38th Annual Meeting of the Society for Invertebrate Pathology

August 7-11, 2005  Anchorage, Alaska, U.S.A
   

The hemolysin alpha-xenorhabdolysin secreted by pathogenic enterobacteria belongs to a new family of cytotoxins and triggers apoptosis

Fabienne Vigneux1, Alain Givaudan1, Pierre Alain Girard1, Carlos Ribeiro1, Stephen Baghdiguian2 and Michel Brehélin1
1Laboratoire d'Ecologie Microbienne des Insectes Interactions Hôtes-Pathogènes UMR 1133 INRA-Université de Montpellier II, 34090 Montpellier, France
2Institut des Sciences de l'Evolution, UMR 5554, Université de Montpellier II, 34090 Montpellier, France

Xenorhabdus nematophila is a Gram negative bacterium belonging to the family of Enterobacteriaceae, symbiotically associated with the nematode Steinernema carpocapsae (Steinernematidae).This entomopathogenic couple kills insects belonging to numerous species after a potent depression of the immune system. X. nematophila is highly pathogen by itself and is able to escape defence reactions and especially phagocytosis.
The α-Xenorhabdolysin (αX), a toxin with cytolytic activity on insect hemocytes (immunocytes) and haemolytic activity on sheep red blood cells (SRBC), was purified from X. nematophila. Granulocytes, which are the functional equivalent of vertebrate macrophages, were the most susceptible hemocytes to αX, which elicits apoptosis in these insect immunocytes.
Peptide sequencing of this cytotoxin allows us to clone the gene coding for this protein. Its expression in transfected E. coli allows the production of large amounts of this cytotoxin/hemolysin with exactly the same activity on insect hemocytes and SRBC than the lysin purified from X. nematophila broth growth. According to nucleotidic and amino acid sequences, αX cannot be classified in an already known family of cytotoxins but belongs to a new family.
This work gives new insights in the understanding of the bacteria-host relationships.

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