Phylogenomics of the Reproductive Parasite Wolbachia pipientis wMel: A Streamlined Genome Overrun by Mobile Genetic Elements

The complete sequence of the 1,267,782 bp genome of Wolbachia pipientis wMel, an obligate intracellular bacteria of Drosophila melanogaster, has been determined. Wolbachia, which are found in a variety of invertebrate species, are of great interest due to their diverse interactions with different hosts, which range from many forms of reproductive parasitism to mutualistic symbioses. Analysis of the wMel genome, in particular phylogenomic comparisons with other intracellular bacteria, has revealed many insights into the biology and evolution of wMel and Wolbachia in general. For example, the wMel genome is unique among sequenced obligate intracellular species in both being highly streamlined and containing very high levels of repetitive DNA and mobile DNA elements. This observation, coupled with multiple evolutionary reconstructions, suggests that natural selection is somewhat inefficient in wMel, most likely owing to the occurrence of repeated population bottlenecks. Genome analysis predicts many metabolic differences with the closely related Rickettsia species, including the presence of intact glycolysis and purine synthesis, which may compensate for an inability to obtain ATP directly from its host, as Rickettsia can. Other discoveries include the apparent inability of wMel to synthesize lipopolysaccharide and the presence of the most genes encoding proteins with ankyrin repeat domains of any prokaryotic genome yet sequenced. Despite the ability of wMel to infect the germline of its host, we find no evidence for either recent lateral gene transfer between wMel and D. melanogaster or older transfers between Wolbachia and any host. Evolutionary analysis further supports the hypothesis that mitochondria share a common ancestor with the α-Proteobacteria, but shows little support for the grouping of mitochondria with species in the order Rickettsiales. With the availability of the complete genomes of both species and excellent genetic tools for the host, the wMel–D. melanogaster symbiosis is now an ideal system for studying the biology and evolution of Wolbachia infections

Genome Stability of Lyme Disease Spirochetes: Comparative Genomics of Borrelia burgdorferi Plasmids

Lyme disease is the most common tick-borne human illness in North America. In order to understand the molecular pathogenesis, natural diversity, population structure and epizootic spread of the North American Lyme agent, Borrelia burgdorferi sensu stricto, a much better understanding of the natural diversity of its genome will be required. Towards this end we present a comparative analysis of the nucleotide sequences of the numerous plasmids of B. burgdorferi isolates B31, N40, JD1 and 297. These strains were chosen because they include the three most commonly studied laboratory strains, and because they represent different major genetic lineages and so are informative regarding the genetic diversity and evolution of this organism. A unique feature of Borrelia genomes is that they carry a large number of linear and circular plasmids, and this work shows that strains N40, JD1, 297 and B31 carry related but non-identical sets of 16, 20, 19 and 21 plasmids, respectively, that comprise 33–40% of their genomes. We deduce that there are at least 28 plasmid compatibility types among the four strains. The B. burgdorferi ∼900 Kbp linear chromosomes are evolutionarily exceptionally stable, except for a short ≤20 Kbp plasmid-like section at the right end. A few of the plasmids, including the linear lp54 and circular cp26, are also very stable. We show here that the other plasmids, especially the linear ones, are considerably more variable. Nearly all of the linear plasmids have undergone one or more substantial inter-plasmid rearrangements since their last common ancestor. In spite of these rearrangements and differences in plasmid contents, the overall gene complement of the different isolates has remained relatively constant

A behavioral science perspective in the comparative approach to the delivery of health care

This paper, written from a national point of view (that of the United States) has international applicability. It focuses upon problems in the delivery of health care. By suggesting a behavioral science approach to such matters, it offers a better means of raising health levels than other discipline-bound efforts to date. The paper is divided into six parts. Part one addresses itself to the importance of a behavioral science perspective by critiquing several key references which bear directly on the health services system. Part two guides the reader to the available anthropological and sociological literature on health behavior. It comments on the inadequacy of each. Part three provides a description of the comparative approach to health behavior and suggests the extent to which methodological refinements have been made in recent years. Part four discusses the application of the comparative approach to the delivery of health care issue. Part five stresses the magnitude of the need for a behavioral science perspective requiring simultaneous attention to multiple disciplinary dimensions. Part six refers to the behavioral science perspective in specific program settings in the United States, suggesting that this approach will assume an indispensable role in the national effort of evaluation of the health care system. In conclusion, the point is made that a behavioral science perspective as applied to health evaluation adds the important dimension of viewing the medical care crisis as more than a question of availability and efficiency. It is more than the rendering of services in a medical context … the common spirit of the behavioral perspective is to protect the differing value profiles of all participants in the caring process and hence to demonstrate that it is the caring, in a human context, that is the central issue

The complete genome sequence of the gastric pathogen Helicobacter pylori

Helicobacter pylori, strain 26695, has circular genome of 1,667,867 base pairs and 1,590 predicted coding sequences. Sequence analysis indicates that H. pylori has well-developed systems for motility, for scavenging iron, and for DNA restriction and modification. Many putative adhesins, lipoproteins and other outer membrane proteins were identified, underscoring the potential complexity of host-pathogen interaction. Based on the large number of sequence-related genes encoding outer membrane proteins and the presence of homopolymeric tracts and dinucleotide repeats in coding sequences, H. pylori, like several other mucosal pathogens, probably uses recombination and slipped-strand mispairing within repeats as mechanisms for antigenio variation and adaptive evolution. Consistent with its restricted niche, H. pylori has a few regulatory networks, and a limited metabolic repertoire and biosynthetic capacity. Its survival in acid conditions depends, in part, on its ability to establish a positive inside-membrane potential in low pH

Length variation of <i>B. burgdorferi</i> chromosomes.

<p>The relationships among the right end, plasmid-like, chromosomal extensions relative to known plasmids are indicated by gray shading; plasmid sizes are not drawn exactly to scale. There is a 1053 bp deletion and a 17 bp insertion in the 297 lp28-1 plasmid relative to the B31 extension. It is assumed that the 297 chromosome is essentially identical to that strain Sh-2-82 (see text and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033280#pone.0033280-Huang1" target="_blank">[51]</a>).</p

Organizational and open reading frame relationships among four lp38 plasmids.

<p>Maps of the four lp38s are labeled as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033280#pone-0033280-g008" target="_blank">Figure 8</a>. Yellow shading between maps marks regions of high nucleotide sequence similarity (percent identity values in black text). The pink horizontal bar indicates the region of 63 bp repeats in JD1 lp38; and blue arrows represent predicted transporter genes.</p

<i>B. burgdorferi</i> plasmids present in four isolates.

a<p>Plasmids known to be in some cultures of the indicated strain, but which were not present in the sequenced culture. Their sequences remain undetermined.</p>b<p>Structural differences from otherwise organizationally similar plasmids are indicated as follows: trunc, truncated compared to other homologous plasmids; int, B31 cp32-10 is integrated into plasmid lp56; fused, JD1 cp32-1 and cp32-5 are fused into one large circular “cp32-1+5” plasmid.</p>c<p>In some B31 cultures the plasmid cp32-7 is replaced by cp32-2 <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033280#pone.0033280-Casjens2" target="_blank">[12]</a>. These two plasmids have the same apparent compatibility and appear to be prophage DNAs. Since it seems unlikely that they can exist in the same cell, and they are expected to be able to move between strains, one of them may have been inadvertently introduced in the laboratory. We use cp32-7 for this compatibility type since it is the one that is present in the completely sequenced B31 genome.</p