Lewis/Life - Teaching Techniques

Chapter 22 - Teaching Techniques

A. General Tips
Because this is such a wide-open field, there are many innovative ideas you can try. First of all, recall your course objectives. What do your students need and why do they need it? Then decide on your approach.
Three areas of research that could easily be assigned for additional study or extra credit are pathogenic microbiology, industrial microbiology, and genetic engineering. Much information is available and students could easily do reports on assigned topics.
Students often have some real problems accepting that most bacteria are not harmful. They also have trouble believing that our bodies were designed to ward off pathogens. I have included more information on this in the notes for Chapter 39.
You might wish to copy and distribute to your students the Overview of Chapter Objectives flowchart found at the beginning of this Instructor's Manual Chapter.
B. Possible Approaches to the Chapter
I suggest you begin this chapter with a non-quiz. Some true or false questions might include: 1) Most bacteria are harmful. 2) In an ideal world, our environment (including our food) would be sterile. 3) Viruses and bacteria are the same thing. 4) We really don't use enough antibiotics to get rid of all the disease causing bacteria. Of course all four answers are false. You may be surprised at the misconceptions your students have.
I also suggest you make some bacterial plates. Acquire several nutrient agar plates. (Trypticase soy agar plates or blood agar plates will do if regular nutrient agar plates are unavailable.) The more general the nutrient the better. Bring these plates, some tape, and a wax pencil to class. Tell the students the plates are sterile. Open one plate at the beginning of lecture and let it remain open on your desk until the end of the class period. At that time close and label your plate. Also at the beginning of class ask for a few volunteers to put "something" on the other plates. Possibilities include: a kiss, a touch with the hand, a shake of the hair, money, a speck of dust off the floor, etc. The students should tape the plates shut and label them.
Keep the plates until the next class period. At that time, pass the plates around and let the students examine the growth. Rules of thumb: If it is raised and fuzzy, it is probably a fungal colony. If it is smooth and round, it is probably a bacterial colony. The fungus Aspergillus will be black; the gray and green fungal growth is probably a penicillium species. Yellow bacterial colonies are usually Staphylococcus aureus and if a colony looks like it spread all over the plate, it probably did. Swarming is a characteristic of certain motile bacteria.
Caution students not to open the plates. Another rule of microbiology: When working with bacteria, be safe and assume all bacteria are pathogenic.
C. Hints Related to Specific Chapter Topics
- I.A. Archaea will be a totally new concept to most of your students, even ones who had a fairly solid biology background in high school. You might point out that many of the organisms now classified as archaea have been known for many years; others are very recent discoveries. It is only in the last few years that the uniqueness of these creatures has begun to unravel.
  Some students will have learned that the cyanobacteria are the blue-green algae, and they will not like leaving this mind set. They just won't want to call some of their aquarium scum bacteria. Use this as an opportunity to show the difficulties of classification. By appearance and outward lifestyle, cyanobacteria certainly seem like classic algae. Internal observation, however, reveals the classic moneran characteristics.
- I.B. Obviously you could make an entire class (or an entire course) on microbial ecology. If you are adventuresome, you might use microbial ecology as the focal point for your entire moneran presentation. If you do not do this, your students should at least understand the complexity of the microbial world as well as the impact the microbes have on all aspects of our existence.
  Lewis refers to Figure 22.2 and spends some time discussing the role of bacteria in the digestive system of the ruminates. Note that the bacteria also provide a major source of protein for the animals. (Ruminates are herbivores.)
- II. How much information do you want your students to remember about moneran diversity? I suggest you make a chart of the key points you expect your students to know.
  Suggest that for extra credit the students research the giant bacterium, Epulopiscium fishelsoni.
- II.A. Agar is still technically called by its older name, agar-agar. Agar was discovered by Frau von Hesse, a friend of Robert Koch who was one of the greatest microbiologists ever. Frau von Hesse was visiting the South Seas when she noticed the natives thickening their soups and stews with an alga (seaweed). She thought of her friend Robert Koch who was having a difficult time finding substrates on which to grow bacteria.
  Agar has several unique properties. First, virtually no organism actually metabolizes agar; therefore it remains in tact, which is an improvement over other substrates such as potatoes. Second, agar is a solid at room temperature; this is a definite improvement over gelatin, which many organisms do digest and which is liquid at room temperature. Also, agar melts at the boiling point but can be cooled to about 50° C before it solidifies.
- II.B. One interesting organism not able to survive in laboratory culture is Treponema pallidum, the causitive agent of syphilis.
- III.A. Lewis states that round, rod, and spiral are the three most common moneran shapes. It is good to emphasize that these are just three of the shapes. Some books lead students to believe that these are the only shapes.
  In 1884 Hans Christian Gram, a Danish physician, discovered the staining technique named for him while he was trying to better observe the bacteria in the wounds and exudate of his patients.
  You might wish to note that there are gram-variable organisms.
- III.C. Stress Table 22.1. Add any additional terms you deem appropriate. For instance, in the second column of page 445 Lewis uses the terms photolithotrophic autotroph and chemoorganotrophic heterotroph.
  This question sometimes comes up: Are there facultative aerobes? Some (not all) microbiologists state that there are some, but we do not have to worry about them. That is probably where it should be with your class.
- IV. Stating that the typical bacterium is 2 µm is strictly generic. Be certain your students realize this.
- IV.A. The argument is sometimes made that all cells have some form of glycocalyx. If any of your students have heard that, accept it. Not all bacteria form endospores; many do not. Interestingly, many endospores form while conditions are good. It is almost as if the bacterial cell were storing things up for a harsh winter. If conditions are good, the endospores release, rejuvenate, and reform at regular intervals.
- IV.B. As you work through this section, I strongly suggest you either draw the diagrams or work closely with Figures 22.10 and 22.11.
- IV.C. The symptoms listed on page 450 for gonorrhea apply primarily to men. Gonorrhea in women is often vaginal or cervical, rather than urethral. It should be noted, however, that Neisseria gonorrhoeae can attack any mucous membrane in the body.
- V.A. Remind your students that classification of the archaea is still a matter of debate.
- V.A.2. Some of the halophiles are so delicate that in order to transfer them from one tube to another tube, the inoculating loop must first be dipped in salt.
  When people use salt as a preservative, water leaves the cells in question in order to "equalize" the salt. The dehydrated cell is no longer able to reproduce.
- V.A.3. Lewis mentions Yellowstone National Park. Ask your students if any of them have been there. If any have visited Mammouth Hot Springs or any of the geyser basins at Yellowstone, they will probably be more than willing to share their impressions.
- VI. Lewis very wisely explains what it means to "fix" nitrogen. So many students do not understand this term, and are afraid to ask.
  E. coli genetics is mentioned. Your students might be interested in knowing that we know more about the DNA of E. coli than we do about our own DNA.
  An interesting point someone in your class might like to research is the function of the "ice bacteria."
  The last paragraph of this section mentions chelation and the use of bacteria in bioremediation. Some of these bacteria are so efficient in cleaning up water in mining operations that the water is actually drinkable without further treatment as it comes out of the treatment facilities.