Variation in the Effectors of the Type III Secretion System among
            <i>Photorhabdus</i>
            Species as Revealed by Genomic Analysis

Brugirard-Ricaud, Karine; Givaudan, Alain; Parkhill, Julian; Boemare, Noël; Kunst, Frank; Zumbihl, Robert; Duchaud, Éric

doi:10.1128/jb.186.13.4376-4381.2004

Cited by 51 publications

(40 citation statements)

References 30 publications

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“…In addition, the X. nematophila genome lacks homologs encoding a nonflagellar type III secretion apparatus (9). These facts suggest that XlpA is secreted through the flagellar type III-like secretion apparatus.…”

Section: Resultsmentioning

confidence: 87%

Xenorhabdus nematophila lrhAIs Necessary for Motility, Lipase Activity, Toxin Expression, and Virulence inManduca sextaInsects

et al. 2008

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The gram-negative insect pathogen Xenorhabdus nematophila possesses potential virulence factors including an assortment of toxins, degradative enzymes, and regulators of these compounds. Here, we describe the lysR-like homolog A (lrhA) gene, a gene required by X. nematophila for full virulence in Manduca sexta insects. In several other gram-negative bacteria, LrhA homologs are transcriptional regulators involved in the expression (typically repression) of virulence factors. Based on phenotypic and genetic evidence, we report that X. nematophila LrhA has a positive effect on transcription and expression of certain potential virulence factors, including a toxin subunit-encoding gene, xptD1. Furthermore, an lrhA mutant lacks in vitro lipase activity and has reduced swimming motility compared to its wild-type parent. Quantitative PCR revealed that transcript levels of flagellar genes, a lipase gene, and xptD1 were significantly lower in the lrhA mutant than in the wild type. In addition, lrhA itself is positively regulated by the global regulator Lrp. This work establishes a role for LrhA as a vital component of a regulatory hierarchy necessary for X. nematophila pathogenesis and expression of surface-localized and secreted factors. Future research is aimed at identifying and characterizing virulence factors within the LrhA regulon.

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Section: Resultsmentioning

confidence: 87%

Xenorhabdus nematophila lrhAIs Necessary for Motility, Lipase Activity, Toxin Expression, and Virulence inManduca sextaInsects

et al. 2008

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“…It is well documented that Photorhabdus is armed with a variety of pathogenicity factors and toxins, many of which interfere with host immune defenses (ffrench-Constant et al, 2007). For example, the P. luminescens genome encodes a type III secretion system (TTSS), and one of the effectors, LopT (similar to the YopT effector secreted by Yersinia pestis), represses nodule formation and prevents phagocytosis in Spodoptera littoralis and Locusta migratoria (Brugirard-Ricaud et al, 2004;Brugirard-Ricaud et al, 2005). Our results further suggest that P. luminescens TT01 produces anti-spreading factors, which may have direct pathological effects on M. sexta hemocytes.…”

Section: Discussionmentioning

confidence: 99%

Plasmatocyte-spreading peptide (PSP) plays a central role in insect cellular immune defenses against bacterial infection

Eleftherianos

Yadi

et al. 2009

Journal of Experimental Biology

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SUMMARYInsect hemocytes (blood cells) are a central part of the insect's cellular response to bacterial pathogens, and these specialist cells can both recognize and engulf bacteria. During this process, hemocytes undergo poorly characterized changes in adhesiveness. Previously, a peptide termed plasmatocyte-spreading peptide (PSP), which induces the adhesion and spreading of plasmatocytes on foreign surfaces, has been identified in lepidopteran insects. Here, we investigate the function of this peptide in the moth Manduca sexta using RNA interference (RNAi) to prevent expression of the precursor protein proPSP. We show that infection with the insect-specific bacterial pathogen Photorhabdus luminescens and non-pathogenic Escherichia coli induces proPSP mRNA transcription in the insect fat body but not in hemocytes; subsequently, proPSP protein can be detected in cell-free hemolymph. We used RNAi to silence this upregulation of proPSP and found that the knock-down insects succumbed faster to infection with P. luminescens, but not E. coli. RNAi-treated insects infected with E. coli showed a reduction in the number of circulating hemocytes and higher bacterial growth in hemolymph as well as a reduction in overall cellular immune function compared with infected controls. Interestingly, RNAi-mediated depletion of proPSP adversely affected the formation of melanotic nodules but had no additional effect on other cellular responses when insects were infected with P. luminescens, indicating that this pathogen employs mechanisms that suppress key cellular immune functions in M. sexta. Our results provide evidence for the central role of PSP in M. sexta cellular defenses against bacterial infections. Supplementary material available online at

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“…In the tsetse fly symbiont, Sodalis glossinidius, for example, two type III secretion systems (TTSS) are present, and at least one is required for invasion of host cells (15,16), as is true of many pathogens, including S. enterica and Y. pestis. A TTSS also appears to underlie infection of host cells by the symbionts of Sitophilus weevils (17) and by Photorhabdus species infecting nematodes (18). Such pathogenicity determinants are often transferred horizontally among enteric bacteria via bacteriophage vectors; these transfers have a role in transforming a nonpathogenic to a pathogenic strain (19)(20)(21).…”

mentioning

confidence: 99%

The players in a mutualistic symbiosis: Insects, bacteria, viruses, and virulence genes

Moran

Degnan

Santos

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

289

271

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Aphids maintain mutualistic symbioses involving consortia of coinherited organisms. All possess a primary endosymbiont, Buchnera, which compensates for dietary deficiencies; many also contain secondary symbionts, such as Hamiltonella defensa, which confers defense against natural enemies. Genome sequences of uncultivable secondary symbionts have been refractory to analysis due to the difficulties of isolating adequate DNA samples. By amplifying DNA from hemolymph of infected pea aphids, we obtained a set of genomic sequences of H. defensa and an associated bacteriophage. H. defensa harbors two type III secretion systems, related to those that mediate host cell entry by enteric pathogens. The phage, called APSE-2, is a close relative of the previously sequenced APSE-1 but contains intact homologs of the gene encoding cytolethal distending toxin (cdtB), which interrupts the eukaryotic cell cycle and which is known from a variety of mammalian pathogens. The cdtB homolog is highly expressed, and its genomic position corresponds to that of a homolog of stx (encoding Shiga-toxin) within APSE-1. APSE-2 genomes were consistently abundant in infected pea aphids, and related phages were found in all tested isolates of H. defensa, from numerous insect species. Based on their ubiquity and abundance, these phages appear to be an obligate component of the H. defensa life cycle. We propose that, in these mutualistic symbionts, phage-borne toxin genes provide defense to the aphid host and are a basis for the observed protection against eukaryotic parasites.Acrythosiphon pisum ͉ Hamiltonella defensa ͉ lamboid phage ͉ aphid ͉ Enterobacteriaceae

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Variation in the Effectors of the Type III Secretion System among Photorhabdus Species as Revealed by Genomic Analysis

Cited by 51 publications

References 30 publications

Xenorhabdus nematophila lrhAIs Necessary for Motility, Lipase Activity, Toxin Expression, and Virulence inManduca sextaInsects

Xenorhabdus nematophila lrhAIs Necessary for Motility, Lipase Activity, Toxin Expression, and Virulence inManduca sextaInsects

Plasmatocyte-spreading peptide (PSP) plays a central role in insect cellular immune defenses against bacterial infection

The players in a mutualistic symbiosis: Insects, bacteria, viruses, and virulence genes

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