Healthcare for insects?
Thursday, October 29th, 2009
Insects are the most abundant and diverse animal class on earth, and they are associated with an amazing variety of symbiotic microorganisms. In fact, mutualistic bacteria probably constitute a key factor for the enormous success of insects in adapting to novel environments and food sources. Several insect taxa completely depend on their mutualistic bacteria for successful growth and reproduction, and the nutrients that are provided by the bacteria have been elucidated in some cases by physiological and/or genomic studies. These nutritional interactions have been the focus of considerable attention, and it is generally assumed that the advantage for the insect in most insect–bacteria symbioses is the supply with nutrients. Recently, however, an increasing number of studies indicate that another type of symbiotic associations can play an equally crucial role: the protection of the insect host or its nutritional resources against pathogens, parasitoids or predators by symbiotic microorganisms. Interestingly, a specific group of bacteria is involved in approximately half of the described defensive symbioses: the high-GC Gram-positive actinobacteria. Why are members of this group so common as defensive mutualists in insects, while they are only very rarely found to be involved in nutritional symbioses? This article argues that actinobacteria are predisposed towards engaging in defensive rather than nutritional interactions owing to their ecological and physiological prerequisites, in particular their ability to exploit a wide range of nutrient sources and their extraordinary potential to produce secondary metabolites with antibiotic properties. A comparison of defensive insect–actinobacteria symbioses known to date yields interesting insights into the conditions under which such associations evolve and points to future directions for research on other insect taxa that might be protected by microorganisms.
Mutualistic microorganisms are well known to play a key role in providing nutrients for successful growth and reproduction in many insects. Several recent studies indicate that they can be equally important for the protection of the host and its nutritional resources against pathogen attack. In particular, different actinobacteria have been found to defend ants, beetles and wasps against detrimental microorganisms by producing antibiotics. The extraordinary abilities of actinobacteria to exploit a wide variety of carbon and nitrogen sources and their extensive repertoire of secondary metabolites probably predispose this group to engage in protective symbioses. Defensive mutualisms with actinobacteria might constitute a general and widespread theme in the ecology and evolution of arthropods, and the study of the secondary metabolites involved promises to uncover novel drug candidates for human medicine.
Actinobacteria as mutualists: general healthcare for insects? Trends Microbiol. Oct 21 2009
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