Ecological relevance and molecular regulation of antibiotic-producing bacterial symbionts in Lagriinae beetles

• Applicant: Professor Dr. Martin Kaltenpoth, since 4/2021
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; Microbial Ecology and Applied Microbiology ; Systematics and Morphology (Zoology)
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 416606594

Symbiotic interactions with microorganisms are a driving force in the evolution of eukaryotes. Along with nutritional symbioses, those with a defensive basis are frequent in nature, yet less is known about their ecology and evolution, especially under natural conditions. Lagriinae beetles engage in a symbiosis with multiple strains of Burkholderia gladioli bacteria, which are transmitted from mother to offspring and can protect the host eggs from antagonistic fungi. Recent findings show that co-existing symbiont strains can each produce a distinct set of bioactive secondary metabolites; at least five in total. Using this model system, our aim is to better understand the ecology, evolution and molecular basis of this defensive symbiosis. The proposal involves two projects, the first one focuses on the ecological relevance of symbiont-mediated defense during host development and across Lagriinae species. Using a combination of antibiotic-biosynthesis gene expression profiling, analytical chemistry, mass-spectrometry imaging, fluorescence in-situ hybridization (FISH) and manipulative assays, we will characterize the dynamics of antibiotic production and assess its importance during the vulnerable molting stages of the insect. Additionally, evaluating the production of these compounds by symbionts from different Lagriinae species will inform on their importance for the evolution of the symbiosis. A second project will investigate the molecular regulation of the defensive symbiosis, considering factors from both host and symbiont that might be determinant for the establishment and maintenance of the association. Transcriptomic data from key time points for host tissue colonization by the symbionts will be compared between symbiotic and symbiont-free beetles, in order to identify a subset of candidate immune genes that are important for symbiont regulation. These will be knocked-down using RNAi on the beetles, and the effect on symbiosis establishment will be assessed using qPCR and FISH. To investigate symbiont traits that are relevant for associating to the insect, random transposon mutagenesis will be used to create a library of symbiont mutants and re-infect symbiont-free beetles. The community of mutants that successfully establishes in the host will be contrasted to the original library to identify genes that are likely crucial for colonizing and surviving in the beetle. Importantly, the genetic repertoire in the recovered mutant library will be compared to the naturally occurring strains, assessing whether the presence or absence of certain genes reflects, and might therefore explain, the prevalence of specific strains. Both projects should contribute to our general understanding of animal-microbe interactions in the context of host protection, and will provide valuable insights on the evolution and stability of multi-strain symbiotic interactions.

• DFG Programme: Research Grants
• Ehemalige Antragstellerin: Dr. Laura V. Florez, until 3/2021