Dichotomous key test

As you have learned, biochemical test results can be used to identify unknown species of microorganisms. You have analyzed results from several biochemical tests now, and so you should be aware that biochemical tests are performed to determine which enzymes/metabolic pathways are present and active in a particular species. When this is done using an unidentified (unknown) organism, you can compare test results to many known species to determine the identity of the unknown species. You will be doing this in the Bacterial Unknowns assignment soon.

First, to prepare for the process of identifying an unknown species, you must construct a dichotomous key that you will later use.

STEP 1: Read This Introduction to Dichotomous Keys
Dichotomous means “dividing into two parts.” As discussed in lecture, a dichotomous key is a flow chart that is constructed to organize information that is useful to distinguish between different species. It consists of a series of characteristics of which there are two varieties, so that different species can be divided based on differences in these characteristics.

When constructing a dichotomous key that may be used to identify bacteria, we start by dividing a group of bacteria into two groups based on a certain characteristic, such as the Gram-stain reaction. Then, each of the two subgroups is subdivided into two groups based on a second characteristic, and so on. For example, a dichotomous key used to identify unknowns from a group of four Gram-negative cocci bacteria might look like the following:

example dichotomous key.jpg

As you can see, in order to construct a dichotomous key, you need several test results from known species.

STEP 2: Examine the Data
Carefully review the “Summary Biochemical Test Results” data for the twelve species in the Excel file below. In this file are biochemical test results from twelve different bacterial species. These are the data that you will use to build your dichotomous keys.