By contrast, current knowledge on symbionts of nematodes is still mainly restricted to Wolbachia

and its interaction with filarial worms that lead to increased pathogenicity of the infected nematode. In this review article, we aim to highlight the main characteristics of symbionts in term of their ecology, host cell interactions, parasitism and co-evolution, in order to stimulate future research in a field that remains largely unexplored selleck chemicals despite the availability of modern tools. Endosymbiosis is a symbiosis in which one symbiont dwells within the body of the other. Usually, when talking about endosymbionts, we refer to bacteria or less frequently to fungi living inside the eukaryotic cell or simply inside the body. Interestingly, the endosymbiotic

theory first articulated by the Russian botanist Konstantin Mereschkowski in 1905 (Emelyanov, 2007) describes chloroplasts, mitochondria and other organelles as originating from bacterial endosymbionts. Nearly 90 years ago, Paul Buchner, the father of symbiosis research, documented a remarkable array of both endosymbiotic fungal R428 and bacterial associates of arthropods (Buchner, 1965). More recently, evidence has also emerged that bacterial symbionts are present in a large variety of additional eukaryotes, including nematodes, amoebae and plants (see Table 1 for a summary of selected discoveries illuminating research on symbionts). In the present review, we will focus on bacterial symbionts associated with nematodes, arthropods and free-living amoebae. Nematodes

or ‘roundworms’ form a highly successful and abundant group of organisms found in every ecosystem on Earth. Considering their ubiquity and enormous diversity, it is surprising that only relatively few examples of bacterial endosymbioses have been described in nematodes compared with amoebae and arthropods. Of these few examples, only three have been investigated in sufficient detail to unravel some Cell press of the biological features of the symbiotic relationship. The most extensively studied systems are the closely related Gammaproteobacteria, Photorhabdus and Xenorhabdus, which colonize the guts of Heterorhabditis and Steinemema nematodes, respectively (see Goodrich-Blair & Clarke, 2007; Herbert & Goodrich-Blair, 2007; Clarke, 2008; for in-depth reviews). The bacteria have intricate and distinct roles in the nematode’s life cycle. On entering its insect prey, the infective juvenile stage of the nematode regurgitates its bacteria into the haemolymph, which rapidly grows and kills the insect, releasing nutrients to support the growth and development of the nematode. After the adults reproduce, a process that is dependent upon symbionts, environmental cues stimulate the progeny to enter the infective juvenile stage, which becomes re-colonized with one or two bacteria through maternal inoculation.