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RESEARCH INTERESTS
Evolution of insect-bacterial associations
Microbial diversity; ecology and evolution of symbiosis
Mechanisms of interaction between insects and bacteria
Genome evolution in host-associated bacteria
PUBLICATIONS
According to the Serial Endosymbiosis Theory (SET), eukaryotic cells emerged on our planet some 2.1-2.6 billion years ago as a result of the cellular fusion of two or more prokaryotes. Although this event represents the defining example of a mutualistic endosymbiosis, we find that cooperation between prokaryotes and eukaryotes is quite common in the natural world.
In the Dale lab, we focus on endosymbiotic relationships between bacteria and insects. Insects from a wide range of taxa are known to harbor maternally-transmitted bacterial endosymbionts. In simple terms, the insect benefits from the acquisition of factors (usually nutrients) that can only be provided by the bacterial partner. The bacteria benefit from the opportunity to live in a nutrient-rich niche, free from competition. Insects that harbor these mutualistic endosymbionts are often capable of exploiting nutritionally incomplete diets, because their bacterial endosymbionts provide the missing essential dietary factors. We often regard these insects as pests because they have acquired the ability to persist solely on an unusual diet such as blood or plant phloem. However, in the lab, we also regard these insects as models for study, to understand the nature and diversity of interactions between hosts and their endosymbionts. Projects in the lab often utilize a wide range of techniques to answer scientific questions. These include molecular evolutionary analyses, classical microbial genetics and experimental infections. Three major research themes are currently under investigation in the lab:
i. Common molecular mechanisms of parasitism and mutualism. Parasitic bacteria are known to utilize specialized "virulence" mechanisms to interact with hosts. In many cases, mutualists appear to use the same machinery to facilitate and maintain their intracellular association with hosts! Does this mean that mutualists evolve from parasites? It does seem likely, but how is the function of the virulence machinery attenuated to facilitate mutualism rather than parasitism?
ii. Managing the symbiosis. The insect host and its bacterial partner have to carefully coordinate their activities to maintain favorable conditions for coexistence. In other words, certain things have to happen at certain times to maintain a viable and fruitful association. The bacterial endosymbiont has to contend with a number of factors including the insect immune system and the insect developmental cycle. This requires communication or signaling between the bacterium and host and between members of the bacterial community. How are these signals mediated on a molecular level and what is their outcome?
iii. Genome evolution in bacterial endosymbionts. It turns out that bacteria are not well equipped for a life of isolation in the cells of a eukaryotic host. Although we don't tend to think of bacteria as having a sexual or social nature, these organisms do seem to rely upon genetic exchange to maintain genome integrity. In the absence of opportunities for gene acquisition, host-restricted bacteria tend to lose genes and accumulate deleterious mutations. Over the course of 200 million years of evolution in isolation, bacteria can lose up to 90% of their genetic material. How can we understand the processes that mediate such striking degenerative evolution? To answer this question, we are studying the genomes of endosymbionts that have only recently developed intracellular associations with insect hosts.
Selected Publications:
Pontes, M.H., Babst, M., Lochhead, R., Oakeson, K., Smith, K., and Dale, C. 2008. Quorum sensing primes the oxidative stress response in the insect endosymbiont, Sodalis glossinidius. PLoS ONE. 3(10): e3541.
Dale, C. and Moran, N.A. 2006. Molecular interactions between bacterial symbionts and their hosts. Cell 126, 453-465.
Pontes M.H. and Dale, C. 2006. Culture and manipulation of insect facultative symbionts. Trends in Microbiology 14, 406-412.
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