Photorhabdus luminescens (Bacteria) | BCH-ORGA-SCBD-45861 | Organism | Biosafety Clearing-House


Organism (ORGA)

last updated: 17 Jul 2008
Organism information
Photorhabdus luminescens
Kingdom Bacteria
Phylum Proteobacteria
Class Gammaproteobacteria
Order Enterobacteriales
Family Enterobacteriaceae
Genus Photorhabdus
Species Photorhabdus luminescens
  • Bacteria
Characteristics related to biosafety
It is symbiotic with soil entomopathogenic nematodes of the family Heterorhabditidae and pathogenic to a wide range of insects.
Iron acquisition seems to be of particular importance for the life cycle of P. luminescens, as this bacterium has the largest known set of iron, heme, hemin and siderophore transporters. Within an insect, P. luminescens needs to get access to the available nutrients and has to deal with low-iron conditions. P. luminescens has also been found as an opportunistic pathogen in human wounds.

Iron is essential to most bacteria and is often found at limiting concentrations in soil and water habitats and in eukaryotic hosts. Larval stages of the tobacco hornworm, Manduca sexta, contain a ferritin-type iron binding protein in the hemolymph. One mechanism that bacteria use to acquire iron from eukaryotic hosts is to produce siderophore molecules that have high affinity for iron and form soluble iron complexes to sequester and transfer ferric iron into the bacterial cells. Members of the family Enterobacteriaceae typically produce catechol and hydroxamate siderophores, some of which are considered to be virulence factors that capture iron from its bound form, usually as ferritin, in eukaryotic hosts. Siderophores can also function in antibiosis; i.e., siderophores produced by rhizobacteria can inhibit the growth of pathogenic organisms in the rhizosphere and enhance plant growth.
Additional Information
P. luminescens promotes its own transmission among susceptible insect populations using its nematode host. Upon invasion of the host the bacteria are released directly into the open blood system of the insect. Its life cycle comprises a symbiotic stage in the nematode's gut and a virulent stage in the insect larvae, which it kills through toxemia and septicemia.

After the nematode attacks a prey insect and P. luminescens is released, the bacterium produces a wide variety of virulence factors ensuring rapid insect killing. Bioconversion of the insect cadaver by exoenzymes produced by the bacteria allow the it to multiply and the nematode to reproduce. During this process P. luminescens produces antibiotics to prevent invasion of the insect cadaver by bacterial or fungal competitors and the carcass becomes visibly luminescent due to the bioluminescence of P. luminescens.

Once the infection is established, the insect cadaver is bioconverted into a source of nutrients for both the bacteria and the nematodes. Infective juvenile nematodes subsequently re-acquire the bacteria and leave the insect to infect new hosts.

For genomic information, see References.

The bacteria alone are highly lethal to insect larvae when injected into the hemocoel, with less than 30 P. luminescens cells causing 50% mortality to insect larvae (LD50), but are not pathogenic when ingested by insect larvae.
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