The genome sequence of the entomopathogenic bacterium Photorhabdus luminescens

Abstract

Photorhabdus luminescens is an enterobacterium that is symbiotic with soil entomopathogenic nematodes and pathogenic to a wide range of insects. P. luminescens promotes its own transmission among susceptible insect populations using its nematode host as vector 1 . 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 allows the bacteria 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. Finally, elimination of competitors allows P. luminescens and the nematode to reassociate specifically before leaving the insect cadaver 2,3 .To better understand this complex life style, we determined the genome sequence of P. luminescens subspecies laumondii strain TT01 4 , a symbiont of the nematode Heterorhabditis bacteriophora isolated on Trinidad and Tobago. RESULTS General featuresStrain TT01 possesses a single circular chromosome of 5,688,987 bp with an average GC content of 42.8%. No plasmid replicon was found.A total of 4,839 protein-coding genes, including 157 pseudogenes, seven complete sets (23S, 5S and 16S) of ribosomal RNA operons and 85 tRNA genes, were predicted ( Fig. 1; Supplementary Table 1 online). Toxins against insectsMore toxin genes were predicted in the P. luminescens genome than in any other bacterial genome sequenced yet. A large number of these toxins may be involved in the killing of a wide variety of insects. Some may act synergistically or use redundancy for 'overkill' 5 , ensuring a quick death of the host. In addition, some may kill insects by interfering with their development. In the TT01 genome, two paralogs, plu4092 and plu4436, encode proteins similar to juvenile hormone esterases (JHEs) of the insect Leptinotarsa decemlineata 6 . Juvenile hormone maintains the insect in a larval state. Its inactivation by JHE allows metamorphosis to proceed. JHEs may be used to trigger the insect endocrine machinery at an inappropriate time and thus represents a promising approach for insect control 7 . These genes are located downstream of highly related orphan genes (plu4093 and plu4437), suggesting a locus duplication.The toxicity of the proteins encoded by these two loci was verified experimentally. Two Escherichia coli clones, containing the recombinant BAC1A02 and BAC8C11, were shown to be toxic toward insects. BAC1A02, which contains the locus plu4093-plu4092, exhibited substantial oral toxicity toward three mosquito species, Aedes aegypti,

Bacterial strategies to overcome insect defences

“…In addition to protein factors, several entomopathogens produce toxic secondary metabolites 50,71 that might either harm the host or out-compete other microorganisms 64 .…”

Mass Production of the Beneficial Nematode Heterorhabditis bacteriophora and Its Bacterial Symbiont Photorhabdus luminescens

“…Research has suggested that a single infective juvenile nematode may carry ten cells of P. luminescens, but only three cells are necessary to cause mortality [22]. Other research shows that P. luminescens produces several biologics that are responsible for bioconversion, protection, and nematode transmission [23][24][25][26][27]. Recent studies indicate that insect colonization is due to protective mechanisms against insect macrophages [28].…”

“…Trehalose, a multifunctional sugar, is utilized because of its abundance within the insect and has been suggested to stabilize characteristics such as luminosity [47,48]. Upon sequencing, Duchaud et al [26] reported that the genome of P. luminescens does encode a trehalose operon consisting of a repressor protein (treR), a trehalose permease (treB) and a trehalose 6-phosphate hydrolase (treC). Presently, the metabolism of trehalose and trehalose 6-phosphate in both phase variants has yet to be described.…”

GriC and GriD Constitute a Carboxylic Acid Reductase Involved in Grixazone Biosynthesis in Streptomyces griseus

“…This suggests that the Nocardia CAR is like a GriC-GriD fusion protein. The computer search predicted that GriC and GriD were functionally related, since GriC and GriD homologues are encoded adjacently on the chromosomes of various bacteria, such as SCO7115-SCO7114 in Streptomyces coelicolor A3(2) [14], thnN-thnO in S. cattleya [8], MAP3493-MAP3494 in Mycobacterium avium [15], STH579-STH578 in Symbiobacterium thermophilum [16], ehpF-ehpG in E. herbicola [7], and Plu3307-Plu3306 in Photorhabdus luminescens [17] (the anterior genes encode GriC homologues and the posterior genes encode GriD homologues). We therefore expected that GriC and GriD would constitute a carboxylic acid reductase (Fig.…”