altogether, this study not only deciphers the respective roles of gene gains/losses and sequence variation but also uncovers numerous gene candidates likely involved in niche partitioning of two key members of the marine phytoplankton.

Genome comparisons suggest an association between Ceratocystis host adaptations and effector clusters in unique transposable element families

Ceratocystis fimbriata is a host specific fungal pathogen of sweet potato (Ipomoea batatas). The closely related species, C. manginecans, is an important pathogen of trees (e.g. Acacia mangium and Mangifera indica) but has never been isolated from tuber crops. The genetic factors that determine the host range and host specificity of these species have not been determined. The aim of this study was to compare the genomes of C. fimbriata and C. manginecans in order to identify species-specific genetic differences that could be associated with host specificity. This included whole-genome alignments as well as comparisons of gene content and transposable elements (TEs). The genomes of the two species were found to be very similar, sharing similar catalogues of CAZymes, peptidases and lipases. However, the genomes of the two species also varied, harbouring species-specific genes (e.g. small secreted effectors, nutrient processing proteins and stress response proteins). A portion of the TEs identified (17%) had a unique distribution in each species. Transposable elements appeared to have played a prominent role in the divergence of the two species because they were strongly associated with chromosomal translocations and inversions as well as with unique genomic regions containing species-specific genes. Two large effector clusters, with unique TEs in each species, were identified. These effectors displayed non-synonymous mutations and deletions, conserved within a species, and could serve as mutational hot-spots for the development of host specificity in the two species.

Genomic Acquisitions in Emerging Populations ofXanthomonas vasicolapv.vasculorumInfecting Corn in the United States and Argentina

Xanthomonas vasicola pv. vasculorum is an emerging bacterial plant pathogen that causes bacterial leaf streak on corn. First described in South Africa in 1949, reports of this pathogen have greatly increased in the past years in South America and in the United States. The rapid spread of this disease in North and South America may be due to more favorable environmental conditions, susceptible hosts and/or genomic changes that favored the spread. To understand whether genetic mechanisms exist behind the recent spread of X. vasicola pv. vasculorum, we used comparative genomics to identify gene acquisitions in X. vasicola pv. vasculorum genomes from the United States and Argentina. We sequenced 41 genomes of X. vasicola pv. vasculorum and the related sorghum-infecting X. vasicola pv. holcicola and performed comparative analyses against all available X. vasicola genomes. Time-measured phylogenetic analyses showed that X. vasicola pv. vasculorum strains from the United States and Argentina are closely related and arose from two introductions to North and South America. Gene content comparisons identified clusters of genes enriched in corn X. vasicola pv. vasculorum that showed evidence of horizontal transfer including one cluster corresponding to a prophage found in all X. vasicola pv. vasculorum strains from the United States and Argentina as well as in X. vasicola pv. holcicola strains. In this work, we explore the genomes of an emerging phytopathogen population as a first step toward identifying genetic changes associated with the emergence. The acquisitions identified may contain virulence determinants or other factors associated with the spread of X. vasicola pv. vasculorum in North and South America and will be the subject of future work.

Gene Composition as a Potential Barrier to Large Recombinations in the Bacterial Pathogen Klebsiella pneumoniae.

Klebsiella pneumoniae (Kp) is one of the most important nosocomial pathogens worldwide, able to cause multiorgan infections and hospital outbreaks. One of the most widely disseminated lineage of Kp is the clonal group 258 (CG258), which includes the highly resistant “high-risk” sequence types ST258 and ST11. Genomic investigations revealed that very large recombination events have occurred during the emergence of Kp lineages. A striking example is provided by ST258, which has undergone a recombination event that replaced over 1 Mb of the genome with DNA from an unrelated Kp donor. Although several examples of this phenomenon have been documented in Kp and other bacterial species, the significance of these very large recombination events for the emergence of either hypervirulent or resistant clones remains unclear. Here, we present an analysis of 834 Kp genomes that provides data on the frequency of these very large recombination events (defined as those involving >100 kb), their distribution within the genome, and the dynamics of gene flow within the Kp population. We note that very large recombination events occur frequently, and in multiple lineages, and that the majority of recombinational exchanges are clustered within two overlapping genomic regions, which have been involved by recombination events with different frequencies. Our results also indicate that certain lineages are more likely to act as donors to CG258. Furthermore, comparison of gene content in CG258 and non-CG258 strains agrees with this pattern, suggesting that the success of a large recombination depends on gene composition in the exchanged genomic portion.

Genome analysis-based union of the genus Mesoplasma with the genus Entomoplasma.

Early characterization of strains designated into the genera Entomoplasma and Mesoplasma was based upon biological and chemical characteristics. With the advent of 16S rRNA gene sequence analysis as an added taxonomic character, it became clear that the two genera did not form distinct and separate monophyletic clusters. A genome-level analysis of all 17 validly published species within the family Entomoplasmataceae has recently been performed. Phylogenetic analyses, comparisons of gene content, and the lack of genus-specific genes supported that species from the two genera are intermixed and should not be taxonomically separated. This level of analysis clearly reveals the necessity to revise the taxonomy of this family by merging the two genera into one, Entomoplasma. Additionally, it was definitively determined that the strain originally designated as Acholeplasma multilocale resides in this cluster and should be formally renamed as Entomoplasma multilocale. Merging Mesoplasma and Entomoplasma yields a paraphyletic genus, but is supported by cell morphology and ecology to be distinguished from the genera Spiroplasma and Mycoplasma.

Comparative transcriptomic analyses and single-cell RNA sequencing of the freshwater planarian Schmidtea mediterranea identify major cell types and pathway conservation

BackgroundIn the Lophotrochozoa/Spiralia superphylum, few organisms have as high a capacity for rapid testing of gene function and single-cell transcriptomics as the freshwater planaria. The species Schmidtea mediterranea in particular has become a powerful model to use in studying adult stem cell biology and mechanisms of regeneration. Despite this, systematic attempts to define gene complements and their annotations are lacking, restricting comparative analyses that detail the conservation of biochemical pathways and identify lineage-specific innovations.ResultsIn this study we compare several transcriptomes and define a robust set of 35,232 transcripts. From this, we perform systematic functional annotations and undertake a genome-scale metabolic reconstruction for S. mediterranea. Cross-species comparisons of gene content identify conserved, lineage-specific, and expanded gene families, which may contribute to the regenerative properties of planarians. In particular, we find that the TRAF gene family has been greatly expanded in planarians. We further provide a single-cell RNA sequencing analysis of 2000 cells, revealing both known and novel cell types defined by unique signatures of gene expression. Among these are a novel mesenchymal cell population as well as a cell type involved in eye regeneration. Integration of our metabolic reconstruction further reveals the extent to which given cell types have adapted energy and nucleotide biosynthetic pathways to support their specialized roles.ConclusionsIn general, S. mediterranea displays a high level of gene and pathway conservation compared with other model systems, rendering it a viable model to study the roles of these pathways in stem cell biology and regeneration.

Genomic Characterization and Copy Number Variation of Bacillus anthracis Plasmids pXO1 and pXO2 in a Historical Collection of 412 Strains.

Bacillus anthracis plasmids pXO1 and pXO2 carry the main virulence factors responsible for anthrax. However, the extent of copy number variation within the species and how the plasmids are related to pXO1/pXO2-like plasmids in other species of the Bacillus cereus sensu lato group remain unclear. To gain new insights into these issues, we sequenced 412 B.anthracis strains representing the total phylogenetic and ecological diversity of the species. Our results revealed that B.anthracis genomes carried, on average, 3.86 and 2.29 copies of pXO1 and pXO2, respectively, and also revealed a positive linear correlation between the copy numbers of pXO1 and pXO2. No correlation between the plasmid copy number and the phylogenetic relatedness of the strains was observed. However, genomes of strains isolated from animal tissues generally maintained a higher plasmid copy number than genomes of strains from environmental sources (P < 0.05 [Welch two-sample ttest]). Comparisons against B.cereus genomes carrying complete or partial pXO1-like and pXO2-like plasmids showed that the plasmid-based phylogeny recapitulated that of the main chromosome, indicating limited plasmid horizontal transfer between or within these species. Comparisons of gene content revealed a closed pXO1 and pXO2 pangenome; e.g., plasmids encode <8 unique genes, on average, and a single large fragment deletion of pXO1 in one B.anthracis strain (2000031682) was detected. Collectively, our results provide a more complete view of the genomic diversity of B.anthracis plasmids, their copy number variation, and the virulence potential of other Bacillus species carrying pXO1/pXO2-like plasmids. IMPORTANCE Bacillus anthracis microorganisms are of historical and epidemiological importance and are among the most homogenous bacterial groups known, even though the B.anthracis genome is rich in mobile elements. Mobile elements can trigger the diversification of lineages; therefore, characterizing the extent of genomic variation in a large collection of strains is critical for a complete understanding of the diversity and evolution of the species. Here, we sequenced a large collection of B.anthracis strains (>400) that were recovered from human, animal, and environmental sources around the world. Our results confirmed the remarkable stability of gene content and synteny of the anthrax plasmids and revealed no signal of plasmid exchange between B.anthracis and pathogenic B.cereus isolates but rather predominantly vertical descent. These findings advance our understanding of the biology and pathogenomic evolution of B.anthracis and its plasmids.

Phylogenetic relationship analyses of complicated class Spirotrichea based on transcriptomes from three diverse microbial eukaryotes: Uroleptopsis citrina, Euplotes vannus and Protocruzia tuzeti

Ciliates are one of the eukaryotic unicellular organisms which are thought to be the oldest life forms, and widely geographically distributed. For a variety of reasons, some groups of ciliates have attracted more attention than others, such as the class Spirotrichea and related species with its complicated evolutionary relationships. In this study, we obtained the transcriptome data of three typical ciliates, Uroleptopsis citrina, Euplotes vannus, Protocruzia tuzeti using high throughput sequencing. The genetic relationships were revealed by phylogenomic analysis of 109 genes comprising of 34,882 amino acid residues, and analyses based on SSU rDNA of 55 species, as well as the comparison of gene content among spirotricheans and related species. Our phylogenomic analyses show the Spirotrichea is monophyletic when Protocruzia is excluded, in which four subclasses: Oligotrichia, Choreotrichia, Hypotrichia and Euplotia also formed momophyletic groups respectively. The Hypotrichia was placed as a sister branch to the assemblage, in which two oligotrichs clustered with two choreotrichs. In addition to this, the Protocruziidia was placed in an independent lineage status out of the Spirotrichea. Together with its high binding-related gene content compared to other species and the significant variation in morphological characters, these findings support the removal of Protocruzia from the class Spirotrichea.

Mixta gen. nov., a new genus in the Erwiniaceae.

The Erwiniaceae contain many species of agricultural and clinical importance. Although relationships among most of the genera in this family are relatively well resolved, the phylogenetic placement of several taxa remains ambiguous. In this study, we aimed to address these uncertainties by using a combination of phylogenetic and genomic approaches. Our multilocus sequence analysis and genome-based maximum-likelihood phylogenies revealed that the arsenate-reducing strain IMH and plant-associated strain ATCC 700886, both previously presumptively identified as members of Pantoea, represent novel species of Erwinia. Our data also showed that the taxonomy of Erwinia teleogrylli requires revision as it is clearly excluded from Erwinia and the other genera of the family. Most strikingly, however, five species of Pantoea formed a distinct clade within the Erwiniaceae, where it had a sister group relationship with the Pantoea + Tatumella clade. By making use of gene content comparisons, this new clade is further predicted to encode a range of characters that it shares with or distinguishes it from related genera. We thus propose recognition of this clade as a distinct genus and suggest the name Mixta in reference to the diverse habitats from which its species were obtained, including plants, humans and food products. Accordingly, a description for Mixta gen. nov. is provided to accommodate the four species Mixta calida comb. nov., M. gaviniae comb. nov., M. intestinalis comb. nov. and M. theicola comb. nov., with M. calida as the type species for the genus.

Plastid genome structure and phylogenomics of Nymphaeales: conserved gene order and new insights into relationships

The plastid genomes of early-diverging angiosperms were among the first land plant plastomes investigated. Despite their importance to understanding angiosperm evolution, no investigation has so far compared gene content or gene synteny of these plastid genomes with a focus on the Nymphaeales. Here, we report an evaluation and comparison of gene content, gene synteny and inverted repeat length for a set of 15 plastid genomes of early-diverging angiosperms. Seven plastid genomes of the Nymphaeales were newly sequenced for this investigation. We compare gene order and inverted repeat (IR) length across all genomes, review the gene annotations of previously published genomes, generate a multi-gene alignment of 77 plastid-encoded genes and reconstruct the phylogenetic relationships of the taxa under study. Our results show that gene content and synteny are highly conserved across early-diverging angiosperms: All species analyzed display complete gene synteny when accounting for expansions and contractions of the IRs. This conservation was initially obscured by ambiguous and potentially incorrect gene annotations in previously published genomes. We also report the presence of intact open reading frames across all taxa analyzed. The multi-gene phylogeny displays maximum support for the families Cabombaceae and Hydatellaceae, but no support for a clade of all Nymphaeaceae. It further indicates that the genus Victoria is embedded within Nymphaea. Plastid genomes of Trithuria were found to deviate by numerous substitutions and length changes in the IRs. Phylogenetic analyses further indicate that a previously published plastome named Nymphaea mexicana falls into a clade of N. odorata and should be re-evaluated.

Recombination produces coherent bacterial species clusters in both core and accessory genomes.

Background:Population samples show bacterial genomes can be divided into a core of ubiquitous genes and accessory genes that are present in a fraction of isolates. The ecological significance of this variation in gene content remains unclear. However, microbiologists agree that a bacterial species should be ‘genomically coherent’, even though there is no consensus on how this should be determined.Results:We use a parsimonious model combining diversification in both the core and accessory genome, including mutation, homologous recombination (HR) and horizontal gene transfer (HGT) introducing new loci, to produce a population of interacting clusters of strains with varying genome content. New loci introduced by HGT may then be transferred on by HR. The model fits well to a systematic population sample of 616 pneumococcal genomes, capturing the major features of the population structure with parameter values that agree well with empirical estimates.Conclusions:The model does not include explicit selection on individual genes, suggesting that crude comparisons of gene content may be a poor predictor of ecological function. We identify a clearly divergent subpopulation of pneumococci that are inconsistent with the model and may be considered genomically incoherent with the rest of the population. These strains have a distinct disease tropism and may be rationally defined as a separate species. We also find deviations from the model that may be explained by recent population bottlenecks or spatial structure.

Comparative genomic analyses reveal a lack of a substantial signature of host adaptation inRhodococcus equi(‘Prescottella equi’)

Rhodococcus equi ('Prescottella equi') is a pathogenic actinomycete primarily infecting horses but has emerged as an opportunistic human pathogen. We have sequenced the genome of the type strain of this species, R. equi strain C7(T) , and compared the genome with that of another foal isolate 103S and of a human isolate ATCC 33707. The R. equi strains are closely related to each other and yet distantly related to other rhodococci and Nocardia brasiliensis. The comparison of gene contents among R. equi strains revealed minor differences that could be associated with host adaptation from foals to humans, including the presence of a paa operon in the human isolate, which is potentially involved in pathogenesis.

Sequence Similarity of Clostridium difficile Strains by Analysis of Conserved Genes and Genome Content Is Reflected by Their Ribotype Affiliation

PCR-ribotyping is a broadly used method for the classification of isolates of Clostridium difficile, an emerging intestinal pathogen, causing infections with increased disease severity and incidence in several European and North American countries. We have now carried out clustering analysis with selected genes of numerous C. difficile strains as well as gene content comparisons of their genomes in order to broaden our view of the relatedness of strains assigned to different ribotypes. We analyzed the genomic content of 48 C. difficile strains representing 21 different ribotypes. The calculation of distance matrix-based dendrograms using the neighbor joining method for 14 conserved genes (standard phylogenetic marker genes) from the genomes of the C. difficile strains demonstrated that the genes from strains with the same ribotype generally clustered together. Further, certain ribotypes always clustered together and formed ribotype groups, i.e. ribotypes 078, 033 and 126, as well as ribotypes 002 and 017, indicating their relatedness. Comparisons of the gene contents of the genomes of ribotypes that clustered according to the conserved gene analysis revealed that the number of common genes of the ribotypes belonging to each of these three ribotype groups were very similar for the 078/033/126 group (at most 69 specific genes between the different strains with the same ribotype) but less similar for the 002/017 group (86 genes difference). It appears that the ribotype is indicative not only of a specific pattern of the amplified 16S–23S rRNA intergenic spacer but also reflects specific differences in the nucleotide sequences of the conserved genes studied here. It can be anticipated that the sequence deviations of more genes of C. difficile strains are correlated with their PCR-ribotype. In conclusion, the results of this study corroborate and extend the concept of clonal C. difficile lineages, which correlate with ribotypes affiliation.

New Insights into Dissemination and Variation of the Health Care-Associated Pathogen Acinetobacter baumannii from Genomic Analysis

ABSTRACTAcinetobacter baumannii is a globally important nosocomial pathogen characterized by an increasing incidence of multidrug resistance. Routes of dissemination and gene flow among health care facilities are poorly resolved and are important for understanding the epidemiology of A. baumannii, minimizing disease transmission, and improving patient outcomes. We used whole-genome sequencing to assess diversity and genome dynamics in 49 isolates from one United States hospital system during one year from 2007 to 2008. Core single-nucleotide-variant-based phylogenetic analysis revealed multiple founder strains and multiple independent strains recovered from the same patient yet was insufficient to fully resolve strain relationships, where gene content and insertion sequence patterns added additional discriminatory power. Gene content comparisons illustrated extensive and redundant antibiotic resistance gene carriage and direct evidence of gene transfer, recombination, gene loss, and mutation. Evidence of barriers to gene flow among hospital components was not found, suggesting complex mixing of strains and a large reservoir of A. baumannii strains capable of colonizing patients.

Tracing Patterns of Chloroplast Evolution in Euglenoids: Contributions from Colacium vesiculosum and Strombomonas acuminata (Euglenophyta)

The chloroplast genomes of two photosynthetic euglenoids, Colacium vesiculosum Ehrenberg (128,889 bp), and Strombomonas acuminata (Schmarda) Deflandre (144,167 bp) have been sequenced. These chloroplast genomes in combination with those of Euglena gracilis, Eutreptia viridis, and Eutreptiella gymnastica provide a snapshot of euglenoid chloroplast evolution allowing comparisons of gene content, arrangement, and expansion. The gene content of the five chloroplast genomes is very similar varying only in the presence or absence of, rrn5, roaA, psaI, psaM, rpoA, and two tRNAs. Large gene rearrangements have occurred within the C. vesiculosum and S. acuminata chloroplast genomes. Most of these rearrangements represent repositioning of entire operons rather than single genes. When compared with previously sequenced genomes, C. vesiculosum and S. acuminata chloroplast genomes more closely resemble the E. gracilis chloroplast genome in size of the genome, number of introns, and gene order than they do those of the Eutreptiales. Overall, the chloroplast genomes of these five species show an evolutionary trend toward increased intron number, a decrease in gene density, and substantial rearrangement of gene clusters.

Comparative genome analysis of Spiroplasma melliferumIPMB4A, a honeybee-associated bacterium

BackgroundThe genus Spiroplasma contains a group of helical, motile, and wall-less bacteria in the class Mollicutes. Similar to other members of this class, such as the animal-pathogenic Mycoplasma and the plant-pathogenic ‘Candidatus Phytoplasma’, all characterized Spiroplasma species were found to be associated with eukaryotic hosts. While most of the Spiroplasma species appeared to be harmless commensals of insects, a small number of species have evolved pathogenicity toward various arthropods and plants. In this study, we isolated a novel strain of honeybee-associated S. melliferum and investigated its genetic composition and evolutionary history by whole-genome shotgun sequencing and comparative analysis with other Mollicutes genomes.ResultsThe whole-genome shotgun sequencing of S. melliferum IPMB4A produced a draft assembly that was ~1.1 Mb in size and covered ~80% of the chromosome. Similar to other Spiroplasma genomes that have been studied to date, we found that this genome contains abundant repetitive sequences that originated from plectrovirus insertions. These phage fragments represented a major obstacle in obtaining a complete genome sequence of Spiroplasma with the current sequencing technology. Comparative analysis of S. melliferum IPMB4A with other Spiroplasma genomes revealed that these phages may have facilitated extensive genome rearrangements in these bacteria and contributed to horizontal gene transfers that led to species-specific adaptation to different eukaryotic hosts. In addition, comparison of gene content with other Mollicutes suggested that the common ancestor of the SEM (Spiroplasma, Entomoplasma, and Mycoplasma) clade may have had a relatively large genome and flexible metabolic capacity; the extremely reduced genomes of present day Mycoplasma and ‘Candidatus Phytoplasma’ species are likely to be the result of independent gene losses in these lineages.ConclusionsThe findings in this study highlighted the significance of phage insertions and horizontal gene transfer in the evolution of bacterial genomes and acquisition of pathogenicity. Furthermore, the inclusion of Spiroplasma in comparative analysis has improved our understanding of genome evolution in Mollicutes. Future improvements in the taxon sampling of available genome sequences in this group are required to provide further insights into the evolution of these important pathogens of humans, animals, and plants.