Microbiology

 
                                                Nuclear waste eating bacteria

                                                   Deinococcus radiodurans

Extremophilic bacterium, most radition-resistant organism known.

It can survive in acid, dehydration, vacuum and cold condition: polyextremophile

It has been listed as the world's toughest bacterium in the Guinness book of world records.

D. radiodurans is large, spherical bacterium. Four cells stick together, forming a tetrad.

Colonies are smooth, convex, and pink to red in color. The cells stain is Gram-Positive.

D. radiodurans does not form endospore and is nonmotile. It is an obligate aerobic chemoorganoheterotroph. It uses oxygen to make energy from organic compounds in its environment. It is often found in habitats rich in organic materials, such as soil, feces, meat, or sewage, but has also been isolated from dried foods, room dust, medical instruments and textiles.

It is extremely resistant to ionizing radiation, desiccation, oxidizing and electrophilic agents.

Deinococcus make its resistance to radiation by having multiple copies of its genome and rapid DNA repair mechanisms. It usually repairs breaks in its chromosomes within 12–24 hours through a 2-step process. First, D. radiodurans reconnects some chromosome fragments through a process called single-stranded annealing. In the second step, multiple proteins mend double-strand breaks through homologous recombination. This process does not introduce any more mutations than a normal round of replication would.

Scanning electron microscopy analysis has shown that DNA in D. radiodurans is organized into tightly packed toroids, which may facilitate DNA repair.

D. radiodurans is capable of genetic transformation, a process by which DNA derived from one cell can be taken up by another cell and integrated into the recipient genome by homologous recombination. When DNA damages (e.g. pyrimidine dimers) are introduced into donor DNA by UV irradiation, the recipient cells efficiently repair the damages in the transforming DNA as they do in cellular DNA when the cells themselves are irradiated.