Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 12, 2003
Publication Date: August 1, 2003
Citation: Ciche, T., Blackburn, M.B., Ensign, J. 2003. The role of photobactin, a siderophore produced by photohabdus luminescens nc19, in symbiosis with the nematode heterorhabditis bacteriophora and insect pathogenesis. Applied and Environmental Microbiology. Issue # 69 Pg. 4706-4713.
Interpretive Summary: An iron-binding chemical compound, called a siderophore, and the genes responsible for production of the compound were identified from the insect killing bacterium Photorhabdus luminescens, which lives in the gut of certain nematodes that attack insects. Siderophores help certain bacteria acquire iron from their environment. Similar compounds are required by some disease-causing bacteria for infection. When the genes responsible for the production of the siderophore in Photorhabdus were disrupted, the bacteria were incapable of growing in iron-depleted growth medium, however, the bacteria were fully capable of causing disease in insects, and associated normally with their nematode host. The results demonstrate that the iron-binding compound is not critical for the bacteria to cause disease in insects, and does not appear to be involved with growth or reproduction of the nematode. The results of this study will be useful to scientists studying how Photorhabdus infects and kills insects.
Photorhabdus luminescens is a symbiont of the nematode Heterorhabditis bacteriophora and is also a pathogen to many insect larvae. The nematode acts primarily as vector to deliver P. luminescens into insect hosts. The nematode requires the bacteria for insect pathogenicity and as a substrate for growth and reproduction. The ngrA gene, which encodes a putative 4'-phosphopantetheinyl (Ppant) transferase, is required for P. luminescens cells to support nematode growth and reproduction and to produce siderophore and antibiotic activities (Ciche et al., J. Bacteriol.). We sought to determine the role of the siderophore in the interactions of P. luminescens with nematodes and insects by characterizing a mutant unable to produce siderophore. A transposon-induced mutant of P. luminescens, NS414, producing no detectable siderophore activity was obtained. The transposon was inserted into a gene, phbH, which is homologous to peptidyl carrier protein (PCP) domains of nonribosomal peptide synthetases. Cells of NS414, which produced no siderophore activity, were unable to grow in iron-depleted media, but were normal in supporting nematode growth and reproduction and in pathogenicity for insect larvae. Analysis of DNA in the vicinity of the transposon revealed the presence of seven putative siderophore biosynthesis and four (in) siderophore uptake genes. The putative proteins are most similar to those involved in the production of the Vibrio cholerae siderophore, vibriobactin. The siderophore from P. luminescens was purified and its structure determined.