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Lecture 2-9 - Lecture 9 Diversity Bacteria Bacterial...

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Lecture 9 Diversity: Bacteria 3/7/2011 © Nicola Davies 2011 Diversity: Bacteria Lecture 9 March 7, 2011 2 Bacterial Diversity Bacteria divided into 23 phyla Denoted B1 through B23 Proteobacteria (B12) subdivided into 5 classes Contains 1300 species Chrysiogenetes (B5), Thermomicrobia (B7) and Dictyoglomi (B23) contain only one species Phyla divide bacteria into meaningful groups Share common characteristics Live similar lives 3 B4: Deinococcus-Thermus Gram-positive radiation-resistant cocci & rods Thick peptidoglycan layer (stain gram-positive) Inner and outer membranes Intermediate between gram+ and gram- Gram-negative thermophiles Thermus aquaticus yielded Taq polymerase 4 Deinococcus radiodurans Extremely resistant to gamma radiation, UV light, prolonged dessication Lethal radiation dose : Human: 500-1000 rads D. radiodurans survives over 5 million, grows at 6000 rads per hour Lethal double stranded DNA breaks: E. coli : survives 2-3 D. radiodurans : survives hundreds Rapid repair of DS DNA breaks likely underlies survival 5 Resistance in D. radiodurans Minor protection offered by carotenoid pigments and thick cell wall DNA repair underlies resistance Two mechanisms of DS DNA repair Single-strand annealing Reattaches DNA fragments with SS ends RecA-mediated homologous recombination
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