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


1–40 μm

1–2 μm

0.8–2 μm


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


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 such as secretin, stalk protein, and needle filament; the flagellar apparatus has its own set of dedicated proteins that form the base, stalk, and tip.


Putative Functions of Nanotubes

Numerous studies have identified various possible roles for bacterial nanotubes, which researchers have observed under different growth conditions.


Species found

Culture conditions


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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