Numerous microbial associations and interactions drive and regulate nutrient fluxes in the ocean. Symbiotic interactions are the best example and are key drivers of ecological diversification and evolutionary innovation on Earth1. Besides symbiotic, other kinds of interactions exist between free-living bacteria; for example, the uptake of shared metabolites, horizontal gene transfer (HGT), quorum signaling, and exchange of substances via extracellular vesicles or pili2-5. Physical contact between cells of marine cyanobacteria had not been studied thus far. Here, we show a new mechanism of direct interaction between the marine cyanobacteria Prochlorococcus and Synechococcus, the intercellular membrane nanotubes (NTs).
We present evidence of inter- and intra-genus exchange of cytoplasmic material between neighboring and distant cells of cyanobacteria mediated by NTs. We visualized and measured these structures in axenic and in natural samples. We show that NTs are produced between living cells, suggesting this is a relevant communication system in vivo. The discovery of nanotubes acting as exchange bridges in the most abundant photosynthetic organisms in the ocean may have significant implications for the survival marine microbial interactions. The transfer of compounds between these small bacteria in areas with poor nutrient concentrations might be an important factor in their ecological success in the ocean ecosystems. Furthermore, nanotubes-mediated cell interaction provides additional evidence for the importance of cooperation between these marine cyanobacteria, showing they act as a collective rather than individual cells in the context of marine ecosystems.