Type VI Secretion Systems just got cooler
Vibrio cholerae cells recycle the molecular "spear guns" fired by related species.
As microbiologists, when we are threatened by uninterested and bored students, there are a few "go-to" stories we can use to convince them that microbiology is actually pretty cool.
Arguably, one of the most attention grabbing examples are the Type VI secretion systems, the bacterial missiles/spears/harpoons (or whatever analogy you want to draw).
So we tell the students that bacteria literally swim around harpooning one-another with nano-spears and feel safe in the knowledge that that we have regained their attention, at least for a while.
Now, a new study from the University of Basel has shown that not only do bacteria throw spears around, but if an errantly thrown spear happens to hit a bacterial ally, the ally can simply reuse it. The researchers used mutants deficient in the Type VI secretion system (T6SS) in order to monitor what happened to the "spears" that were thrown around in a bacterial community.
Andrea Vettiger, author of the study, explains:
“The special thing about Vibrio cholerae is that it assembles spear guns all the time and fires them aimlessly. If one of T6SS-defecient bacteria is randomly hit, it disassembles the spear gun to its individual components, the shaft and tip proteins, and reassembles its own functional harpoon. Also the translocated tip-linked toxins can be recycled by the attacked cell. And even bacteria that no longer produce any proteins can assemble a T6SS by reusing the harpooned proteins provided by their neighboring sister cells.”
Take that bored students! Microbiology just got cooler.
T6SS deficient strains recycle and reassemble T6SS components
Bacterial type VI secretion system (T6SS) is a nano-machine that works similarly to a speargun. Rapidcontraction of a sling (sheath) drives a long shaft(Hcp) with a sharp tip and associated effectorsthrough the target cell membrane. We show thatthe amount and composition of the tip regulates initi-ation of full-length sheath assembly and low amountof available Hcp decreases sheath length. Impor-tantly, we show that both tip and Hcp are exchangedby T6SS among by-standing cells within minutes ofinitial cell-cell contact. The translocated proteinsare reused for new T6SS assemblies suggestingthat tip and Hcp reach the cytosol of target cells.The efficiency of protein translocation depends onprecise aiming of T6SS at the target cells. This inter-bacterial protein complementation can support T6SS activity in sister cells with blocked protein synthesisand also allows cooperation between strains to in-crease their potential to kill competition.
Andrea Vettiger, Marek Basler (2016). Type VI Secretion System Substrates Are Transferred and Reused among Sister Cells. Cell. DOI: http://dx.doi.org/10.1016/j.cell.2016.08.023