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      Defense contracts: molecular protection in insect-microbe symbioses

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          Abstract

          Insects frequently host microbes that produce defensive molecules: a successful protective strategy and also an opportunity for antibiotic discovery

          Abstract

          Insects cope with environmental threats using a broad array of strategies. A key strategy, widespread among insects but unappreciated until recently, is the use of molecular defenses from symbiotic microbes. Insect-microbe defensive symbioses span the diversity of insect lineages and microbial partners and use molecules ranging from reactive oxygen species to small molecules to protein toxins to defend against predators, parasites, and microbial pathogens. These systems have a strong initial track record as sources of novel biologically active compounds with therapeutic potential. This review surveys the molecular basis for insect-microbe defensive symbioses with a focus on the ecological contexts for defense and on emerging lessons about molecular diversity from bacterial genomes.

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          Most cited references103

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          Multiorganismal insects: diversity and function of resident microorganisms.

          All insects are colonized by microorganisms on the insect exoskeleton, in the gut and hemocoel, and within insect cells. The insect microbiota is generally different from microorganisms in the external environment, including ingested food. Specifically, certain microbial taxa are favored by the conditions and resources in the insect habitat, by their tolerance of insect immunity, and by specific mechanisms for their transmission. The resident microorganisms can promote insect fitness by contributing to nutrition, especially by providing essential amino acids, B vitamins, and, for fungal partners, sterols. Some microorganisms protect their insect hosts against pathogens, parasitoids, and other parasites by synthesizing specific toxins or modifying the insect immune system. Priorities for future research include elucidation of microbial contributions to detoxification, especially of plant allelochemicals in phytophagous insects, and resistance to pathogens; as well as their role in among-insect communication; and the potential value of manipulation of the microbiota to control insect pests.
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            Facultative bacterial symbionts in aphids confer resistance to parasitic wasps.

            Symbiotic relationships between animals and microorganisms are common in nature, yet the factors controlling the abundance and distributions of symbionts are mostly unknown. Aphids have an obligate association with the bacterium Buchnera aphidicola (the primary symbiont) that has been shown to contribute directly to aphid fitness. In addition, aphids sometimes harbor other vertically transmitted bacteria (secondary symbionts), for which few benefits of infection have been previously documented. We carried out experiments to determine the consequences of these facultative symbioses in Acyrthosiphon pisum (the pea aphid) for vulnerability of the aphid host to a hymenopteran parasitoid, Aphidius ervi, a major natural enemy in field populations. Our results show that, in a controlled genetic background, infection confers resistance to parasitoid attack by causing high mortality of developing parasitoid larvae. Compared with uninfected controls, experimentally infected aphids were as likely to be attacked by ovipositing parasitoids but less likely to support parasitoid development. This strong interaction between a symbiotic bacterium and a host natural enemy provides a mechanism for the persistence and spread of symbiotic bacteria.
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              Nutritional interactions in insect-microbial symbioses: aphids and their symbiotic bacteria Buchnera.

              A Douglas (1998)
              Most aphids possess intracellular bacteria of the genus Buchnera. The bacteria are transmitted vertically via the aphid ovary, and the association is obligate for both partners: Bacteria-free aphids grow poorly and produce few or no offspring, and Buchnera are both unknown apart from aphids and apparently unculturable. The symbiosis has a nutritional basis. Specifically, bacterial provisioning of essential amino acids has been demonstrated. Nitrogen recycling, however, is not quantitatively important to the nutrition of aphid species studied, and there is strong evidence against bacterial involvement in the lipid and sterol nutrition of aphids. Buchnera have been implicated in various non-nutritional functions. Of these, just one has strong experimental support: promotion of aphid transmission of circulative viruses. It is argued that strong parallels may exist between the nutritional interactions (including the underlying mechanisms) in the aphid-Buchnera association and other insect symbioses with intracellular microorganisms.
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                Author and article information

                Journal
                CSRVBR
                Chemical Society Reviews
                Chem. Soc. Rev.
                Royal Society of Chemistry (RSC)
                0306-0012
                1460-4744
                2018
                2018
                :
                :
                Article
                10.1039/C7CS00340D
                28745342
                4dda839e-9282-46a8-8ae4-b4fd74a68c91
                © 2018

                http://rsc.li/journals-terms-of-use

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