Amazonian deforestation and soil biodiversity.

Clearance and perturbation of Amazonian forests are one of the greatest threats to tropical biodiversity conservation of our times. A better understanding of how soil communities respond to Amazonian deforestation is crucially needed to inform policy interventions that effectively protect biodiversity and the essential ecosystem services it provides. We assessed the impact of deforestation and ecosystem conversion to arable land on Amazonian soil biodiversity through a meta-analysis. We analyzed 274 pairwise comparisons of soil biodiversity in Amazonian primary forests and sites under different stages of deforestation and land-use conversion: disturbed (wildfire and selective logging) and slash-and-burnt forests, pastures, and cropping systems. Overall, 60% and 51% of responses of soil macrofauna and microbial community attributes (i.e., abundance, biomass, richness, and diversity indexes) to deforestation were negative, respectively. We found few studies on mesofauna (e.g., microarthropods) and microfauna (e.g., protozoa and nematodes), so those groups could not be analyzed. Macrofauna abundance and biomass were more vulnerable to the displacement of forests by pastures than by agricultural fields, whereas microbes showed the opposite pattern. Effects of Amazonian deforestation on macrofauna were more detrimental at sites with mean annual precipitation >1900 mm, and higher losses of microbes occurred in highly acidic soils (pH < 4.5). Limited geographic coverage, omission of meso- and microfauna, and low taxonomic resolution were main factors impairing generalizations from the data set. Few studies assessed the impacts of within-forest disturbance (wildfires and selective logging) on soil species in Amazonia, where logging operations rapidly expand across public lands and more frequent severe dry seasons are increasing the prevalence of wildfires.

Deforestación en el Amazonas y Biodiversidad del Suelo Resumen Actualmente, el despeje y la perturbación de los bosques del Amazonas son las principales amenazas para la conservación de la biodiversidad tropical. Se requiere urgentemente de un mejor entendimiento sobre cómo las comunidades del suelo responden a la deforestación amazónica para informar a las intervenciones políticas que protegen efectivamente a la biodiversidad y a los servicios ambientales esenciales que proporciona. Evaluamos el impacto de la deforestación y la conversión del ecosistema a suelo arable sobre la biodiversidad del suelo amazónico por medio de un meta-análisis. Analizamos 274 comparaciones por pares de la biodiversidad del suelo amazónico en bosques primarios y sitios bajo diferentes etapas de deforestación y conversión de uso de suelo: bosques perturbados (incendios forestales y tala selectiva) y de corte-y-quema, pasturas, y sistemas agrícolas. En general, el 60% y el 51% de las respuestas de los atributos (es decir, abundancia, biomasa, riqueza, e índices de biodiversidad) de la macrofauna del suelo y de las comunidades microbianas ante la deforestación fueron negativas, respectivamente. Encontramos pocos estudios sobre la mesofauna (p. ej.: microartrópodos) y la microfauna (p. ej.: protozoarios y nematodos), así que estos grupos no pudieron ser analizados. La abundancia de la macrofauna y la biomasa fueron más vulnerables al desplazamiento de bosques por las pasturas que por los campos agrícolas, mientras que los microbios mostraron el patrón opuesto. Los efectos de la deforestación amazónica sobre la macrofauna fueron más dañinos en sitios con una precipitación anual media mayor a los 1,900 mm, y ocurrieron pérdidas más elevadas de microbios en suelos con una acidez alta (pH < 4.5). La cobertura geográfica limitada, la omisión de la mesofauna y la microfauna, y la baja resolución taxonómica fueron los factores principales que obstaculizaron las generalizaciones del conjunto de datos. Pocos estudios evaluaron los impactos de las perturbaciones internas del bosque (incendios forestales y tala selectiva) sobre las especies del suelo amazónico, a la vez que las operaciones de tala se expanden rápidamente en los terrenos públicos y la ocurrencia con mayor frecuencia de temporadas con sequía grave aumentan la prevalencia de los incendios forestales.

Curation, integration and visualization of bacterial virulence factors in PATRIC.

MOTIVATION: We've developed a highly curated bacterial virulence factor (VF) library in PATRIC (Pathosystems Resource Integration Center, www.patricbrc.org) to support infectious disease research. Although several VF databases are available, there is still a need to incorporate new knowledge found in published experimental evidence and integrate these data with other information known for these specific VF genes, including genomic and other omics data. This integration supports the identification of VFs, comparative studies and hypothesis generation, which facilitates the understanding of virulence and pathogenicity. RESULTS: We have manually curated VFs from six prioritized NIAID (National Institute of Allergy and Infectious Diseases) category A-C bacterial pathogen genera, Mycobacterium, Salmonella, Escherichia, Shigella, Listeria and Bartonella, using published literature. This curated information on virulence has been integrated with data from genomic functional annotations, trancriptomic experiments, protein-protein interactions and disease information already present in PATRIC. Such integration gives researchers access to a broad array of information about these individual genes, and also to a suite of tools to perform comparative genomic and transcriptomics analysis that are available at PATRIC. AVAILABILITY AND IMPLEMENTATION: All tools and data are freely available at PATRIC (http://patricbrc.org). SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

PATRIC, the bacterial bioinformatics database and analysis resource.

The Pathosystems Resource Integration Center (PATRIC) is the all-bacterial Bioinformatics Resource Center (BRC) (http://www.patricbrc.org). A joint effort by two of the original National Institute of Allergy and Infectious Diseases-funded BRCs, PATRIC provides researchers with an online resource that stores and integrates a variety of data types [e.g. genomics, transcriptomics, protein-protein interactions (PPIs), three-dimensional protein structures and sequence typing data] and associated metadata. Datatypes are summarized for individual genomes and across taxonomic levels. All genomes in PATRIC, currently more than 10,000, are consistently annotated using RAST, the Rapid Annotations using Subsystems Technology. Summaries of different data types are also provided for individual genes, where comparisons of different annotations are available, and also include available transcriptomic data. PATRIC provides a variety of ways for researchers to find data of interest and a private workspace where they can store both genomic and gene associations, and their own private data. Both private and public data can be analyzed together using a suite of tools to perform comparative genomic or transcriptomic analysis. PATRIC also includes integrated information related to disease and PPIs. All the data and integrated analysis and visualization tools are freely available. This manuscript describes updates to the PATRIC since its initial report in the 2007 NAR Database Issue.

The condition-dependent transcriptional landscape of Burkholderia pseudomallei.

Burkholderia pseudomallei (Bp), the causative agent of the often-deadly infectious disease melioidosis, contains one of the largest prokaryotic genomes sequenced to date, at 7.2 Mb with two large circular chromosomes (1 and 2). To comprehensively delineate the Bp transcriptome, we integrated whole-genome tiling array expression data of Bp exposed to >80 diverse physical, chemical, and biological conditions. Our results provide direct experimental support for the strand-specific expression of 5,467 Sanger protein-coding genes, 1,041 operons, and 766 non-coding RNAs. A large proportion of these transcripts displayed condition-dependent expression, consistent with them playing functional roles. The two Bp chromosomes exhibited dramatically different transcriptional landscapes--Chr 1 genes were highly and constitutively expressed, while Chr 2 genes exhibited mosaic expression where distinct subsets were expressed in a strongly condition-dependent manner. We identified dozens of cis-regulatory motifs associated with specific condition-dependent expression programs, and used the condition compendium to elucidate key biological processes associated with two complex pathogen phenotypes--quorum sensing and in vivo infection. Our results demonstrate the utility of a Bp condition-compendium as a community resource for biological discovery. Moreover, the observation that significant portions of the Bp virulence machinery can be activated by specific in vitro cues provides insights into Bp's capacity as an "accidental pathogen", where genetic pathways used by the bacterium to survive in environmental niches may have also facilitated its ability to colonize human hosts.

Comparative phylogenomics and evolution of the Brucellae reveal a path to virulence.

Brucella species include important zoonotic pathogens that have a substantial impact on both agriculture and human health throughout the world. Brucellae are thought of as "stealth pathogens" that escape recognition by the host innate immune response, modulate the acquired immune response, and evade intracellular destruction. We analyzed the genome sequences of members of the family Brucellaceae to assess its evolutionary history from likely free-living soil-based progenitors into highly successful intracellular pathogens. Phylogenetic analysis split the genus into two groups: recently identified and early-dividing "atypical" strains and a highly conserved "classical" core clade containing the major pathogenic species. Lateral gene transfer events brought unique genomic regions into Brucella that differentiated them from Ochrobactrum and allowed the stepwise acquisition of virulence factors that include a type IV secretion system, a perosamine-based O antigen, and systems for sequestering metal ions that are absent in progenitors. Subsequent radiation within the core Brucella resulted in lineages that appear to have evolved within their preferred mammalian hosts, restricting their virulence to become stealth pathogens capable of causing long-term chronic infections.

A Rickettsia genome overrun by mobile genetic elements provides insight into the acquisition of genes characteristic of an obligate intracellular lifestyle.

We present the draft genome for the Rickettsia endosymbiont of Ixodes scapularis (REIS), a symbiont of the deer tick vector of Lyme disease in North America. Among Rickettsia species (Alphaproteobacteria: Rickettsiales), REIS has the largest genome sequenced to date (>2 Mb) and contains 2,309 genes across the chromosome and four plasmids (pREIS1 to pREIS4). The most remarkable finding within the REIS genome is the extraordinary proliferation of mobile genetic elements (MGEs), which contributes to a limited synteny with other Rickettsia genomes. In particular, an integrative conjugative element named RAGE (for Rickettsiales amplified genetic element), previously identified in scrub typhus rickettsiae (Orientia tsutsugamushi) genomes, is present on both the REIS chromosome and plasmids. Unlike the pseudogene-laden RAGEs of O. tsutsugamushi, REIS encodes nine conserved RAGEs that include F-like type IV secretion systems similar to that of the tra genes encoded in the Rickettsia bellii and R. massiliae genomes. An unparalleled abundance of encoded transposases (>650) relative to genome size, together with the RAGEs and other MGEs, comprise ~35% of the total genome, making REIS one of the most plastic and repetitive bacterial genomes sequenced to date. We present evidence that conserved rickettsial genes associated with an intracellular lifestyle were acquired via MGEs, especially the RAGE, through a continuum of genomic invasions. Robust phylogeny estimation suggests REIS is ancestral to the virulent spotted fever group of rickettsiae. As REIS is not known to invade vertebrate cells and has no known pathogenic effects on I. scapularis, its genome sequence provides insight on the origin of mechanisms of rickettsial pathogenicity.

Abscisic acid regulates inflammation via ligand-binding domain-independent activation of peroxisome proliferator-activated receptor gamma.

Abscisic acid (ABA) has shown efficacy in the treatment of diabetes and inflammation; however, its molecular targets and the mechanisms of action underlying its immunomodulatory effects remain unclear. This study investigates the role of peroxisome proliferator-activated receptor γ (PPAR γ) and lanthionine synthetase C-like 2 (LANCL2) as molecular targets for ABA. We demonstrate that ABA increases PPAR γ reporter activity in RAW 264.7 macrophages and increases ppar γ expression in vivo, although it does not bind to the ligand-binding domain of PPAR γ. LANCL2 knockdown studies provide evidence that ABA-mediated activation of macrophage PPAR γ is dependent on lancl2 expression. Consistent with the association of LANCL2 with G proteins, we provide evidence that ABA increases cAMP accumulation in immune cells. ABA suppresses LPS-induced prostaglandin E(2) and MCP-1 production via a PPAR γ-dependent mechanism possibly involving activation of PPAR γ and suppression of NF-κB and nuclear factor of activated T cells. LPS challenge studies in PPAR γ-expressing and immune cell-specific PPAR γ null mice demonstrate that ABA down-regulates toll-like receptor 4 expression in macrophages and T cells in vivo through a PPAR γ-dependent mechanism. Global transcriptomic profiling and confirmatory quantitative RT-PCR suggest novel candidate targets and demonstrate that ABA treatment mitigates the effect of LPS on the expression of genes involved in inflammation, metabolism, and cell signaling, in part, through PPAR γ. In conclusion, ABA decreases LPS-mediated inflammation and regulates innate immune responses through a bifurcating pathway involving LANCL2 and an alternative, ligand-binding domain-independent mechanism of PPAR γ activation.

Integration and visualization of host-pathogen data related to infectious diseases.

MOTIVATION: Infectious disease research is generating an increasing amount of disparate data on pathogenic systems. There is a growing need for resources that effectively integrate, analyze, deliver and visualize these data, both to improve our understanding of infectious diseases and to facilitate the development of strategies for disease control and prevention. RESULTS: We have developed Disease View, an online host-pathogen resource that enables infectious disease-centric access, analysis and visualization of host-pathogen interactions. In this resource, we associate infectious diseases with corresponding pathogens, provide information on pathogens, pathogen virulence genes and the genetic and chemical evidences for the human genes that are associated with the diseases. We also deliver the relationships between pathogens, genes and diseases in an interactive graph and provide the geolocation reports of associated diseases around the globe in real time. Unlike many other resources, we have applied an iterative, user-centered design process to the entire resource development, including data acquisition, analysis and visualization. AVAILABILITY AND IMPLEMENTATION: Freely available at http://www.patricbrc.org; all major web browsers supported. CONTACT: cmao@vbi.vt.edu SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

PATRIC: the comprehensive bacterial bioinformatics resource with a focus on human pathogenic species.

Funded by the National Institute of Allergy and Infectious Diseases, the Pathosystems Resource Integration Center (PATRIC) is a genomics-centric relational database and bioinformatics resource designed to assist scientists in infectious-disease research. Specifically, PATRIC provides scientists with (i) a comprehensive bacterial genomics database, (ii) a plethora of associated data relevant to genomic analysis, and (iii) an extensive suite of computational tools and platforms for bioinformatics analysis. While the primary aim of PATRIC is to advance the knowledge underlying the biology of human pathogens, all publicly available genome-scale data for bacteria are compiled and continually updated, thereby enabling comparative analyses to reveal the basis for differences between infectious free-living and commensal species. Herein we summarize the major features available at PATRIC, dividing the resources into two major categories: (i) organisms, genomes, and comparative genomics and (ii) recurrent integration of community-derived associated data. Additionally, we present two experimental designs typical of bacterial genomics research and report on the execution of both projects using only PATRIC data and tools. These applications encompass a broad range of the data and analysis tools available, illustrating practical uses of PATRIC for the biologist. Finally, a summary of PATRIC's outreach activities, collaborative endeavors, and future research directions is provided.

PIG--the pathogen interaction gateway.

Protein-protein interactions (PPIs) play a vital role in initiating infection in a number of pathogens. Identifying which interactions allow a pathogen to infect its host can help us to understand methods of pathogenesis and provide potential targets for therapeutics. Public resources for studying host-pathogen systems, in particular PPIs, are scarce. To facilitate the study of host-pathogen PPIs, we have collected and integrated host-pathogen PPI (HP-PPI) data from a number of public resources to create the Pathogen Interaction Gateway (PIG). PIG provides a text based search and a BLAST interface for searching the HP-PPI data. Each entry in PIG includes information such as the functional annotations and the domains present in the interacting proteins. PIG provides links to external databases to allow for easy navigation among the various websites. Additionally, PIG includes a tool for visualizing a single HP-PPI network or two HP-PPI networks. PIG can be accessed at http://pig.vbi.vt.edu.

Phylogeny of gammaproteobacteria.

The phylogeny of the large bacterial class Gammaproteobacteria has been difficult to resolve. Here we apply a telescoping multiprotein approach to the problem for 104 diverse gammaproteobacterial genomes, based on a set of 356 protein families for the whole class and even larger sets for each of four cohesive subregions of the tree. Although the deepest divergences were resistant to full resolution, some surprising patterns were strongly supported. A representative of the Acidithiobacillales routinely appeared among the outgroup members, suggesting that in conflict with rRNA-based phylogenies this order does not belong to Gammaproteobacteria; instead, it (and, independently, "Mariprofundus") diverged after the establishment of the Alphaproteobacteria yet before the betaproteobacteria/gammaproteobacteria split. None of the orders Alteromonadales, Pseudomonadales, or Oceanospirillales were monophyletic; we obtained strong support for clades that contain some but exclude other members of all three orders. Extreme amino acid bias in the highly A+T-rich genome of Candidatus Carsonella prevented its reliable placement within Gammaproteobacteria, and high bias caused artifacts that limited the resolution of the relationships of other insect endosymbionts, which appear to have had multiple origins, although the unbiased genome of the endosymbiont Sodalis acted as an attractor for them. Instability was observed for the root of the Enterobacteriales, with nearly equal subsets of the protein families favoring one or the other of two alternative root positions; the nematode symbiont Photorhabdus was identified as a disruptor whose omission helped stabilize the Enterobacteriales root.

Phylogenomics reveals a diverse Rickettsiales type IV secretion system.

With an obligate intracellular lifestyle, Alphaproteobacteria of the order Rickettsiales have inextricably coevolved with their various eukaryotic hosts, resulting in small, reductive genomes and strict dependency on host resources. Unsurprisingly, large portions of Rickettsiales genomes encode proteins involved in transport and secretion. One particular transporter that has garnered recent attention from researchers is the type IV secretion system (T4SS). Homologous to the well-studied archetypal vir T4SS of Agrobacterium tumefaciens, the Rickettsiales vir homolog (rvh) T4SS is characterized primarily by duplication of several of its genes and scattered genomic distribution of all components in several conserved islets. Phylogeny estimation suggests a single event of ancestral acquirement of the rvh T4SS, likely from a nonalphaproteobacterial origin. Bioinformatics analysis of over 30 Rickettsiales genome sequences illustrates a conserved core rvh scaffold (lacking only a virB5 homolog), with lineage-specific diversification of several components (rvhB1, rvhB2, and rvhB9b), likely a result of modifications to cell envelope structure. This coevolution of the rvh T4SS and cell envelope morphology is probably driven by adaptations to various host cells, identifying the transporter as an important target for vaccine development. Despite the genetic intractability of Rickettsiales, recent advancements have been made in the characterization of several components of the rvh T4SS, as well as its putative regulators and substrates. While current data favor a role in effector translocation, functions in DNA uptake and release and/or conjugation cannot at present be ruled out, especially considering that a mechanism for plasmid transfer in Rickettsia spp. has yet to be proposed.

Sinorhizobium meliloti 1021 loss-of-function deletion mutation in chvI and its phenotypic characteristics.

Bacterial two-component regulatory systems (TCS) are common components of complex regulatory networks and cascades. In Sinorhizobium meliloti, the TCS ExoS/ChvI controls exopolysaccharide succinoglycan production and flagellum biosynthesis. Although this system plays a crucial role in establishing the symbiosis between S. meliloti and its host plant, it is not well characterized. Attempts to generate complete loss-of-function mutations in either exoS or chvI in S. meliloti have been unsuccessful; thus, it was previously suggested that exoS or chvI are essential genes for bacterial cell growth. We constructed a chvI mutant by completely deleting the open reading frame encoding this gene. The mutant strain failed to grow on complex medium, exhibited lower tolerance to acidic condition, produced significantly less poly-3-hydroxybutyrate than the wild type, was hypermotile, and exhibited an altered lipopolysaccharide profile. In addition, this mutant was defective in symbiosis with Medicago truncatula and M. sativa (alfalfa), although it induced root hair deformation as efficiently as the wild type. Together, our results demonstrate that ChvI is intimately involved in regulatory networks involving the cell envelope and metabolism; however, its precise role within the regulatory network remains to be determined.

Transcriptome sequencing and comparative analysis of cucumber flowers with different sex types.

BACKGROUND: Cucumber, Cucumis sativus L., is an economically and nutritionally important crop of the Cucurbitaceae family and has long served as a primary model system for sex determination studies. Recently, the sequencing of its whole genome has been completed. However, transcriptome information of this species is still scarce, with a total of around 8,000 Expressed Sequence Tag (EST) and mRNA sequences currently available in GenBank. In order to gain more insights into molecular mechanisms of plant sex determination and provide the community a functional genomics resource that will facilitate cucurbit research and breeding, we performed transcriptome sequencing of cucumber flower buds of two near-isogenic lines, WI1983G, a gynoecious plant which bears only pistillate flowers, and WI1983H, a hermaphroditic plant which bears only bisexual flowers. RESULT: Using Roche-454 massive parallel pyrosequencing technology, we generated a total of 353,941 high quality EST sequences with an average length of 175bp, among which 188,255 were from gynoecious flowers and 165,686 from hermaphroditic flowers. These EST sequences, together with approximately 5,600 high quality cucumber EST and mRNA sequences available in GenBank, were clustered and assembled into 81,401 unigenes, of which 28,452 were contigs and 52,949 were singletons. The unigenes and ESTs were further mapped to the cucumber genome and more than 500 alternative splicing events were identified in 443 cucumber genes. The unigenes were further functionally annotated by comparing their sequences to different protein and functional domain databases and assigned with Gene Ontology (GO) terms. A biochemical pathway database containing 343 predicted pathways was also created based on the annotations of the unigenes. Digital expression analysis identified approximately 200 differentially expressed genes between flowers of WI1983G and WI1983H and provided novel insights into molecular mechanisms of plant sex determination process. Furthermore, a set of SSR motifs and high confidence SNPs between WI1983G and WI1983H were identified from the ESTs, which provided the material basis for future genetic linkage and QTL analysis. CONCLUSION: A large set of EST sequences were generated from cucumber flower buds of two different sex types. Differentially expressed genes between these two different sex-type flowers, as well as putative SSR and SNP markers, were identified. These EST sequences provide valuable information to further understand molecular mechanisms of plant sex determination process and forms a rich resource for future functional genomics analysis, marker development and cucumber breeding.

The landscape of human proteins interacting with viruses and other pathogens.

Infectious diseases result in millions of deaths each year. Mechanisms of infection have been studied in detail for many pathogens. However, many questions are relatively unexplored. What are the properties of human proteins that interact with pathogens? Do pathogens interact with certain functional classes of human proteins? Which infection mechanisms and pathways are commonly triggered by multiple pathogens? In this paper, to our knowledge, we provide the first study of the landscape of human proteins interacting with pathogens. We integrate human-pathogen protein-protein interactions (PPIs) for 190 pathogen strains from seven public databases. Nearly all of the 10,477 human-pathogen PPIs are for viral systems (98.3%), with the majority belonging to the human-HIV system (77.9%). We find that both viral and bacterial pathogens tend to interact with hubs (proteins with many interacting partners) and bottlenecks (proteins that are central to many paths in the network) in the human PPI network. We construct separate sets of human proteins interacting with bacterial pathogens, viral pathogens, and those interacting with multiple bacteria and with multiple viruses. Gene Ontology functions enriched in these sets reveal a number of processes, such as cell cycle regulation, nuclear transport, and immune response that participate in interactions with different pathogens. Our results provide the first global view of strategies used by pathogens to subvert human cellular processes and infect human cells. Supplementary data accompanying this paper is available at http://staff.vbi.vt.edu/dyermd/publications/dyer2008a.html.

Modulation of hepatic PPAR expression during Ft LVS LPS-induced protection from Francisella tularensis LVS infection.

BACKGROUND: It has been shown previously that administration of Francisella tularensis (Ft) Live Vaccine Strain (LVS) lipopolysaccharide (LPS) protects mice against subsequent challenge with Ft LVS and blunts the pro-inflammatory cytokine response. METHODS: To further investigate the molecular mechanisms that underlie Ft LVS LPS-mediated protection, we profiled global hepatic gene expression following Ft LVS LPS or saline pre-treatment and subsequent Ft LVS challenge using Affymetrix arrays. RESULTS: A large number of genes (> 3,000) were differentially expressed at 48 hours post-infection. The degree of modulation of inflammatory genes by infection was clearly attenuated by pre-treatment with Ft LVS LPS in the surviving mice. However, Ft LVS LPS alone had a subtle effect on the gene expression profile of the uninfected mice. By employing gene set enrichment analysis, we discovered significant up-regulation of the fatty acid metabolism pathway, which is regulated by peroxisome proliferator activated receptors (PPARs). CONCLUSIONS: We hypothesize that the LPS-induced blunting of pro-inflammatory response in mouse is, in part, mediated by PPARs (alpha and gamma).

A typhus group-specific protease defies reductive evolution in rickettsiae.

Phylogenomics reveals extreme gene loss in typhus group (TG) rickettsiae relative to the levels for other rickettsial lineages. We report here a curious protease-encoding gene (ppcE) that is conserved only in TG rickettsiae. As a possible determinant of host pathogenicity, ppcE warrants consideration in the development of therapeutics against epidemic and murine typhus.

Analysis of ten Brucella genomes reveals evidence for horizontal gene transfer despite a preferred intracellular lifestyle.

The facultative intracellular bacterial pathogen Brucella infects a wide range of warm-blooded land and marine vertebrates and causes brucellosis. Currently, there are nine recognized Brucella species based on host preferences and phenotypic differences. The availability of 10 different genomes consisting of two chromosomes and representing six of the species allowed for a detailed comparison among themselves and relatives in the order Rhizobiales. Phylogenomic analysis of ortholog families shows limited divergence but distinct radiations, producing four clades as follows: Brucella abortus-Brucella melitensis, Brucella suis-Brucella canis, Brucella ovis, and Brucella ceti. In addition, Brucella phylogeny does not appear to reflect the phylogeny of Brucella species' preferred hosts. About 4.6% of protein-coding genes seem to be pseudogenes, which is a relatively large fraction. Only B. suis 1330 appears to have an intact beta-ketoadipate pathway, responsible for utilization of plant-derived compounds. In contrast, this pathway in the other species is highly pseudogenized and consistent with the "domino theory" of gene death. There are distinct shared anomalous regions (SARs) found in both chromosomes as the result of horizontal gene transfer unique to Brucella and not shared with its closest relative Ochrobactrum, a soil bacterium, suggesting their acquisition occurred in spite of a predominantly intracellular lifestyle. In particular, SAR 2-5 appears to have been acquired by Brucella after it became intracellular. The SARs contain many genes, including those involved in O-polysaccharide synthesis and type IV secretion, which if mutated or absent significantly affect the ability of Brucella to survive intracellularly in the infected host.

Comparative genomics reveal extensive transposon-mediated genomic plasticity and diversity among potential effector proteins within the genus Coxiella.

Genetically distinct isolates of Coxiella burnetii, the cause of human Q fever, display different phenotypes with respect to in vitro infectivity/cytopathology and pathogenicity for laboratory animals. Moreover, correlations between C. burnetii genomic groups and human disease presentation (acute versus chronic) have been described, suggesting that isolates have distinct virulence characteristics. To provide a more-complete understanding of C. burnetii's genetic diversity, evolution, and pathogenic potential, we deciphered the whole-genome sequences of the K (Q154) and G (Q212) human chronic endocarditis isolates and the naturally attenuated Dugway (5J108-111) rodent isolate. Cross-genome comparisons that included the previously sequenced Nine Mile (NM) reference isolate (RSA493) revealed both novel gene content and disparate collections of pseudogenes that may contribute to isolate virulence and other phenotypes. While C. burnetii genomes are highly syntenous, recombination between abundant insertion sequence (IS) elements has resulted in genome plasticity manifested as chromosomal rearrangement of syntenic blocks and DNA insertions/deletions. The numerous IS elements, genomic rearrangements, and pseudogenes of C. burnetii isolates are consistent with genome structures of other bacterial pathogens that have recently emerged from nonpathogens with expanded niches. The observation that the attenuated Dugway isolate has the largest genome with the fewest pseudogenes and IS elements suggests that this isolate's lineage is at an earlier stage of pathoadaptation than the NM, K, and G lineages.

Variations on the tmRNA gene.

tmRNA employs both tRNA-like and mRNA-like properties as it rescues stalled bacterial ribosomes, while targeting the defective mRNA and incomplete nascent protein for degradation. We describe variation of the tmRNA gene (ssrA) and how it informs tmRNA structure and function. Endosymbiont tmRNAs tend to lose secondary structure and length in the mRNA-like region as nucleotide composition drifts with that of the whole genome. A dramatic gene structure variation is circular permutation, which produces two-piece tmRNAs in three bacterial lineages; new sequences blur these lineages. We present evidence that Sinorhizobium two-piece tmRNA retains the 5'-triphosphate of transcriptional initiation and predict a new structure at the 5' end of cyanobacterial two-piece tmRNA precursor. ssrA is a target for some mobile DNAs and a passenger on others. It has been found interrupted (but not functionally disrupted) by mobile elements such as group I introns, genomic islands and palindromic elements. The alphaproteobacterial permuted genes are significantly less frequently interrupted by genomic islands than are their standard counterparts, yet are a hotspot for insertion or swapping of rickettsial palindromic elements, in contrast to other rickettsial loci that show steady decay of a single ancestral element. Bacteriophages, plasmids and genomic islands can carry tmRNA genes; we describe a native bacterial ssrA disrupted by insertion of a genomic island that carries its own ssrA, a genome encoding both one- and two-piece tmRNA, and a phage encoding a tmRNA variant lacking the mRNA-like function, which may counteract host tmRNA during infection.