The genetic basis of phylosymbiosis and microbe-mediated hybrid lethality
Immunology
Microbial Ecology and Applied Microbiology
Final Report Abstract
Phylosymbiosis is the reflection of host phylogeny in its microbial community composition. The central aims of this project were to understand the genetic basis of phylosymbiosis and how these host genes control microbial composition and function in the gut microbiome. Nasonia wasps were selected as the ideal model to answer these questions, because of their many technical advantages. Apart from being well-established genetic systems, they have annotated genomes, and the composition of their gut microbiomes are simple and well-studied. Nasonia wasps are also some of the few hosts to show lethality in interspecific hybrids that has been hypothesized to be microbiome-mediated, and likely associated with members of the bacterial genus Proteus. The aims of the project critically relied on optimization of the in vitro system for rearing gnotobiotic Nasonia and the fluorescent-tagging of Proteus strains. Of the many Proteus strains isolated from the Nasonia gut, we tagged several with a GFP-encoding plasmid, and selected Proteus strain 5M for the gnototbiotic experiments, for its ability to retain the plasmid for several days even in the absence of the selective antibiotic. The existing transwell-based germfree rearing system had to be modified to suit the needs of the current project; this system was originally developed as a powerful tool for the investigation of Nasonia development under sterile conditions. However, this experimental platform had to be modified to be able to conduct the controlled, gnotobiotic experiment with Proteus strain 5M. Unfortunately, bacterial overgrowth in the transwells prevented the Nasonia larvae from developing normally, and none of the modifications attempted could optimize the rearing system for use in the current project. Without overcoming the key limitation of bacterial overgrowth, the transwell-based system could not be used to address aims 1 and 2 of the proposal. One potential alternative is a turbidostat or chemostat-like approach to ensure constant replenishment and dilution of the spent Nasonia rearing medium in the transwells to regulate the bacterial density through the constant fresh medium simulating a chemostat or a turbidostat. This would require the development of a novel microfluidic system that could overcome this limitation and ensure the fulfillment of aims 1 and 2. Because of the premature termination of the project and the technical issues encountered with the primary aims, an additional aim was included that related to the general theme of phylosymbiosis in Nasonia wasps. This aim, which was achieved in collaboration with other researchers in my host lab, looked at patterns of parallel evolution between Nasonia hosts and their viromes. Assembly and annotation of the viral gut metagenomes from different species of Nasonia showed that phylosymbiosis indeed extends to viral members of the gut microbiomes as well.
Publications
- Finer-Scale Phylosymbiosis: Insights from Insect Viromes. MSystems. 2018 Dec 26;3(6):e00131-18
Leigh BA, Bordenstein SR, Brooks AW, Mikaelyan A, Bordenstein SR
(See online at https://doi.org/10.1128/mSystems.00131-18)
