Abstract
Experimental infection systems are important for studying antagonistic interactions and coevolution between hosts and their pathogens. The red flour beetle Tribolium castaneum and the spore-forming bacterial insect pathogen Bacillus thuringiensis (Bt) are widely used and tractable model organisms. However, they have not been employed yet as an efficient experimental system to study host-pathogen interactions. We used a high throughput oral infection protocol to infect T. castaneum insects with coleopteran specific B. thuringiensis bv. tenebrionis (Btt) bacteria. We found that larval mortality depends on the dietary spore concentration and on the duration of exposure to the spores. Furthermore, differential susceptibility of larvae from different T. castaneum populations indicates that the host genetic background influences infection success. The recovery of high numbers of infectious spores from the cadavers indicates successful replication of bacteria in the host and suggests that Btt could establish infectious cycles in T. castaneum in nature. We were able to transfer plasmids from Btt to a non-pathogenic but genetically well-characterised Bt strain, which was thereafter able to successfully infect T. castaneum, suggesting that factors residing on the plasmids are important for the virulence of Btt. The availability of a genetically accessible strain will provide an ideal model for more in-depth analyses of pathogenicity factors during oral infections. Combined with the availability of the full genome sequence of T. castaneum, this system will enable analyses of host responses during infection, as well as addressing basic questions concerning host-parasite coevolution.
Highlights
Insects are important model organisms for studying the evolution and mechanisms of immunity and host-pathogen interactions [1,2,3,4]
We analysed the infectivity of four different Bacillus thuringiensis (Bt) strains (Table 1) towards three different T. castaneum populations, the laboratory populations San Bernardino (SB) and Georgia 2 (GA-2) and the recently wild-collected Croatia 1 (Cro1) population (Figure 1A)
The system enables the simultaneous study of bacterial infection strategies and responses of the host in a well-studied insect model organism
Summary
Insects are important model organisms for studying the evolution and mechanisms of immunity and host-pathogen interactions [1,2,3,4]. Experimental approaches have been established for oral inoculation of natural bacterial pathogens for the main insect model, the fruit fly Drosophila melanogaster [5,6,7], thereby adding a vital tool to the methodological repertoire of insect immunology. This has enabled the successful in-depth study of the pathology of bacterial infections [8], [9]. There is a strong interest in research on pest management for this species
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