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.
Type 3 Secretion Systems, e.g., Injectisomes and Flagella
Multiprotein complex; tubular
30–130 nm; commonly 40–70 nm
6–11 nm; lumen diameter ~3 nm
8–10 nm; lumen diameter ~2.5 nm
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.
Transfer of materials (RNA, proteins, amino acids, toxins)
Bacillus megaterium, B. subtilis, Clostridium acetobutylicum*, Desulfovibrio vulgaris*, E. coli,
Solid or liquid media, depending on the study
Adhesion to mammalian cells
Enteropathogenic E. coli
Cell, 177:683–96.e18, 2019
Adhesion to nanopillars and the formation of biofilms
Soft Matter, 16:7613–23, 2020
Stress response in dying cells placed under pressure
Nat Comm, 11:4963, 2020
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