Photorhabdus luminescens

Classification

Figure 1(A) shows the bioluminescence of Photorhabdus luminescens. It was taken with film 72 hours after the bacteria infected Galleria mellonella (waxworms).(Image courtesy Todd Ciche/California Institute of Technology),Figure 1(B) shows GFP-labeled Photorhabdus luminescens in the intestine of the Heterorhabditis bacteriophora nematode.(Image courtesy Todd Ciche,Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824 USA)

Domain: Bacteria, Phylum: Proteobacteria, Class: Gammaproteobacteria, Order: Enterobacteriales, Family: Enterobacteriaceae, Genus: Photorhabdus, Species: luminescens

Species

Photorhabdus luminescens

Description and Significance

Photorhabdus luminescens also known as Xenorhabdus luminescens is a bioluminescent microbe (Figure 1). Bioluminescence is an energy costly process and as yet no good explanation is given for this process. Theories include some unknown biochemical role, a warning to scavenging nocturnal mammals or even that it serves as a lure to temp fresh insect victims into range. The most important function of this microbe is the symbiotic relationship with soil entomopathogenic nematodes of the family Heterorhabditidae and pathogenic to a wide range of insects (Figure 2). When the nematode infects an insect, P. luminescens is released into the blood stream and rapidly kills the insect host (within 48 hours) by producing toxins. It also secretes enzymes which break down the body of the infected insect and convert it into nutrients which can be utilized by both nematode and bacteria. In this way, both organisms gain enough nutrients for further replication and reproduction. P. luminescens is the only organism that is known to exhibit dual phenotype (symbiotic within one insect, and pathogenic in another) (Figure 3).During the process P. luminescens produces antibiotics to prevent invasion of the insect by bacterial or fungal competitors and it becomes visibly luminescent due to the bioluminescence of P. luminescens. There have been number of reported cases of human infection by Photorhabdus luminescens.

Genome Structure

The complete genome sequence of Photorhabdus luminescens, strain TT01 is 5,688,987 base pairs (bp) long and contains 4,839 predicted protein-coding genes (Figure 4). It encodes a large number of adhesins, toxins, hemolysins, proteases and lipases, and contains a wide array of antibiotic synthesizing genes. These proteins play role in the elimination of competitors, host colonization, invasion and bioconversion of the insect cadaver, making P. luminescens a promising model for the study of symbiosis and host-pathogen interactions. Comparison with the genomes of related bacteria reveals the acquisition of virulence factors by extensive horizontal transfer and provides clues about the evolution of an insect pathogen.

Pathogenic functions are encoded within a number of pathogenicity islands (PAIs) contained on the bacterial chromsome. These include a large number of genes that code for secreted toxins and enzymes, as well as genes that encode products for the production of antibiotics and bacteriocins. Secretion of these products occurs by an array of systems including type I, type II, and type III secretion systems. The type III system is closely related to the Yersinia plasmid-encoded type III system. Genes that promote symbiotic relationships are also encoded on genomic islands on the chromosome including some that affect nematode development.

Now that the complete genome has been sequenced, the next challenge is to identify genes involved in symbiosis that could be used to increase the production of the worms for the biological control of insects. In tests, Photorhabdus luminescens reduced Colorado potato beetles and sweet potato whitefly by 100 percent in lab conditions. The potato beetle is notorious for developing resistance to insecticides, so scientists are seeking non-chemical controls as possible natural insecticides.

Cell Structure, Metabolism and Life Cycle

Interesting features of cell structure; how it gains energy; what important molecules it produces.

Ecology and Pathogenesis

Habitat; symbiosis; biogeochemical significance; contributions to environment.
If relevant, how does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.

References

Saux, M. F et al. Polyphasic classification of the genus Photorhabdus and proposal of new taxa: P. luminescens subsp. luminescens subsp. nov., P. luminescens subsp. akhurstii subsp. nov., P. luminescens subsp. laumondii subsp. nov., P. temperata sp. nov., P. temperata subsp. temperata subsp. nov. and P. asymbiotica sp. nov, International Journal of Systematic Bacteriology, 49, 1645-1656 (1999).

Duchaud, E. et al. The genome sequence of the entomopathogenic bacterium Photorhabdus luminescens. Nature Biotechnology 21, 1307-1313 (2003).

Liu, D. et al. Insect resistance conferred by 283-kDa Photorhabdus luminescens protein TcdA in Arabidopsis thaliana. Nature Biotechnology 21, 1222-1228 (2003).

Williamson et al. Sequence of a symbiont. Nature Biotechnology 21, 1294 - 1295 (2003)

Blackburn, M. B. et al. The broadly insecticidal Photorhabdus luminescens toxin complex a (Tca): Activity against the Colorado potato bettle, Leptinotarsa decemlineata, and sweet potato fly Bemisia tabaci, Journal of Insect Science, 1-11 (2005)

http://staff.bath.ac.uk/bssnw/photorhabdus_luminescens.htm

http://www.wormbook.org/chapters/www_genomesHbacteriophora/genomesHbacteriophora.html

http://www.genomenewsnetwork.org/articles/10_03/toxic_glow.shtml

http://www.ebi.ac.uk/2can/genomes/bacteria/Photorhabdus_luminescens.html

Author

Page authored by Ahsan Munir & Brian Charles Mcmillen ,student of Prof. Jay Lennon at Michigan State University.