"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

February 16, 2010

February 16 - Holospora undulata

So, according to the news, one of the big trends in fashion this year is that prints are back – especially paisley. And one cannot think of paisley (if one is a biologist, anyway), without picturing Paramecium. But, of course, paramecium is not a parasite – they are free-living unicellular organisms that zip around with their cilia and gobble up bacteria. But they have parasites, including the alphaproteobacterium, Holospora undulata. Paramecium have two kinds of nuclei – there is one macronucleus, which contains the genes for all the proteins involved in being a Paramecium on a day-to-day basis, and one or more micronuclei, which contain the genes involved in reproduction and essentially represent its “germ line.” Holospora undulata bacteria live in the micronuclei of their hosts. (A different species, Holospora obtusa, lives in the macronucleus.) These bacteria exist in two different forms – short rods, which are the reproductive forms, busily dividing in the nucleus, and a longer infectious form, which leave the host cell and enter the environment. Paramecia become infected when they ingest H. undulata along with the other bacteria that they’re munching up. The Holospora escape from the phagosome and move to the nuclear membrane where they bind to receptors and then enter inside. Because these bacteria infect one of biology’s favorite lab organisms, not surprisingly some very nice research on infectious disease and the ecology of hosts and parasites have been done using this system as a model.

Photo from the Encyclopedia of Life.

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