Selected examples of phenotypes resulting from natural <i>Wolbachia</i> symbioses.

<p><i>Wolbachia</i> produces a large spectrum of phenotypes in their hosts ranging from parasitic to mutualistic traits existing as either facultative relationships or associations that have evolved to become obligate. Reproductive parasitism by <i>Wolbachia</i> is well recognised. For example, in the ladybird <i>Adalia bipunctata</i>, infection results in death of infected males during development to the benefit of female siblings (male killing) <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003224#pntd.0003224-Hurst1" target="_blank">[72]</a>; in the woodlouse <i>Armadillidium vulgare</i>, infection causes development of infected genetic males into females (feminisation) <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003224#pntd.0003224-Bouchon1" target="_blank">[73]</a>; and in the mosquito <i>Culex pipiens</i>, <i>Wolbachia</i> strain <i>w</i>Pip produces cytoplasmic incompatibility (CI), in which crosses between infected males and uninfected females result in embryonic death. <i>Wolbachia</i> symbioses may also provide benefits to the host, such as increases in fecundity and longevity in <i>Drosophila melanogaster</i><a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003224#pntd.0003224-Fry1" target="_blank">[74]</a>. In some species, mutualistic traits coexist with reproductive phenotypes, such as in <i>Culex pipiens</i>, where the CI-inducing strain <i>w</i>Pip also provides protection from mortality associated with <i>Plasmodium relictum</i><a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003224#pntd.0003224-Zl1" target="_blank">[13]</a>. In some host species, all individuals are infected and this association is often mutualistic, as in the bedbug <i>Cimex lectularius</i> in which <i>Wolbachia</i> supplies essential B vitamins <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003224#pntd.0003224-Hosokawa1" target="_blank">[10]</a>, or in the filarial parasite <i>Onchocerca ochengi</i>, where the presence of the bacteria is associated with the vertebrate host mounting an ineffective immune response <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003224#pntd.0003224-Hansen1" target="_blank">[75]</a>. However, in the parasitic wasp <i>Asobara tabida</i>, strain <i>wAtab3</i> is essential for oogenesis, making the relationship obligatory without any known benefits to the host <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0003224#pntd.0003224-Kremer2" target="_blank">[43]</a>.</p

The proposed haem synthesis pathway in <i>Wolbachia</i>, showing structural intermediates.

<p>Enzymes are represented by red boxes, which contain the protein name in <i>Wolbachia</i> and the abbreviated enzyme name: ALAS, 5-aminolevulinate synthase; ALAD, 5-aminolevulinate dehydratase; PBGB, porphobilinogen deaminase; UROS, uroporphyrinogen III synthase; UROD, uroporphyrinogen III decarboxylase; CPO, coproporphyrinogen III oxidase; PPO, protoporphyrinogen IX oxidase; FC, ferrochelatase. Inhibitors of the pathway are represented by blue boxes, for which abbreviations used are as in the text.</p