Work in the lab aims to integrate data from genomes and experiments to determine how complex host interactions shape bacterial evolution and ecology, and how these interactions feedback to impact hosts. We use a variety of systems to address these questions.
Interactions of insects, plants and associated bacteria
Experiments in the lab focus on a tractable system of interactions between the plant-associated Pseudomonas and aphids. Pseudomonads are ubiquitous epiphytic bacteria on plant surfaces. They can also impact hemipteran insect survival and behavior. Hemipteran insects such as aphids are serious agricultural pests and are difficult to control with traditional methods like pesticides. We have found that some pseudomonads are highly pathogenic to aphids, and they can also influence aphid feeding behavior. Projects in the lab focus on the ecological implications of these interactions in agroecosystems, as well as the connections between bacterial genomic evolution and phenotypes, and species interactions.
An exciting discovery from the lab is that aphids avoid Pseudomonas strains by visually detecting bacterial fluorescence. We found that pea aphids avoid feeding on leaves with some strains of epiphytic pseudomonads. Many pseudomonads make compounds such as pyoverdine, a siderophore, that produces a blue-green fluorescence under ultraviolet light. Pyoverdine production can alter the spectrum of reflected light from plants so leaves appear more blue to aphids, causing aphids to avoid them. We are currently working to understand how environmental conditions influence pseudomonad production of pyoverdine and other fluorescent compounds, and how this influences aphid behavior.
We also found that aphids can influence pseudomonads in the phyllosphere. Epiphytic pseudomonads can benefit from sugary aphid waste and grow better when aphids are present on plants. This highlights how understudied interactions between members of phyllosphere communities can have important impacts. To understand this at the community level, we developed a synthetic phyllosphere community of bacterial taxa that we can combine with pseudomonads of interest. Future work will use this community to test how microbe-microbe interactions influence mutlipartite interactions of plants, bacteria, and aphids.
We also found that aphids can influence pseudomonads in the phyllosphere. Epiphytic pseudomonads can benefit from sugary aphid waste and grow better when aphids are present on plants. This highlights how understudied interactions between members of phyllosphere communities can have important impacts. To understand this at the community level, we developed a synthetic phyllosphere community of bacterial taxa that we can combine with pseudomonads of interest. Future work will use this community to test how microbe-microbe interactions influence mutlipartite interactions of plants, bacteria, and aphids.
Bacterial adaptation to the environment
Pseudomonads are a particularly attractive system because they have a high degree of phenotypic and genetic diversity. This makes it possible to use comparative approaches within a phylogenetic framework to connect genetic variation to phenotypic variation, such as for the traits that enable insect infection. The lab is investigating the genetic basis of growth and infection of aphids, as well as epiphytic growth, within pseudomonads. We are also working to understand the role of siderophores in phyllosphere community interactions.
In a project driven by collaboration (with Dr. Rachel Vannette, UC Davis), we examined the processes that drive diversification and the evolution of novelty in host-associated bacteria of the genus Acinetobacter. We used genomics to understand how some Acinetobacter evolved to become specialized for growth in floral nectar and diversified within this novel habitat. We have identified several new species of floral-nectar dwelling Acinetobacter from just our initial sampling and genome sequencing, and using comparative genomics we found one evolutionary origin of floral nectar adaptation in Acinetobacter. In future work, we are investigating specific pathways underlying adaptation to growth in nectar.
In a project driven by collaboration (with Dr. Rachel Vannette, UC Davis), we examined the processes that drive diversification and the evolution of novelty in host-associated bacteria of the genus Acinetobacter. We used genomics to understand how some Acinetobacter evolved to become specialized for growth in floral nectar and diversified within this novel habitat. We have identified several new species of floral-nectar dwelling Acinetobacter from just our initial sampling and genome sequencing, and using comparative genomics we found one evolutionary origin of floral nectar adaptation in Acinetobacter. In future work, we are investigating specific pathways underlying adaptation to growth in nectar.
Symbiont evolution
Symbiont evolution can be greatly influenced by animal hosts, in ways that vary across systems. Work in the lab has shown that the luminous symbionts of deep-sea anglerfish have undergone genomic reduction and appear metabolically dependent on their hosts. This is surprising, because these bacteria are transmitted through the environment. Current work in the lab is asking how host interactions influence the population structure and genetic diversity of luminous symbionts, comparing systems where bacteria are host-dependent with facultative symbionts. This project is collaborative with Dr. Lydia Baker (University of Miami) and Dr. Sara Miller (UMSL).
The lab also focuses on insect-symbiont systems. For instance, burying beetles rear their young on decomposing carcasses and microbial symbionts are partially responsible for preventing putrefaction of the carcass. Studies in the model burying beetle Nicrophorus vespilloides found that yeast symbionts in the genus Yarrowia may be important in this role. Work in the lab is studying the evolution and host specificity of Yarrowia and bacteria associated with diverse burying beetle populations. Broadly, these two projects highlight current interests in the lab: understanding how host populations and environmental symbiont populations interact across geography.
The lab also focuses on insect-symbiont systems. For instance, burying beetles rear their young on decomposing carcasses and microbial symbionts are partially responsible for preventing putrefaction of the carcass. Studies in the model burying beetle Nicrophorus vespilloides found that yeast symbionts in the genus Yarrowia may be important in this role. Work in the lab is studying the evolution and host specificity of Yarrowia and bacteria associated with diverse burying beetle populations. Broadly, these two projects highlight current interests in the lab: understanding how host populations and environmental symbiont populations interact across geography.