Bacteria are the oldest forms of life on earth. Their first record dates around 3.5 billion years ago and are unicellular organisms that constitute the basic entities in the evolution of other organisms. They are very dynamic units that when finding appropriated conditions will rapidly replicate to generate new bacteria, they have also the capacity to receive genetic information, through Horizontal Gene Transference, that may confer them new functions. The long time they have inhabited the earth in addition to their high replication rates and their capacity to horizontally exchange genetic material have allowed them to colonize almost every environment on earth, from highly cold, to highly hot (hot springs, Fig 1), but also salties and acidic ones.
Bacteria genomes are typically formed by a single chromosome that is not surrounded by any membrane, it is freely arranged in the cell cytosol, such as in the well studied E. coli. However, it has been seen unusual genome arrangement in extremophiles bacteria. Deinococcus radiodurans can be considered as a polyextremophilic bacterium, because it can resist, not only radiation, as its name suggest but it is also halophylic, thermophylic, acid and desiccation resistant. Interestingly D. radiodurans has two chromosomes, a big and a small one. This bacterium after dividing initially does not completely separates but it stays connected in a tetrahedral arrangement. Depending on the genome and its arrangement bacteria can play adaptive functions. Kikuchi et al. (1999) showed and extensive inter chromosomal recombination in this organisms to form a multimeric chromosome, this would occur even in the absence of radiation, this high recombination capacity may serve as a system for radio resistance of this bacterium (Fig 2).
This resistance to radiation could bring an alternative way for storing the humanity information in case of a nuclear catastrophe. In fact, in 2003 U.S. scientists translated the Disney song of “It´s a Small World” into several 150bp DNA unities and inserted them into this bacterium. After 100 generation they were able to recover the initial codified song completely unchanged (http://www.newscientist.com/article/dn3243#.VRgvG0ZjUz4).
It is not clear how is the evolution mechanism among species resistant to ionizing radiation but there are two hypotheses. The first is that this mechanism is provided by a vestigial system of DNA repair from ancestral prokaryotic organisms and that it has been preserved for the advantages they bring. Second, is that this phenotype has arisen in unrelated species through horizontal gene transference (Cox & Battista, 2005). I may be in favor of this last hypothesis, since the events of ionizing radiation are low in the modern earth. But in the other hand, we can hypothesize that since these particular extreme environments motivate several strong selective pressures, then genome modifications, such as genome rearrangements, could promote or decrease the competitiveness of each organism for the few available niches.
References
Cox, M. M., & Battista, J. R. (2005). Deinococcus radiodurans—the consummate survivor. Nature Reviews Microbiology, 3(11), 882-892.
Kikuchi, M., Narumi, I., Kitayama, S., Watanabe, H., & Yamamoto, K. (1999). Genomic organization of the radioresistant bacterium Deinococcus radiodurans: physical map and evidence for multiple replicons. FEMS microbiology letters, 174(1), 151-157.
McDowell, Natasha (2003) Data stored in multiplying bacteria. Extracted the 27 March 2015. In : http://www.newscientist.com/article/dn3243#.VRgvG0ZjUz4
Bacteria genomes are typically formed by a single chromosome that is not surrounded by any membrane, it is freely arranged in the cell cytosol, such as in the well studied E. coli. However, it has been seen unusual genome arrangement in extremophiles bacteria. Deinococcus radiodurans can be considered as a polyextremophilic bacterium, because it can resist, not only radiation, as its name suggest but it is also halophylic, thermophylic, acid and desiccation resistant. Interestingly D. radiodurans has two chromosomes, a big and a small one. This bacterium after dividing initially does not completely separates but it stays connected in a tetrahedral arrangement. Depending on the genome and its arrangement bacteria can play adaptive functions. Kikuchi et al. (1999) showed and extensive inter chromosomal recombination in this organisms to form a multimeric chromosome, this would occur even in the absence of radiation, this high recombination capacity may serve as a system for radio resistance of this bacterium (Fig 2).
This resistance to radiation could bring an alternative way for storing the humanity information in case of a nuclear catastrophe. In fact, in 2003 U.S. scientists translated the Disney song of “It´s a Small World” into several 150bp DNA unities and inserted them into this bacterium. After 100 generation they were able to recover the initial codified song completely unchanged (http://www.newscientist.com/article/dn3243#.VRgvG0ZjUz4).
It is not clear how is the evolution mechanism among species resistant to ionizing radiation but there are two hypotheses. The first is that this mechanism is provided by a vestigial system of DNA repair from ancestral prokaryotic organisms and that it has been preserved for the advantages they bring. Second, is that this phenotype has arisen in unrelated species through horizontal gene transference (Cox & Battista, 2005). I may be in favor of this last hypothesis, since the events of ionizing radiation are low in the modern earth. But in the other hand, we can hypothesize that since these particular extreme environments motivate several strong selective pressures, then genome modifications, such as genome rearrangements, could promote or decrease the competitiveness of each organism for the few available niches.
References
Cox, M. M., & Battista, J. R. (2005). Deinococcus radiodurans—the consummate survivor. Nature Reviews Microbiology, 3(11), 882-892.
Kikuchi, M., Narumi, I., Kitayama, S., Watanabe, H., & Yamamoto, K. (1999). Genomic organization of the radioresistant bacterium Deinococcus radiodurans: physical map and evidence for multiple replicons. FEMS microbiology letters, 174(1), 151-157.
McDowell, Natasha (2003) Data stored in multiplying bacteria. Extracted the 27 March 2015. In : http://www.newscientist.com/article/dn3243#.VRgvG0ZjUz4