Abstract
Settled on the foundations laid by zoologists and embryologists more than a century ago, the study of symbiosis between prokaryotes and eukaryotes is an expanding field. In this review, we present several models of insect–bacteria symbioses that allow for the detangling of most known features of this distinctive way of living, using a combination of very diverse screening approaches, including molecular, microscopic, and genomic techniques. With the increasing the amount of endosymbiotic bacteria genomes available, it has been possible to develop evolutionary models explaining the changes undergone by these bacteria in their adaptation to the intracellular host environment. The establishment of a given symbiotic system can be a root cause of substantial changes in the partners’ way of life. Furthermore, symbiont replacement and/or the establishment of bacterial consortia are two ways in which the host can exploit its interaction with environmental bacteria for endosymbiotic reinvigoration. The detailed study of diverse and complex symbiotic systems has revealed a great variety of possible final genomic products, frequently below the limit considered compatible with cellular life, and sometimes with unanticipated genomic and population characteristics, raising new questions that need to be addressed in the near future through a wider exploration of new models and empirical observations.
Highlights
In this review we have presented paradigmatic examples of endosymbiotic systems, from the very beginning of the intimate association to the most extreme cases of genome reduction, including the ultimate fate of the endosymbionts once they reach a limit stage of degeneration in which they cannot fulfill the host needs
Despite the huge variability of systems found in nature to date, convergent solutions are achieved in most cases
Bacterial and fungal species from some widely distributed clades living in sympatry with the insect hosts can enter the symbiotic association, and can be used as copartners or even replace the first obligate endosymbiont
Summary
In addition to the two canonical endosymbioses that were the origin of mitochondria and chloroplasts, stable mutualistic associations have evolved frequently and independently in numerous eukaryotes groups [2]. Most of such symbioses have a biochemical basis. Pierantoni and the embryologist Karel Šulc at the beginning of the past century revealed that this type of relationship was widespread in many insect groups [4,5] They recognized the bacteriome (at that time called mycetome) as an organ dedicated to keeping microorganisms inside the insect body. Among the examples presented by him in his seminal book published in English in 1965 [5], some are still being analyzed nowadays, providing new insights on this kind of intimate association, and will be the focus of this review
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call