OR Rather… SIX IN A?
In some cases, the symbionts have moved their genes to the hosts’ genomes so that the genes are missing from Tremblaya could be found in the DNA of the cochineal. In fact, the team discovered that the cochineal genome contained at least 22 genes of bacterial origin. But surprisingly, none of these genes came from Tremblayanor of Moranella !
They actually came from three separate lines of bacteria. All three of these groups contain members that regularly colonize insect cells, but none are found in cochineal today. Perhaps they colonized the insect’s ancestors, donated their genes to them, and then died out. “These genes are like ghosts from former symbionts,” explained Molly Hunter of the University of Arizona. There are many examples of bacteria donating their genes to animals, but “this degree is impressive, especially since it comes from so many different sources,” she added.
These borrowed genes do not remain inactive. They also participate in the production of amino acids, thus closing gaps in the production chain that are neither Tremblaya none of them Moranella not able to fill. The citrus scale is actually a mix of six different species, three of which are not even present anymore!
WHAT NAMES SHOULD YOU GIVE THEM?
Life history is full of bacteria that have become permanent residents in other cells. Our own cells, as well as those from all animals, plants, and fungi, contain small structures called mitochondria, which were once free-living bacteria. Today they are organelles: spaces in larger cells that perform specialized tasks. For example, mitochondria are batteries that give us energy.
So the bacteria Tremblaya is she a symbiote, or has she already become an organelle? “The distinction is a matter of debate and definition,” said Martin Kaltenpoth of the Max-Planck Institute for Chemical Ecology. Tremblaya lives permanently inside other cells, helps its host survive and has lost many genes. Each of these elements places it in the category of organelles.
But there are also two major differences. As free-living bacteria grew into mitochondria, they shrank by transmitting many of their genes to their hosts. Tremblaya did not: she became small because she supported herself Moranella. Organelles also tend to be permanent and irreplaceable: If all of your mitochondria suddenly disappeared, you would die very quickly. But Tremblaya can be replaced. In some mice, another bacterium has infected it. “I would not call it an organelle,” McCutcheon says.
Instead of arguing about the names we could give them, it is more important for him to define the details of this partnership, and many mysteries still need to be solved. For example, how Moranella it shares exactly its enzymes with Tremblaya ? After all, Moranella does not make any of the transport proteins that normally export molecules. In 2011, the team suggested it Moranella could simply burst and release its contents to Tremblaya. “It was speculation. We just could not think of another solution,” McCutcheon said.
But maybe they were right. The cell wall off Moranella, the layer that holds its interior together consists of peptidoglycans, molecules that the bacterium cannot make alone. Instead, it relies on cochineal genes, including those borrowed from other bacterial groups! By disabling these genes, the cochineal could destabilize Moranellablast it and drop its contents against Tremblaya. Perhaps she controls the relationship between her current symbiotes using genes borrowed from his old symbionts.
Would not ruin it Tremblaya also ? No, because the bacterium has lost so many essential genes that it cannot make its own cell wall or membrane. According to McCutcheon, she gets these barriers thanks to cochineal. If true, that would be great, because it would mean it Tremblaya is dependent on cochineal to define its own limits. Without its host, it would just be a bunch of molecules floating in a liquid.
“It’s still speculation, but we can at least experiment now,” McCutcheon says. He could, for example. turn off the peptidoglycan-forming genes of the cochineal and see what happens to the number of Moranella.
According to his observations, John McCutcheon’s peers were already very impressed. “John is known for his unique contributions to understanding the evolution of intracellular mutualisms in insects, and this is another excellent piece of work by his group,” Kaltenpoth said. “I found this article a masterpiece,” Hunter added.