Conan the Bacterium

Radiation Resistance and Deinococcus radiodurans

Jacqueline Parker

Outline

What is Deinococcus radiodurans? History and Phylogeny Repair Mechanisms of Deinococcus Current Interest in Deinococcus Conclusion and References

What is Deinococcus radiodurans?

“Little berry that withstands radiation”

Resistant to dehydration and genotoxic chemicals, Deinococcus has the ability to withstand remarkably large amounts of ionizing radiation.

Deinococcus thrives at levels of 1.5 million rads and can withstand levels of up to 3.0 million

History and Phylogeny

First appeared in the 1950s in canned meat that had been experimentally irradiated as means of preservative

Represented on many phylogenetic trees to be close in evolutionary distance to another widely known extremophile Thermus aquaticus

Phylogenetic Tree

Phylogenetic Tree

Repair Mechanisms of Deinococcus

Radiation results in double stranded breaks in the DNA

Repair Mechanisms of Deinococcus

Deinococcus is able to withstand and repair radiation damage sometimes resulting in 200 or more double-stranded breaks in the DNA at one time

2 Main Steps:

1: single-strand annealing

2: RecA and homologous recombination

RecA and homologous recombination

Theories

Deinococcus has 4-10 DNA molecules per cell. When grown under conditions which cause a reduction in genome copy number, Deinococcus becomes less resistant to radiation.

“Life-Saver Hypothesis” Circular DNA is easily stacked with identical DNA sequences near each other.

Current Interest in Deinococcus

Bioremediation: Deinococcus as a vehicle for metabolizing residual chemical wastes

Deinococcus radiodurans equipped with genes enabling the organism to metabolize metals such as Uranium would be a lucrative and safer way to eliminate waste

Ability to withstand drought and high doses of radiation may have been indicative of other origins

Conclusion

Deinococcus has the ability to withstand remarkably large amounts of ionizing radiation using repair mechanisms that include single-strand annealing and the protein RecA and homologous recombination

Different theories are being investigated as to how these repair mechanisms are utilized to promote efficiency in the organism

Deinococcus is currently being researched as a viable tool for industrial clean up uses that may include doses of radiation that would otherwise be lethal to other organisms

ReferencesBrown, James et al. “Universal trees based on large combined protein sequence

data sets” Nature 28 (2001) 281-285.

Gupta, Radhey S. “Protein Phylogenies and Signature Sequences: A Reappraisal of Evolutionary Relationships among Archaebacteria, Eubacteria, and

Eukaryotes” Microbiology and Molecular Biology Reviews 62 (1998): 1435-1491.

Makarova, Kira S. et al. “Genome of the Extremely Radiation-Resistant Bacterium Deinococcus radiodurans Viewed from the Perspective of

Comparative Genomics” Microbiology and Molecular Biology Reviews 65 (2001): 44- 79.

Rothschild, Lynn H. Insight Nature 409 (2001) 1092-1101.

Venkateswaran, Amudhan et.al. “Physiologic Determinants of Radiation Resistance in Deinococcus radiodurans” Applied and Environmental Microbiology 66 (2000) 2620-2626.

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