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Adaptation of entomopathogenic bacteria to antimicrobial peptides produced by their hosts

How do insect pathogenic bacteria cope with antimicrobial peptides in host?

Antimicrobial peptides (AMPs) are one of the keys to the innate response of the host defense. Resistance to these defense molecules is now recognized as an important virulence phenotype in many human pathogenic bacteria. However, the involvement of resistance to antimicrobial peptides (AMPs) in the virulence of pathogenic bacteria in the insect remained unknown. Following infection, the PAMs are synthesized by the fat body of the insect and are found in the hemolymph few hours after injection. However Photorhabdus, but also Gram-positive bacterium Bacillus thuringiensis is growing rapidly (48 hours) in the hemolymph (blood system) leading to death from sepsis. One of the questions we ask is "How do these pathogens overcome or circumvent the immune system of the host invertebrate"? Seminars organized by the "sustainable interaction” and "Immuninv" networks with our colleagues working on the interactions between B. thuringiensis-insects (Lereclus D. and C. Nielsen-Leroux, La Minière, INRA) and Vibrio splendidus -Crassostrea gigas (oyster variety) (D. Destoumieux-Garzon, RIME, CNRS-UM2) highlighted that the same questions arise in other bacteria-invertebrate interaction systems. The main results are:

  • In the insect model, Drosophila, we showed that the recognition of Xenorhabdus and Photorhabdus by the immune system of the fly is controlled by the Imd signaling pathway that in turn leads to the induction of the synthesis of PAMs (Aymeric et al., 2010).
  • In order to resist to antimicrobials, Photorhabdus and Bacillus thuringiensis change their bacterial envelopes by reducing the net charge, which allows a better resistance to cationic PAMs produced by the insect. By mutagenesis and the monitoring of gene expression in vitro and in vivo, we showed that the dlt operon in Bacillus cereus is involved in the resistance to various anti-bacterial cationic antimicrobial peptides, the lysozyme and the cecropin B from Spodoptera frugiperda (Abi Khattar, 2009; Abi Khattar et al., 2009).

Moreover, we have shown in Spodoptera frugiperda that the expression of cecropins is variable depending on the entomopathogenic bacterium used. Also, we showed that bacteria of the genus Xenorhabdus have developed different strategies to circumvent humoral defense mechanisms of insects either by increasing resistance to antimicrobial peptides, or by preventing their expression (Duvic et al., 2012).

See also

ABI KHATTAR Z, REJASSE A, DESTOUMIEUX-GARZON D, ESCOUBAS JM, SANCHIS V, LERECLUS D, GIVAUDAN A, KALLASSY M, NIELSEN-LEROUX C, GAUDRIAULT S. 2009. The dlt operon of Bacillus cereus is required for resistance to cationic antimicrobial peptides and for virulence in insects. J Bacteriol. 191:7063-7073.

AYMERIC JL, GIVAUDAN A, DUVIC B. 2010. Imd pathway is involved in the interaction of Drosophila melanogaster with the entomopathogenic bacteria, Xenorhabdus nematophila and Photorhabdus luminescens. Mol Immunol. 47:2342-2348.

DUVIC B, JOUAN V, ESSA N., GIRARD PA, PAGES S, ABI KHATTAR Z, VOLKOFF AN, GIVAUDAN A, DESTOUMIEUX-GARZON D, ESCOUBAS JM. 2012. Cecropins as a marker of Spodoptera frugiperda immunosuppression during entomopathogenic bacterial challenge. J Insect Physiol. 58:881-888.

NIELSEN-LEROUX C, GAUDRIAULT S, RAMARAO N, LERECLUS D, GIVAUDAN A. 2012. How the insect pathogen bacteria Bacillus thuringiensis and Xenorhabdus/Photorhabdus occupy their hosts. Curr Opin Microbiol. 15:220-231.