Cap, sheath and base: a cross-section of the injection system of a bacterium. | Graphic: J. Xu et al. (2022)

It sounds like science fiction. Some bacteria use tiny mechanisms to shoot ‘arrows’ out into their environment. They are presumably used to communicate with other bacteria, and could also have biomedical applications. Until recently, only four such systems were known, but an ETH team led by Martin Pilhofer has now identified further, novel injection mechanisms in the genes of bacteria, and has determined their structure. They include the marine bacterium Algoriphagus machipongonensis. The illustrations here show cross-sections some 30 nanometres across of the cap, sheath and base of the injection system (respectively, from left to right), revealing how different proteins form its sixfold, symmetrical structure.

J. Xu et al.: Identification and structure of an extracellular contractile injection system from the marine bacterium Algoriphagus machipongonensis. Nature Microbiology (2022)