This simulation models how an unknown bacterium can be identified by various methods, such as observing the appearance of the organism, its stainability, determining the Guanine and Cytosine (G+C) base ratio content of its DNA, and sequencing its ribosomal RNA to compare it to known species. You will study bacteria found on a plaque scraping from a healthy human mouth.

One purpose of the classification of organisms is to describe the lines of evolutionary descent by creating a hierarchical family tree connecting the successive categories of species, genus, family, order, class, phylum, and kingdom. In most sexually reproducing plants and animals, this grouping is based on structural and physiological similarities, on evolutionary relationships, and the concept of species. A species is defined as a group of organisms that can interbreed and produce fertile offspring in mature members.

In bacteria, there are no sharp natural species boundaries because reproduction is asexual. Each individual reproduces by binary fission. The new individuals are genetically identical except for rare mutations. The transfer of genetic material between individuals involves only small pieces of DNA. This means that bacterial species have to be defined differently.

Researchers believe that the majority of bacteria have yet to be discovered. Scientists have identified about 5,000 species of bacteria from an estimated population of one million and more. It is estimated that the human mouth may harbor up to 500 species of unidentified bacteria.

Procedure:
1. Drag the pipette from the Gram stain container and drop the stain on the microscopic slide you wish to examine. Next, drag the stained microscopic slide onto the microscope's stage for viewing. Examine the organism's shapes and stainability on the monitor. Click on the Microbiology and Laboratory Handbook icon. Page forward or backward through the pages for clues to the organism's identity. Compare the shape and stainability of the organisms on the microscopic slide to the known species in the handbook.

2. Select the test tube containing ribosomal RNA for the unknown bacterium selected in Step 1. Drag the test tube containing ribosomal RNA to the ribosomal RNA Gene Sequencing Electrophoretic Unit. Results are displayed on the monitor. Determine the rate of similarity to data sets of ribosomal RNA sequences of known bacterial species (type strains) shown in the Microbiology and Laboratory Handbook.

3. Select the test tube containing DNA for the unknown bacterium selected in Step 1. Next, drag and drop the test tube containing DNA to the GC content measuring apparatus. Results are displayed on the monitor. Click on the Microbiology and Laboratory Handbook icon. Use the Guanine plus Cytosine (G+C) content of DNA determination method to compare the unknown DNA to a data bank of known DNA from bacterial species (type strains). Click the Close button to close the Microbiology and Laboratory Handbook overlay.

4. Click on the Table/Graph button. Record the data for each step into the Data Table. Use the Reset button to reset the simulation. Repeat Steps 1-4 and classify and identify the remaining unknown Bacteria species.

5. When all the data are analyzed and recorded in the Data table, answer the Journal Questions.