9.C.14 The Intercellular Bacterial Nanotube (IBN) Family
Bacteria communicate primarily via secreted extracellular factors. Dubey and Ben-Yehuda (2011) identified a previously uncharacterized type of bacterial communication mediated by nanotubes that bridge neighboring cells. Using Bacillus subtilis, they visualized transfer of cytoplasmic fluorescent molecules between adjacent cells. Additionally, by coculturing strains harboring different antibiotic resistance genes, they demonstrated that molecular exchange enables cells to transiently acquire nonhereditary resistance. Furthermore, nonconjugative plasmids could be transferred from one cell to another, thereby conferring hereditary features to recipient cells. Electron microscopy revealed the existence of variously sized tubular extensions bridging neighboring cells, serving as a route for exchange of intracellular molecules. These nanotubes also formed in an interspecies manner, between B. subtilis and Staphylococcus aureus, and even between B. subtilis and the evolutionary distant bacterium, E. coli. Nanotubes may represent a major form of bacterial communication in nature, providing a network for exchange of cellular molecules within and between species.
Utilizing Bacillus subtilis as a model organism at low cell density, nanotubes are complex, existing as both intercellular tubes and extending tubes, with the latter frequently surrounding the cells in a 'root-like' fashion (Dubey et al. 2016). Observing nanotube formation in real time showed that these structures are formed in the course of minutes, displaying rapid movements.Nanotubes are composed of chains of membranous segments harboring a continuous lumen. Furthermore, a conserved calcineurin-like protein, YmdB (264 aas, O31775), is present in nanotubes and is required for both nanotube production and intercellular molecular trade.