Isolation of naturally associated bacteria of necromenicPristionchusnematodes and fitness consequences

Abstract

SUMMARYNematodes and bacteria are major components of the soil ecosystem. Many nematodes use bacteria for food, whereas others evolved specialized bacterial interactions ranging from mutualism to parasitism. Little is known about the biological mechanisms by which nematode-bacterial interactions are achieved, largely because in the laboratory nematodes are often cultured under artificial conditions. We investigated the bacterial interactions of nematodes from the genus Pristionchus that have a strong association with scarab beetles. Pristionchus has a different feeding strategy than Caenorhabditis and meta-genomic 16S sequence analysis of Pristionchus individuals showed a diversity of living bacteria within the nematode gut and on the nematode cuticle. Twenty-three different bacterial strains were isolated from three Pristionchus-beetle associations and were used to study nematode-bacterial interactions under controlled laboratory conditions. We show a continuum of bacterial interactions from dissemination, to reduction in brood size and nematode mortality caused by bacteria derived from insect hosts. Olfactory discrimination experiments show distinct chemoattraction and fitness profiles of Pristionchus nematodes when exposed to different bacteria. For example, Pristionchus pacificus avoids Serratia marcescens possibly because of pathogenicity. Also, P. pacificus avoids Bacillus thuringiensis and insect pathogenic bacteria but is resistant to the human pathogens Staphylococcus aureus and Pseudomonas aeruginosa, unlike Caenorhabditis elegans. Pristionchus specifically recognize and respond to bacteria that cause ill health. Bringing the nematode-bacterial interaction into the laboratory allows detailed functional studies, including the genetic manipulation of the interaction in both nematodes and bacteria.Supplementary material available online at

Adaptive value of a predatory mouth-form in a dimorphic nematode

“…These environments are rich and dynamic, being rapidly colonized by various bacteria [22], fungi and other nematodes [23]. Consistent with conditional regulation in response to such an environment, the dimorphism of P. pacificus is influenced by signals that indicate resource availability.…”

“…B 281: 20141334 brood size reflects starvation-induced shrinkage of the germline, presumably to divert nutrition to the few developing eggs produced [38]. In the wild, however, it is more likely that P. pacificus encounters both bacterial and animal food sources [22,23], albeit in variable abundances. Consequently, assays of reproductive recovery when fed with prey followed by bacteria indicate a fitness benefit for the Eu form on a heterogeneous food resource.…”

Molecular and morphological characterization of Pristionchus pacificus (Nematoda: Rhabditida: Neodiplogastridae), a new record of an entomophilic nematode from Iran

“…Pristionchus species have an interesting necromenic association with scarab beetles. In this relationship, infective juveniles after invading a suitable host, do not feed until after host death at which time they then feed on bacteria, fungi, and other nematodes growing on the insect carcass (Rae et al 2008;Weller et al 2010;Morgan et al 2011). Pristionchus has several species with a necromenic association including P. pacificus that is found on more than ten beetle species including the Oriental beetle Exomala orientalis (Waterhouse, 1875).…”

“…The majority of Pristionchus species associated with beetles show high specificity to a particular beetle species. For example, two common European species, Pristionchus maupasi (Potts, 1910) Paramonov, 1952and P. entomophagus Steiner, 1929 are found on cockchafers (Melolontha F., 1775) and dung beetle (Geotrupes Latreille, 1796), respectively Hong et al 2008a;Rae et al 2008;Morgan et al 2011).…”

“…This species is a satellite model nematode which used in evolutionary and developmental studies like another model species, Caeonorhabditis elegans (Maupas, 1900) (Rudel et al 2005;Hong & Sommer 2006;Herrmann et al 2007;Zauner et al 2007;Click et al 2009). P. pacificus has worldwide distribution and by now, more than 150 isolates have been recovered from soil and scarab beetles in different continents Rae et al 2008;Kanzaki et al 2011).…”