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Bacillus thuringiensis Spores and Vegetative Bacteria: Infection Capacity and Role of the Virulence Regulon PlcR Following Intrahaemocoel Injection of Galleria mellonella

Micalis Institute, INRA, AgroParisTech, Université Paris-Saclay, 78350 Jouy-en-Josas, France
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These authors contributed equally to this work.
Insects 2019, 10(5), 129; https://doi.org/10.3390/insects10050129
Received: 19 March 2019 / Revised: 19 April 2019 / Accepted: 30 April 2019 / Published: 5 May 2019
(This article belongs to the Special Issue Mechanisms Underlying Transmission of Insect Pathogens)
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Abstract

Bacillus thuringiensis is an invertebrate pathogen that produces insecticidal crystal toxins acting on the intestinal barrier. In the Galleria mellonella larvae infection model, toxins from the PlcR virulence regulon contribute to pathogenicity by the oral route. While B. thuringiensis is principally an oral pathogen, bacteria may also reach the insect haemocoel following injury of the cuticle. Here, we address the question of spore virulence as compared to vegetative cells when the wild-type Bt407cry- strain and its isogenic ∆plcR mutant are inoculated directly into G. mellonella haemocoel. Mortality dose-response curves were constructed at 25 and 37 °C using spores or vegetative cell inocula, and the 50% lethal dose (LD50) in all infection conditions was determined after 48 h of infection. Our findings show that (i) the LD50 is lower for spores than for vegetative cells for both strains, while the temperature has no significant influence, and (ii) the ∆plcR mutant is four to six times less virulent than the wild-type strain in all infection conditions. Our results suggest that the environmental resistant spores are the most infecting form in haemocoel and that the PlcR virulence regulon plays an important role in toxicity when reaching the haemocoel from the cuticle and not only following ingestion. View Full-Text
Keywords: Bacillus thuringiensis; Galleria mellonella; haemocoel; spores; virulence; bio-pesticide; PlcR-regulon Bacillus thuringiensis; Galleria mellonella; haemocoel; spores; virulence; bio-pesticide; PlcR-regulon
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Buisson, C.; Gohar, M.; Huillet, E.; Nielsen-LeRoux, C. Bacillus thuringiensis Spores and Vegetative Bacteria: Infection Capacity and Role of the Virulence Regulon PlcR Following Intrahaemocoel Injection of Galleria mellonella. Insects 2019, 10, 129.

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