Nematode-bacterial associations

The most intimate of the bacterial-nematode associations involves Wolbachia, a genus of rickettsia-like, alpha proteobacteria found in obligate intracellular association with a wide variety of arthropods, and a now well-characterized association with B. malayi and Dirofilaria immitis (Chapter 2). Although not formally identified as Wolbachia, the presence of rickett-sia-like organisms has been observed, principally in the reproductive tracts of Globodera females (Shepherd et al., 1973) and males (Walsh et al., 1983) and in Heterodera larvae (Endo, 1979). 

Nematodes that are possibly bacteriophagous also increase after the treatment (Yamanaka 1995a, 1995c), a possible reflection of increased bacterial numbers. This phenomenon has also been observed in association with decomposing pig carcasses (Carter et al., unpublished). The appearance of the possible nematode parasite Rhopalomyces elegans var. minor (see Section 4.2.2) creates a potential tripartite food web among bacteria, nematodes, and fungi, as hypothesized by Barron (1977). 

Metagenomic approaches have been used to study metabolites produced by bacterial symbionts of marine animals, insects, and nematodes. The literature now provides several examples where DNA-based strategies targeting specific genetic loci have enabled the isolation and cloning of biosynthetic gene clusters encoding for the biosynthesis of important symbiont-associated molecules such as pederin, onn amide A, bryostatins, trunkamide, theopalauamide, and the patellamides. These studies are the focus of another chapter in this series and therefore will not be discussed here. 

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