Microbial Ecology in States of Health and Disease Workshop Summary (2014) / Chapter Skim
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A7 Lessons from studying insect symbioses--Angela E. Douglas
A7 Lessons from studying insect symbioses--Angela E. Douglas
Pages 207-223
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From page 207... ...
The influence of these resident microorganisms on their animal host is profound and operates at two levels: in physiological time, such that the physiology and well-being of the animal is influenced by the composition, density, and activities of colonizing microorganisms; and in evolutionary time, through selection on the magnitude and pattern of the animal response to the infecting microorganisms. We can only understand animal-microbial interactions by combining these physiological and evolutionary perspectives.
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From page 208... ...
Compounding the short life span of many insects, microbes associated with the foregut and hindgut are eliminated at every insect molt (when the cuticle lining these gut regions is shed) , and all microbes are shed when the larval gut is broken down and the adult gut develops during metamorphosis of higher ("holometabolous")
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From page 209... ...
, usually via the eggs in the female ovaries. The resultant perfect congruence between the phylogenies of the microbial symbiont and their insect hosts, in some insect groups over more than 100–200 million years (Dale and Moran, 2006; and Moran et al., 2005)
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From page 210... ...
. The resident gut bacteria induce IMD signaling in the gut epithelial cells, resulting in localization of the NF-κB transcription factor Relish to the epithelial cell nucleus, but, contrary to expectation, the expression of AMPs is not induced (Ryu et al., 2008)
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From page 211... ...
(A) Resident microorganisms in the Drosophila gut activate the IMD pathway, but expression of AMPs is repressed by the transcription factor Caudal.
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From page 212... ...
Further evidence that the innate immune system can serve to promote coexistence between insects and their resident microbiota comes from several studies on intracellular bacteria in bacteriocytes. Although they have much-reduced genomes, these bacteria are predicted to possess the molecular patterns that are recognized by the insect immune system.
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From page 213... ...
. Benefits of the Resident Microbiota to the Host The contribution of the resident microbiota to the well-being of an animal, and the underlying mechanisms, can most readily be investigated by comparing animals experimentally deprived of their microbiota with untreated animals bearing their natural microbial complement.
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From page 214... ...
The same experimental approach, together with complementary metabolic analysis, has been applied to plant sap feeders, revealing that these symbionts provide essential amino acids. The most detailed information is available for the association between the plant phloem sap-feeding pea aphid Acyrthosiphon pisum and its bacteriocyte symbiont Buchnera, for which both genomes are sequenced and annotated (International Aphid Genomics Consortium, 2010; and Shigenobu et al., 2000)
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From page 215... ...
suggests that the microbiota may have a nutritional role in this insect, but this has not been demonstrated definitively. There is unambiguous evidence that specific resident microorganisms promote the resistance of insects to certain natural enemies, including viruses, bacteria, fungi, nematodes, and parasitic wasps.
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From page 216... ...
The second example relates to parasitic wasps, many of which exploit various insects by depositing an egg in the body cavity of their victim. The resultant wasp larva consumes tissues of the living insect over some days, and following the death of the insect, the adult wasp emerges from the dead insect "mummy." The resistance of pea aphids to the parasitic wasp Aphidius ervi is heightened by the presence of the γ-proteobacterium Hamiltonella defensa, which occurs in the body cavity of some pea aphids (the prevalence of H. defensa varies widely among different pea aphid populations)
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From page 217... ...
has received little attention, partly because dependence is often interpreted as evidence for benefit, even in the absence of evidence for any service (e.g., nutrient provisioning, defensive role) , but also because interactions between animal hosts and their resident microbiota are often investigated without considering their evolutionary context.
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From page 218... ...
For example, the genomes of both the pea aphid Acyrthosiphon pisum and its Buchnera symbiont have been sequenced (International Aphid Genomics Consortium, 2010; and Shigenobu et al., 2000) , revealing a large-scale loss in the capacity of Buchnera to synthesize nonessential amino acids (which can be synthesized by the aphid host)
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From page 219... ...
The amino acids produced by each bacterium are made available to both the insect host and the alternative bacterium. Both bacteria require the ten nonessential amino acids from the host.
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From page 220... ...
. Current and Future Lessons from Insect Symbioses Insect symbioses offer various clear-cut exemplars of processes underlying interactions between animals and their resident microbiota.
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From page 221... ...
. Symbiotic bacteria enable insect to use a nutritionally inadequate diet.
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From page 222... ...
. Aphid genome expression reveals hostsymbiont cooperation in the production of amino acids.
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From page 223... ...
. Phylogenetic characterization of two novel commensal bacteria involved with innate immune homeostasis in Drosophila melanogaster.
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