For the Insect Pathogen Photorhabdus luminescens , Which End of a Nematode Is Out?

Abstract

The nematode Heterorhabditis bacteriophora is the vector for transmitting the entomopathogenic bacterium Photorhabdus luminescens between insect larvae. The dauer juvenile (DJ) stage nematode selectively retains P. luminescens in its intestine until it releases the bacteria into the hemocoel of an insect host. We report the results of studying the transmission of the bacteria by its nematode vector. Cells of P. luminescens labeled with green fluorescent protein preferentially colonized a region of the DJ intestine immediately behind the basal bulb, extending for various distances toward the anus. Incubation of DJ nematodes in vitro in insect hemolymph induced regurgitation of the bacteria. Following a 30-min lag, the bacteria migrated in a gradual and staggered movement toward and ultimately exited the mouth. This regurgitation reaction was induced by a low-molecular-weight, heat-and protease-stable, anionic component present in arthropod hemolymph and in supernatants from insect cell cultures. Nematodes anesthetized with levamisole or treated with the antihelmenthic agent ivermectin did not release their bacteria into hemolymph. The ability to visualize P. luminescens in the DJ nematode intestine provides the first clues to the mechanism of release of the bacteria during infection of insect larvae. This and the partial characterization of a component of hemolymph triggering release of the bacteria render this fascinating example of both a mutualistic symbiosis and disease transmission amenable to future genetic and molecular study. The mutualistic association of the enteric entomopathogenic bacterium Photorhabdus luminescens and its nematode vectorHeterorhabditis bacteriophora is a potentially useful model for studies of vector-borne disease and use as biological control agents for arthropod vectors of disease and agricultural insect pests. The two partners, acting in concert, are voracious pathogens to a wide variety of insect larvae (24, 28; for a recent review, see reference 15). The dauer juvenile (DJ) stage of the nematode carries in its intestine a monoculture of symbiotic P. luminescens (13,20,21,25). The nematode locates a susceptible insect victim, enters the hemocoel, and releases its charge of bacteria, and death of the insect follows, usually within 24 h (15,24,28). Insect mortality is primarily attributable to the extreme virulence of P. luminescens, where the 50% lethal dose for some insects is less than 30 cells when injected into the hemocoel (24,25,29). The bacteria produce potent orally active insecticidal protein toxins that are being developed as biological control agents (5, 6, 18).During growth inside the insect cadaver, the DJ develops into a reproductively mature adult hermaphrodite. The nematode offspring feed on the P. luminescens cells and are highly specific in requiring their specific strain of P. luminescens for growth and reproduction (1,12,16). Following several rounds of reproduction, lasting approximately 2 weeks and in apparent response to impending nutrient limitation, severa...

Olfaction shapes host–parasite interactions in parasitic nematodes

“…IJs then infect the host either by entering through natural orifices or by penetrating through the insect cuticle (20). Following infection, IJs release a bacterial endosymbiont into the insect host and resume development (21)(22)(23). The bacteria proliferate inside the insect, producing an arsenal of secondary metabolites that lead to rapid insect death and digestion of insect tissues.…”

Drosophila lifespan enhancement by exogenous bacteria

“…However, diet and environment during the animal's life can drastically alter its bacterial population (3)(4)(5). Even though an animal is exposed to a vast array of bacteria, the complexity of fauna in its gut can vary widely, some harboring a single species, others hosting hundreds (6)(7)(8)(9)(10).…”

Visualizing Bacteria in Nematodes using Fluorescent Microscopy

“…Related methods have been described previously to isolate the bacterial symbiont, grow nematodes axenically, and manipulate both partners [25][26][27] . The protocol described here was developed in the Xenorhabdus nematophila-Steinernema carpocapsae model system 14 , and similar approaches have been used in other entomopathogenic nematode-bacterial associations 9,15,17,18 . Several conditions must be met in order to apply this method to other nematode-bacterial systems.…”

“…The methods described were developed to investigate the association between Steinernema carpocapsae and Xenorhabdus nematophila 14 . Similar methods have been used to investigate other nematode-bacterium associations 9,[15][16][17][18] and the approach therefore is generally applicable.…”

“…The methods described were developed to investigate the association between Steinernema carpocapsae and Xenorhabdus nematophila 14 . Similar methods have been used to investigate other nematode-bacterium associations 9,[15][16][17][18] and the approach therefore is generally applicable.The method allows characterization of bacterial presence and localization within nematodes at different stages of development, providing insights into the nature of the association and the process of colonization 14,16,19 . Microscopic analysis reveals both colonization frequency within a population and localization of bacteria to host tissues 14,16,[19][20][21] .…”