The plcR regulon is involved in the opportunistic properties of Bacillus thuringiensis and Bacillus cereus in mice and insects.
Bacillus thuringiensis has been widely used for 40 years as a safe biopesticide for controlling agricultural pests and mosquitoes because it produces insecticidal crystal proteins. However, spores have also been shown to contribute to overall entomopathogenicity. Here, the opportunistic properties of acrystalliferous B. thuringiensis Cry(-) and Bacillus cereus strains were investigated in an insect species, Galleria mellonella, and in a mammal, BALB/c mice. In both animal models, the pathogenicity of the two bacterial species was similar. Mutant strains were constructed in which the plcR gene, encoding a pleiotropic regulator of extracellular factors, was disrupted. In larvae, co-ingestion of 10(6) spores of the parental strain with a sublethal concentration of Cry1C toxin caused 70% mortality whereas only 7% mortality was recorded if spores of the DeltaplcR mutant strain were used. In mice, nasal instillation of 10(8) spores of the parental strain caused 100% mortality whereas instillation with the same number of DeltaplcR strain spores caused much lower or no mortality. Similar effects were obtained if vegetative cells were used instead of spores. The cause of death is unknown and is unlikely to be due to actual growth of the bacteria in mice. The lesions caused by B. thuringiensis supernatant in infected mice suggested that haemolytic toxins were involved. The cytolytic properties of strains of B. thuringiensis and B. cereus, using sheep, horse and human erythrocytes and G. mellonella haemocytes, were therefore investigated. The level of cytolytic activity is highly reduced in DeltaplcR strains. Together, the results indicate that the pathogenicity of B. thuringiensis strain 407 and B. cereus strain ATCC 14579 is controlled by PlcR.
Salamitou
Sylvie
S
Unité de Lutte Biologique, INRA, La Minière, 78285 Guyancourt cedex, France2.|Unité de Biochimie Microbienne, CNRS (URA2172), Institut Pasteur, 25 rue du Docteur Roux, 75724 Paris cedex, France1.
Ramisse
Françoise
F
Centre d'Etudes du Bouchet, Laboratoire de Microbiologie, 91710 Vert-Le-Petit, France3.
Brehélin
Michel
M
Laboratoire de Pathologie Comparée, INRA-CNRS (URA 2209), Université Montpellier II, 34095 Montpellier, France4.
Bourguet
Denis
D
Unité de Lutte Biologique, INRA, La Minière, 78285 Guyancourt cedex, France2.
Gilois
Nathalie
N
Unité de Lutte Biologique, INRA, La Minière, 78285 Guyancourt cedex, France2.
Gominet
Myriam
M
Unité de Biochimie Microbienne, CNRS (URA2172), Institut Pasteur, 25 rue du Docteur Roux, 75724 Paris cedex, France1.
Hernandez
Eric
E
Laboratoire de Biologie, HIA Bégin, 94160 Saint Mandé, France5.
Lereclus
Didier
D
Unité de Lutte Biologique, INRA, La Minière, 78285 Guyancourt cedex, France2.|Unité de Biochimie Microbienne, CNRS (URA2172), Institut Pasteur, 25 rue du Docteur Roux, 75724 Paris cedex, France1.
D000818:Animals; D016863:Bacillaceae Infections / Q000209:etiology*; D001409:Bacillus cereus / Q000235:genetics* / Q000472:pathogenicity*; D001413:Bacillus thuringiensis / Q000235:genetics* / Q000472:pathogenicity*; D001426:Bacterial Proteins; D005260:Female; D005798:Genes, Bacterial; D006461:Hemolysis; D006801:Humans; D066298:In Vitro Techniques; D007915:Lepidoptera / Q000382:microbiology; D051379:Mice; D008807:Mice, Inbred BALB C; D009154:Mutation; D009894:Opportunistic Infections / Q000209:etiology*; D010572:Pest Control, Biological; D018085:Regulon; D013171:Spores, Bacterial; D015534:Trans-Activators / Q000235:genetics*; D014774:Virulence / Q000235:genetics
D001426:Bacterial Proteins; C099480:PlcR protein, Bacillus; D015534:Trans-Activators