The type 6 secretion system is a bacterial weapon that resembles a crossbow with an arrow. At the end of the arrow sits a pointy spike which carries the toxin into the neighbouring bacterium. The spikes of these arrows are made of three of the same proteins and bacteria can have multiple of these spikes carrying different toxins. However, we do not really have a clue about how the spike carries the toxin into other bacteria.
In this paper published in Frontiers, we were looking very closely at this spike and how exactly toxin are glued to it.
We focused on two lipase toxins which are PldA and PldB in our favourite bacterium Pseudomonas aeruginosa. PldA and PldB are structurally very similar which means their killing actions are very similar. However, they seem to be delivered by different spikes.
When looking at the chromosome, we saw that the gene for PldA is right next to a gene for the spike VgrG4b and the gene for PldB is right next to a gene for the spike protein VgrG5. A random connection?
How we figured out the delivery mechanisms for PldA and PldB with their cognate spikes, you can find in the paper
or in my blog post