Squashing_staining nodules - Koch's postulates Various...

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1 Koch’s postulates Various Experimental Techniques to Determine Bacterial Identity To verify the identity of the bacteria contained within root nodules, the nodules must be surface sterilized and then squashed on a selective medium (see later section). Many of the bacteria we investigate are tagged with a gene that enables antibiotic resistance such the gene for neomycin resistance or tetracycline resistance. Some of the bacteria will be labeled with reporter genes including gusA or lacZ . Others, especially many of the “unknowns”, will grow only on a particular growth medium. Squashing out the nodules will allow you to fulfill Koch’s postulates , i.e. determine that the bacteria isolated from the nodules are what was used as an inoculum, and thereby capable of eliciting nodule development on the appropriate host roots. Robert Koch (1843-1910; Nobel Prize in Medicine, 1905) What are Koch’s postulates? Robert Koch was a German microbiologist who demonstrated that cattle with anthrax developed the disease because they were infected by Bacillus anthraces . Up to that time, people were unclear on the connection between disease and an infectious agent. Koch proved this by isolating the bacteria from the blood of diseased animals, and then after injecting a healthy animal with some of the blood, he found that the healthy animal developed the same disease as the first animal and then later died.
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