Hijackers, hitchhikers, or co-drivers? Themysteries of mobilizable genetic elements

PLOS Biology

Manuel Ares-Arroyo, Charles Coluzzi, Jorge A. Moura de Sousa, Eduardo P. C. Rocha*

Abstract

Mobile genetic elements shape microbial gene repertoires and populations. Recent results

reveal that many, possibly most, microbial mobile genetic elements require helpers to transfer between genomes, which we refer to as Hitcher Genetic Elements (hitchers or HGEs). They may be a large fraction of pathogenicity and resistance genomic islands, whose mechanisms of transfer have remained enigmatic for decades. Together with their helper elements and their bacterial hosts, hitchers form tripartite networks of interactions that evolve rapidly within a parasitism–mutualism continuum. In this emerging view of microbial

genomes as communities of mobile genetic elements many questions arise. Which elements

are being moved, by whom, and how? How often are hitchers costly hyper-parasites or beneficial mutualists? What is the evolutionary origin of hitchers? Are there key advantages associated with hitchers’ lifestyle that justify their unexpected abundance? And why are hitchers systematically smaller than their helpers? In this essay, we start answering these questions and point ways ahead for understanding the principles, origin, mechanisms, and impact of hitchers in bacterial ecology and evolution.

More information at DOI: https://doi.org/10.1371/journal.pbio.3002796