True Bugs and their Burkholderia Symbionts
For many insects, including aphids, beneficial symbionts are maternally inherited by offspring before birth, ensuring infection. While beneficial to the insect, this makes experimentation on host and microbe responses during symbiont establishment more challenging. Many true bug species have obligate associations with symbiotic bacteria that are transmitted externally. These systems allow us to introduce the symbiont through the natural route of infection and then monitor the physiological consequences
Our Burkholderia-related research over the last several years has focused on:
- assessing patterns of symbiont-specificity and sharing across four sympatric broad-headed bug (Alydus spp., Megalotomus sp.)
- assaying symbiont diversity in association with squash bugs (Anasa tristis)
- assaying the benefits of these associations
- studying how microbial interactions, both in vitro and in vivo, mediate establishment
- studying whether and how the symbiosis influences the ability of their insect hosts to vector plant pathogens
In the coming years, we are particularly interested in developing assays to study symbiont fitness using the squash bug symbiosis.
Monarch Butterfly Defenses Against Protozoan Parasites
In collaboration with Jaap de Roode, we are exploring how consumption of certain milkweed species, particularly those high in toxic cardenolides, increase monarch butterfly resistance to a natural protozoan parasite, Ophryocystis elektroscirrha. We are exploring three, not mutually exclusive hypotheses:
- that high levels of toxins in protective plants directly kill the parasites;
- that protective plants alter the gut microbiome to a community that inhibits parasite proliferation; or,
- that the plants alter the monarch immune response as to increase protection.
Aphids are host to both beneficial and harmful microbes. Of benefit, aphids harbor, Buchnera aphidicola, an obligate bacterial symbiont, which provides amino acids not available in the aphid diet. Aphids frequently also harbor facultative, symbiotic bacteria that can provide protection against pathogens and parasites. Aphid pathogens include a number of viruses, fungi and bacteria.
Our aphid-related research over the last several years has focused on:
- Studying the benefits and costs of symbiosis
- Characterizing the aphid immune system and other forms of defense by coupling genomic and immunological approaches
- Studying aphid immune and defense responses towards fungal pathogens in the presence and absence of protective facultative symbionts
Some Aphid News
- Emory News Article of the Publication of the Pea Aphid Genome Paper
- Daily Mail Article on the Publication of the Pea Aphid Genome Paper
Bean Beetles and their Microbiomes
In collaboration with Chris Beck (Emory University) and Larry Blumer (Morehouse), we are studying the gut associated microbiome of bean beetles (Callosobruchus maculatus). This work developed first as a project to leverage the use of the bean beetle, an excellent experimental system for undergraduate laboratories, as a tool to introduce students to microbiome research. We will disseminate undergraduate research modules based this work through NSF-funded teacher workshops.
In the coming years our bean beetle research will focus on:
- studying how specific gut microbes facilitate the exclusive feeding of bean beetles on dried beans
- assessing how diet changes influence the structure and function of the microbiome
- using the bean beetle laboratory module to assess the benefits of course-based research experiences for undergraduates.
For more information on bean beetles, see beanbeetles.org
Fungus-Growing Ant Symbiosis
The fungus-growing ant–microbe symbiosis consists of coevolving microbial mutualists and pathogens. The diverse fungal lineages that the ants cultivate are attacked by parasitic fungi in the genus Escovopsis. Highly specific host and parasite adaptations shape the ability of Escovopsis lineages to switch to novel hosts over evolutionary time. Specifically, Escovopsis spp. are attracted to their hosts via chemotaxis. This response is host-specific; Escovopsis spp. grow toward their natural host-cultivars more rapidly than toward other closely-related fungi. Moreover, the cultivated fungi secrete compounds that can suppress Escovopsis growth. These antibiotic defenses are likewise specific; in most interactions, cultivars can inhibit growth of Escovopsis spp. not known to infect them in nature but cannot inhibit isolates of their naturally-infecting pathogens.
Our fungus-growing ant-related research over the last several years has focused on:
- collaborative projects to sequence and annotate ant and fungal genomes
- comparison of Escovopsis with free-living relatives
- comprehensive studies of Escovopsis specificity and host-switching potential
In the coming years, we are interested in leveraging the genomic resources we now have available to study the evolution of Escovopsis.
Invasion of a Symbiosis: Megacopta cribraria and its Bacteria
Megacopta Cribraria, the Kudzu Bug, is a pest of soybeans in Asia. In Japan, the ability of these stinkbugs to utilize soybeans is dictated by what strain of bacterial symbiont the bugs carry. In Fall 2009, these bugs were first found in the United States. They have since spread onto soybeans in several states in the Southeastern United States.
Our Megacopta-related research over the last several years has focused on:
- characterizing the impact of symbiosis on development of these bugs on alternative host plants and in their invasive range.
- assessing the ability of the bugs to maintain symbiont titers when reared on alternative host plants.
- Using transcriptomics, assessing host responses to symbiont presence.
For more information on the Megacopta invasion, visit KudzuBug.org.