Infection of Tribolium castaneum with Bacillus thuringiensis: Quantification of bacterial replication within cadavers, transmission via cannibalism, and inhibition of spore germination Journal Article


Author(s): Milutinović, Barbara; Höfling, Christina; Futo, Momir; Scharsack, Jörn P; Kurtz, Joachim
Article Title: Infection of Tribolium castaneum with Bacillus thuringiensis: Quantification of bacterial replication within cadavers, transmission via cannibalism, and inhibition of spore germination
Affiliation
Abstract: Reproduction within a host and transmission to the next host are crucial for the virulence and fitness of pathogens. Nevertheless, basic knowledge about such parameters is often missing from the literature, even for well-studied bacteria, such as Bacillus thuringiensis, an endospore-forming insect pathogen, which infects its hosts via the oral route. To characterize bacterial replication success, we made use of an experimental oral infection system for the red flour beetle Tribolium castaneum and developed a flow cytometric assay for the quantification of both spore ingestion by the individual beetle larvae and the resulting spore load after bacterial replication and resporulation within cadavers. On average, spore numbers increased 460-fold, showing that Bacillus thuringiensis grows and replicates successfully in insect cadavers. By inoculating cadaver-derived spores and spores from bacterial stock cultures into nutrient medium, we next investigated outgrowth characteristics of vegetative cells and found that cadaver- derived bacteria showed reduced growth compared to bacteria from the stock cultures. Interestingly, this reduced growth was a consequence of inhibited spore germination, probably originating from the host and resulting in reduced host mortality in subsequent infections by cadaver-derived spores. Nevertheless, we further showed that Bacillus thuringiensis transmission was possible via larval cannibalism when no other food was offered. These results contribute to our understanding of the ecology of Bacillus thuringiensis as an insect pathogen.
Keywords: Bacteria; Bacillus thuringiensis; Cultivation; Pathogens; Bacterial replication; Bacterial stocks; Insect pathogens; Nutrient medium; Red flour beetles; Spore germination; Vegetative cells; Bacteriology
Journal Title: Applied and Environmental Microbiology
Volume: 81
Issue 23
ISSN: 1098-5336
Publisher: American Society for Microbiology  
Date Published: 2015-01-01
Start Page: 8135
End Page: 8144
Sponsor: This work was funded by the German Science Foundation (Deutsche Forschungsgemeinschaft) grant DFG-KU 1929/4-1 within the priority program SPP 1399 Host-Parasite Coevolution.
URL:
DOI: 10.1128/AEM.02051-15
Notes: We thank the members of the Bacillus cluster within this Deutsche Forschungsgemeinschaft priority program for inspiring discussions. We further thank the anonymous reviewers whose valuable suggestions sig- nificantly improved the manuscript.
Open access: yes (repository)