Photorhabdus luminescens

Classification

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.

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.

Author

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