Tunneling nanotubes (TNT) between free living amoebae: a new route for microbial resistance and pathogenesis?

Free-living amoebae (FLA) have multiple roles in the ecology of microorganisms. Tunneling nanotubes (TNTs) are cytoplasmic bridges now considered as a major pathway of cell-to-cell communication for eukaryotic mammalian cells. Interestingly, TNTs can be hijacked by microorganisms to promote their intercellular spreading. Here, type 1 and type 2 of TNTs were observed between trophozoites of Acanthamoeba castellanii . Both types of TNTs contained actin while tubulin was only detected in TNT1. Hovering freely above substratum, TNT1 connected isolated long distance motile amoebae with a length up to 82 µm. In contrast, TNT2 (< 5µm) bridged short distance between FLA trophozoites. The mechanism of TNT formation in amoebae is likely to be through cell dislodgement. To our knowledge, this is the first time that TNTs were observed between unicellular eukaryotes. It suggest a primitive mode of cell connectivity and upset current knowledge. This opens many study opportunities including microbial exchange and resistance.