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Monday, January 24, 2011

A tale of two nucleobionts: Holospora obtusa and Holospora undulata

I got really intrigued about the paramecium endonuclear symbionts.  So this will be the subject of our first research challenge in class.  I got really intrigued because these bacteria  (Holospora)  don't just happen to end up in the macro or micronucleus, they possess specific mechanisms to discriminate and enter these nuclei and they also bind to chromatin.  They even dramatically change their morphology to perform this feat.  This is fascinating because I thought that perhaps viruses were the only creatures which possess designs to invade nuclei.  So what could these nucleobionts be doing?  According to a speculative theory developed by my colleague Todd Wood these creatures might be doing something very significant.  But you will have to find his paper to find out more about this (AGEing).  I cannot give away anymore hints now, but stayed tuned to this blog for more hints.


  1. Question: "So what could these nucleobionts be doing?"
    Holospora might provide genetic information that enhances a Paramecia’s ability to react against the effects of an unusual heat increase. "Paramecia bearing the macronuclear-specific symbiont Holospora obtusa survived better than symbiont-free paramecia, even under high temperatures unsuitable for growth.”

    “Even after the removal of the bacteria from the hosts by treatment with penicillin, the resulting aposymbiotic paramecia nevertheless maintained their heat shock-resistant nature for over 1 yr." The maintaining of the heat resistance, even after removal of the bacteria, could explain why the Holospora’s genetic information is the primary factor in the heat resistance of the Paramecia. Also, this suggests that this heat resistance information is transferred to the Paramecia’s nucleus, because the Holospora itself can be absent when a Paramecium exhibits the heat resistant trait.

  2. Here is the citation information for the quotes: Hori M, Fujii K, Fujishima M.

    Division of Environmental Science and Engineering, Graduate School of Environmental Science and Engineering, Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8512, Japan.

  3. As I mentioned in class, perhaps the bacterium have some sort of protein on their membrane that only interacts with a protein on the nuclear membrane. Thus, the bacterium can 'find' the correct destination through some sort of protein recognition system.

    I read that the H. obtusa can only reproduce in the macronucleus. Maybe a by-product of the reproduction of the H. obtusa is useful in the macronucleus of the Paramecium for one of the functions it controls.

    One abstract of a scientific paper on the topic said that these Holospora bacterium in the Paramecium have been found to increase heat and osmotic stress resistance. Maybe that's why it is favorable to the Paramecium for the bacterium to live there. Perhaps the bacterium lives in the Paramecium because that is the only place it can reproduce. There doesn't seem to be much detailed information on what the Holospora bacterium do except to 'infect' Paramecium.

    One really interesting thing I read was that a 'clean' Paramecium would be infected by the bacterium if the Paramecium was grown in the same medium as an infected Paramecium. How in the world would the bacterium (inside the macro- or micronucleus) first know that there was a 'clean' Paramecium in close proximity? Second, how would the bacterium then get out of the nuclear membrane? Third, how would the bacterium know which direction to go? It doesn't seem like protein recognition would explain that.

  4. Liz, for your second question, it seems that the bacterium exit the nuclear membrane when the cell undergoes mitosis. Before division, most of the bacteria can be found in a connecting strand. This connecting strand is deformed and finally expelled from the daughter cells, along with the bacterium.

  5. All good input, however you might want to keep some of the really good ideas private and only share with your research challenge group.

    Dr Francis