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Mark O. Martin

Ah, the rough wooing of macrosymbiont and microsymbiont. And who can say which entity is "running the show"?

It's like those "Chinese box" souvenirs: boxes inside boxes inside boxes. Or Russian nesting dolls.

This is a post I will be discussing in class on Wednesday, Elio and Merry. Much kudos and tips of metaphorical hats.

Two things:

1. We all suffer from from what I tell the students to call "colicentricity"---what we easily observe in one system is assumed to be the rule throughout nature. We microbiologists know better. So the large scale transfer of DNA may be MUCH more common (and perhaps ongoing) than we suppose:

Gladyshev, EA, Meselson M, and IR Arkhipova. (2008). "Massive horizontal gene transfer in bdelloid rotifers." Science 320: 1210 - 1213.

Who knew that rotifers could be "sponges" for diverse genetic information (and how wonderful that Matt Meselson was part of this--what a career!)? It could be called something like "omnisexuality" (and I will avoid the obvious puns). More seriously, I have wondered about other organisms that undergo cryptobiosis, like tardigrades: do they do this kind of thing as well?

2. Regarding Wolbachia---what is with the bacteriophages?

Bordenstein SR, et al. (2006). "The tripartite associations between bacteriophage, Wolbachia, and arthropods." PLoS Pathol. 2(5): e43.

Does this mean that phages infest the cytoplasm of insect cells inhabited by Wolbachia, and even move from cell to cell and insect to insect in search of new Wolbachia, or is there some niche outside the insect where the bacterium grows and is susceptible to phage attack? We know that the association is old, yet the phages seem intact (I would expect them to be sandblasted down to pseudogenes by the dead hand of Darwin if they were not currently infectious to their host).

This takes me back to my old friend Caedibacter and its symbiosis with Paramecium (and the remarkable "killer" trait). This too may be due to the co-opting of a lysogenic phage!

Jeblick J and J Kusch. (2005). "Sequence, transcription activity, and evolutionary origin of the R-body coding plasmid pKAP298 from the intracellular parasitic bacterium Caedibacter taeniospiralis." J. Mol. Evol. 60: 164 - 173.

So we have to think of ourselves as not simply a series of ecological niches for our microbiota to inhabit and with which to interact. It seems as if our cells themselves contain a series of microenvironments in which prokaryotes can grow...and their own DNA elements (phages, transposable elements) are all jockeying for position at the same time.

It's a wonderful if dizzying time to think about microbiology.

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