Abstract
Photorhabdus luminescens is a nematode-symbiotic, gram negative, bioluminescent bacterium, belonging to the family of Enterobacteriaceae. Recent studies show the importance of this bacterium as an alternative source of insecticides, as well as an emerging human pathogen. Various toxins have been identified and characterized in this bacterium. These toxins are classified into four major groups: the toxin complexes (Tcs), the Photorhabdus insect related (Pir) proteins, the “makes caterpillars floppy” (Mcf) toxins and the Photorhabdus virulence cassettes (PVC); the mechanisms however of toxin secretion are not fully elucidated. Using bioinformatics analysis and comparison against the components of known secretion systems, multiple copies of components of all known secretion systems, except the ones composing a type IV secretion system, were identified throughout the entire genome of the bacterium. This indicates that Photorhabdus luminescens has all the necessary means for the secretion of virulence factors, thus it is capable of establishing a microbial infection.
Highlights
Photorhabdus luminescens is a nematode-symbiotic, gram negative, bioluminescent bacterium, belonging to the family of Enterobacteriaceae
P. luminescens is a nematode-symbiotic bacterium with a complex life cycle
Various toxins have been found in the genome of the bacterium, with both oral and injectible activities. These toxins are categorized into four groups; some of them are part of the pathogenicity islands identified in the P. luminescens genome
Summary
Photorhabdus luminescens is a nematode-symbiotic, gram negative, bioluminescent bacterium, belonging to the family of Enterobacteriaceae. The pathogenicity of the bacterium is the result of the presence of pathogenicity islands on its chromosome In these islands there is a large number of genes that encode for toxins, enzymes, bacteriocins and antibiotics. Genomic islands encode for genes that are responsible for symbiosis and nematode growth Another characteristic of P. luminescens is that it undergoes phase variation [1,3]. Phase I or primary variant is found at the infective juvenile stage of the nematode life cycle. At this point, the bacterium produces dyes, antibiotics, lipases, proteases and bioluminescence (due to the lux operon). The fact that human infections with Photorhabdus species have been stated before in the USA and Australia [7,8], and the similarity of the tc genes of P. luminescens with its corresponding genes from Yersinia pestis [9], the causative agent of plague, can raise some serious questions on the possibility of a new human pathogen emerging
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