The Mitochondria Eaters
From an aesthetic level, I find ticks themselves to be rather repulsive. But if you look inside this gruesome little insect–oh, how things get fascinatingly bizarre! In a way, a tick’s hidden secret is even more horrible than mere blood-sucking. I’m talking about a carnivorous microbe that devours a eukaryotic cell’s powerhouses: the mitochondria eater.
On the lookout for intracellular pathogens such as Rickettsia bacteria during the 1970s, David Lewis examined a species of ticks, Ixodes ricinus, found in England under electron microscopy. He certainly found some bacteria, but they were doing something really weird–they invaded only mitochondria and not other organelles of the cell.
Nowadays, there’s still not that much known about this mysterious bacterium–it still doesn’t even have a proper name. (Scientists are still calling it IricES1 for Ixodes ricinus endosymbiont.) What is known is that IricES1 belongs to a group of bacteria called alpha-proteobacteria and its niche is restricted to the eggs of the female tick. A bacterium will invade the mitochondria of the egg and eventually consume the entire mitochondrion matrix until there is nothing but “a swollen empty sac containing a rich population of bacteria.” Luckily for the tick, the egg itself seems unharmed and when fertilized, will develop into a seemingly healthy tick.
But with this predatory/symbiotic relationship restricted to the female germline, one can’t help but draw parallels between this and other sex related symbiotic relationships such as Wolbachia and its myriad invertebrate hosts. But can this be something totally different or is this just one stage in the process of a bacterium becoming inexorably linked to its host?