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Applied and Environmental Microbiology, June 2001, p. 2515-2525, Vol. 67, No. 6
Laboratoire EMIP, Université
Montpellier II, IFR 56, Institut National de la Recherche
Agronomique (UMR 1133), 34095 Montpellier Cedex 05, France
Received 2 January 2001/Accepted 21 March 2001
Xenorhabdus spp. and Photorhabdus spp. are
major insect bacterial pathogens symbiotically associated with
nematodes. These bacteria are transported by their nematode hosts into
the hemocoel of the insect prey, where they proliferate within
hemolymph. In this work we report that wild strains belonging to
different species of both genera are able to produce hemolysin activity
on blood agar plates. Using a hemocyte monolayer bioassay, cytolytic
activity against immunocompetent cells from the hemolymph of
Spodoptera littoralis (Lepidoptera: Noctuidae) was found
only in supernatants of Xenorhabdus; none was detected in
supernatants of various strains of Photorhabdus. During in
vitro bacterial growth of Xenorhabdus nematophila F1, two
successive bursts of cytolytic activity were detected. The first
extracellular cytolytic activity occurred when bacterial cells reached
the stationary phase. It also displayed a hemolytic activity on sheep
red blood cells, and it was heat labile. Among insect hemocyte types,
granulocytes were the preferred target. Lysis of hemocytes by necrosis
was preceded by a dramatic vacuolization of the cells. In contrast the
second burst of cytolytic activity occurred late during stationary
phase and caused hemolysis of rabbit red blood cells, and insect
plasmatocytes were the preferred target. This second activity is heat
resistant and produced shrinkage and necrosis of hemocytes. Insertional
inactivation of flhD gene in X. nematophila
leads to the loss of hemolysis activity on sheep red blood cells and an
attenuated virulence phenotype in S. littoralis (A. Givaudan and A. Lanois, J. Bacteriol. 182:107-115, 2000). This mutant
was unable to produce the early cytolytic activity, but it always
displayed the late cytolytic effect, preferably active on
plasmatocytes. Thus, X. nematophila produced two
independent cytolytic activities against different insect cell targets
known for their major role in cellular immunity.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.6.2515-2525.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Two Distinct Hemolytic Activities in
Xenorhabdus nematophila Are Active against Immunocompetent
Insect Cells

*
Corresponding author. Mailing address: Laboratoire de
Pathologie Comparée (EMIP), Université Montpellier II, INRA
(UMR 1133), CP101, Place E. Bataillon, 34095 Montpellier Cedex 05, France. Phone: (33) 4 67 14 48 12. Fax: (33) 4 67 14 46 79. E-mail:
givaudan{at}crit.univ-montp2.fr.
Present address: Universidade dos Açores, Departmento de
Biologia, Secção de Biologia Celular e Molecular, 9501-801 Ponta Delgada (Açores) Codex, Portugal.
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