An Update on Mitochondria and Their Invaders

There is more to the bacterial invasion of mitochondria than we had known. Previously, we divulged that bacteria can be found within the mitochondria of certain Italian cockroaches, an unusual form of parasitism if there ever was one. Erin Banning of the Marine Biological Laboratory at Woods Hole told us of a paper that points out similarities between this invasion and that of Bdellovibrio. In both cases the predator grows in the periplasm of the host "cell"─an unusual place for a parasite to grow. The title of the paper tells all: "A symbiont of the tick Ixodes ricinus invades and consumes mitochondria in a mode similar to that of the parasitic bacterium Bdellovibrio bacteriovorus." We already wondered if the Bdellovibrio-type mechanism is limited to bacterial predation of bacteria. Sure, mitochondria were once bacteria, but... 

Thanks, Erin.

Comments

[Mark O. Martin]

It's an interesting speculation, and I look forward to seeing more research on this topic.

Many people have wondered/speculated about intracellular symbionts or parasites of bacteria and archaeans. There have been a couple of reports, once again in unusual organisms found in insects (what is it with weird microbes and insects---a derivative of Haldane's aphorism about God having an inordinate fondness for beetles?)

von Dohlen CD, Kohler S, Alsop ST, McManus WR. (2001). "Mealybug beta-proteobacterial endosymbionts contain gamma-proteobacterial symbionts." Nature 412:433-436.

and

Thao ML, Gullan PJ, Baumann P. (2002). "Secondary (gamma-Proteobacteria) endosymbionts infect the primary (beta-Proteobacteria) endosymbionts of mealybugs multiple times and coevolve with their hosts." Appl Environ Microbiol.68:3190-3197.

I have discussed this with several colleagues, and they are all more than a little suspicious of this idea, and suspect that prokaryotic (sorry, Norm) phagocytosis may be lethal to the cell. On the other hand, Liz Sockett's group at Nottingham took some dynamite EMs of Bdellovibrio invading E. coli, creating a bdelloplast with the predator's flagellum protruding outside the prey cell wall!

So who knows? What I do know is that the microbial world echoes Haldane's famous statement that the universe (read "microbial world") is not stranger than we imagine; it is stranger than we can imagine.

What a great time to be a microbiologist!

[Andrew Staroscik]

A bit of a tangent, but this paper (http://tinyurl.com/3bvhzq ) from Environmental Microbiology has been in my 'to read' pile for a while. In it, the authors speculate that a Bdellovibrio type invader might have given rise to the mitochondria itself.

Elio replies: I am grateful to you for pointing out this tantalizing speculation