An international team of researchers has solved a long-standing microbial mystery; we now know how the bacterium Bdellovibrio bacteriovorus can invade another bacterium, then grow inside of it without destroying the host. The researchers are interested in harnessing the mechanisms of Bdellovibrio so that we can use it to kill antibiotic-resistant bacteria. The work has been reported in Nature Microbiology.
To learn more, the scientists first created substitutes for components of bacterial cell walls that were fluorescently labeled. They combined their creation, fluorescent D amino-acids (FDAAs) with super-resolution microscopy so they could see what was happening to the cell wall. They found that Bdellovibrio makes a small, reinforced porthole in the membrane of the host bacteria. After getting into the cell, Bdellovibrio then seals the hole shut from the inside.
“The bacteria being invaded are 100 million times shorter than a ship like the Queen Mary 2, and the invading bacteria are 500 million times narrower. The materials used for the welding aren’t metal of course but are natural D-amino-acids. These are mirror image forms of the ‘L’ amino-acids found in the proteins of foods and of our bodies,” explained Professor Liz Sockett, of the University of Nottingham.
“We discovered a second process where the invading bacteria effectively ‘plaster’ the inside of the bacterium they are invading, again using the D amino-acids. This makes the inside of the bacterium a more reinforced home for the Bdellovibrio to live inside. This is important as a previous paper showed that the invaded bacterial walls are initially rounded-up and weakened early in the invasion process.”
When Sockett visited Indiana, Erkin Kuru, who was a Ph.D. student then, suggested that fluorescent amino acids be added to two different bacteria when the Bdellovibrio was attacking. The FDAAs would allow the investigators to see what happens at every stage.
The team had a breakthrough watching the porthole being made. It has a central pore and is surrounded by a ring of amino acids that reinforce the hole. The FDAAs illuminated the event. Then the Bdellovibrio invader got into the cell and filled it with more material containing FDAAs. Thus, the host cell won’t burst; the predator can make a meal of the cell contents without everything leaking out.
The invading bacterium proceeds to move around the cell, adding more FDAAs to the interior cell wall, and not only at the porthole. The scientists likened the predator to a painter creating frescoes on a molecular scale. The purpose is to reinforce the host’s entire membrane, so it will not collapse until the predator has finished its meal.
“It is remarkable to see this in action at such a tiny scale and also useful. Knowing more about the mechanisms used by the invading predatory bacteria could help design new ways of killing pathogens. Now that the invasion processes have been defined it should be possible to gather all the tools needed to invade and consume pathogenic bacteria without releasing large amounts of their pathogenic cell materials by them bursting,” Sockett concluded.
The video above features previous work by Professor Sockett; Bdellovibrio attacks an E. coli bacterium.