An out-of-body experience: the extracellular dimension for the transmission of mutualistic bacteria in insects
Proceedings of the Royal Society B Biological Sciences March 4, 2015 Hassan Salem, Laura Florez, Nicole Gerardo et al. 343 citations
Symbiotic partnerships with beneficial microbes drive many metabolic and defensive adaptations in animals and plants. While intracellular symbionts often show genome erosion and co-evolution with their hosts, the consequences of extracellular lifestyles are less understood despite being widespread and functionally important. Using insect-bacteria symbioses as a model, this review highlights diverse routes of extracellular symbiont transfer, unified by the bacteria's ability to survive outside hosts, imposing different genomic, metabolic, and morphological constraints. The evolutionary implications of transmission routes (intracellular versus extracellular) do not necessarily match those of transmission mode (vertical versus horizontal), a key distinction for understanding genomic and physiological outcomes for both partners.