Natures wonders: bacteria can spear amoebas (Introduction)

by David Turell @, Thursday, August 17, 2017, 23:51 (966 days ago) @ David Turell
edited by David Turell, Friday, August 18, 2017, 00:15

Bacteria can defeat amoebas who try to engulf them:

"Bacteria have to watch out for amoeba. Hungry amoebae hunt them: they catch them with their pseudopodia and then absorb and digest them.

"However, some bacteria know how to defend themselves. One of these is Amoebophilus, which was discovered by researchers at the University of Vienna a few years ago. This bacterium cannot only survive inside amoebae, but also thrive: the amoeba has become its favourite habitat.

"The shooting mechanism consists of a sheath attached to the bacterium's inner membrane by a baseplate and an anchoring platform. João Medeiros, a doctoral student in Professor Martin Pilhofer's group at ETH, explains the mechanism: "The sheath is spring-loaded and the micro-dagger lies inside it. When the sheath contracts, the dagger is shot outwards extremely quickly through the bacterial membrane."

"Bacteria absorbed by the amoeba end up in a special digestive compartment surrounded by a membrane. "Our results suggest that the bacteria are able to shoot the dagger into the membrane of the amoeba's digestive compartment," says Désirée Böck, also a doctoral student in Pilhofer's group and lead author of the study published in the journal Science. This results in disintegration of the compartment, which is an inhospitable environment for the bacteria, and release of the bacteria. Once outside the digestive compartment but still inside the amoeba, the bacteria can survive and even multiply.

"The process by which the digestive compartment is destroyed is not yet known. "It may be that rupture of the membrane is due solely to mechanical reasons," says Pilhofer. However, it is conceivable that the daggers of the Amoebophilus bacteria are impregnated with a kind of arrow poison - with membrane-degrading enzymes. The blueprints for such enzymes are contained in the bacteria's genome, as Matthias Horn, professor at the University of Vienna, and his colleagues were able to show.


"Systems related to the micro-daggers are also found elsewhere in biology: viruses that specialise in the infection of bacteria (bacteriophages) use such systems to inject their genome into microorganisms. Some bacteria can even release similar micro-devices into their surroundings to fight off competing microorganisms.

"The scientists present for the first time the complete spatial structure of a shooting mechanism inside a cell in its natural context. They also show for the first time details of the baseplate and membrane anchor


"Micro-daggers had previously been found only as individual devices. In Amoebophilus, however, the scientists from Zurich and Vienna have now found apparatuses that occur in clusters of up to 30. "You could call them multi-barrel guns," says Pilhofer.

"The researchers also used genomic comparisons to investigate how Amoebophilus evolved its daggers. "The relevant genes are very similar to those of the bacteriophage injection systems," says Pilhofer. "We assume that the genes from ancestors of today's bacteriophages established themselves in the bacteria's genome a long time ago."

"Genomic comparisons suggest that the micro-daggers occur not only in Amoebophilus, but also in numerous other bacterial species from at least nine of the most important bacterial groups."

Comment: This seems to be a complex molecular machine structure, which may be so complex it can only be developed by design. It seems that these bacteria are brighter than H. habilis who couldn't invent a spear!

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