Infographic: What Are Bacterial Nanotubes?

While questions remain about how common bacterial nanotubes are and what they do, researchers have identified key differences in their structure and function that set them apart from pili used for mating, injectisomes that transfer virulence proteins, and flagella that power swimming in many microbes.

	Bacterial Nanotubes	Conjugative Pili	Type 3 Secretion Systems, e.g., Injectisomes and Flagella

Composition; structure	Lipids; segmented	Proteins; helical	Multiprotein complex; tubular
Length	1–40 μm	1–2 μm	0.8–2 μm
Width	30–130 nm; commonly 40–70 nm	6–11 nm; lumen diameter ~3 nm	8–10 nm; lumen diameter ~2.5 nm
Materials transferred	Antibiotic resistance factors, metabolites, toxins	Plasmids	Injectisomes for the transfer of virulence proteins; flagella for motility
Proteins involved in formation	CORE complex (same proteins as the flagellar base) and hydrolases that help make a hole in the cell wall	“Transfer” (Tra) class of proteins such as pilin, TraL, and TraF	The injectisome complex has various proteins...

Putative Functions of Nanotubes Numerous studies have identified various possible roles for bacterial nanotubes, which researchers have observed under different growth conditions.
Function	Species found	Culture conditions	Citations
Transfer of materials (RNA, proteins, amino acids, toxins)	Bacillus megaterium, B. subtilis, Clostridium acetobutylicum, Desulfovibrio vulgaris*, E. coli, enteropathogenic E. coli, Staphylococcus* aureus	Solid or liquid media, depending on the study	Cell, 144:590–600, 2011; Nat Comm, 11:4963, 2020; Nat Comm, 6:6283, 2015; Cell, 177:683–96.e18, 2019
Adhesion to mammalian cells	Enteropathogenic E. coli	Liquid media	Cell, 177:683–96.e18, 2019
Adhesion to nanopillars and the formation of biofilms	Pseudomonas aeruginosa	Liquid media	Soft Matter, 16:7613–23, 2020
Stress response in dying cells placed under pressure	B. subtilis	Liquid media	Nat Comm, 11:4963, 2020

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Infographic: What Are Bacterial Nanotubes?

Unlike other cellular appendages, bacterial nanotubes are made solely of lipids and can connect the cytoplasm of different microbial species.

Putative Functions of Nanotubes

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