A virus can infect dead organisms

Between animate and inanimate: bacterium turns into virus

A working group led by Christoph M. Deeg from the University of British Columbia has discovered a parasitic bacterium that is apparently on its way to the half-animate intermediate world of viruses. While searching for viruses that attack single-celled plankton, the working group came across the peculiar organism Chromulinavorax destructans, which attacks bacteria-eating protozoa. As the team reports in a publication on the preprint server »BioRxiv«, the parasitic microbe does not have its own metabolism, but only uses the resources of the infected microorganism - even the energy molecule ATP cannot produce it itself. Outside of its host, the bacterium appears to be as dead as a virus: it cannot convert nutrients or divide.

The parasite only comes to life when it is eaten by its host. He hijacks the food vacuole, quasi the stomach of the larger host, and converts it for his own purposes. As Deeg and his team write, the bacterium then attracts its mitochondria, so that soon two thirds of the host cell are filled with these cell power plants that supply the parasite with energy. Then large bubbles form in the cell, which apparently contain genetic material for the offspring of the bacterium; these bubbles divide into new, mature parasite cells, the host organism bursts, and the attackers swarm out again.

The life cycle of C. destructans corresponds in almost every detail to that of classic viruses; The size of the cells is also similar to the giant viruses that the working group was actually looking for. Do two things C. destructans Nevertheless, to a bacterium: On the one hand its origin - its genome shows that the microbe belongs to a group of parasitic bacteria. On the other hand, before it leaves the pathogen, it carries out a cell division step, for which it also has its own genes. The rest of its genetic makeup consists mainly of genes for transport molecules that pull nutrients from the host cell. Possibly will Chromulinavorax destructans in the future further reduce its genome and become a real virus. Only his genetic makeup will then reveal his unusual career.