mcb 229
Extra Credit Options
Last revised: Monday, April 21, 2003


  • Purpose
    The purpose of these short essays is for you to learn more about certain aspects of microbiology, and for you to communicate what you have learned succintly and clearly. Your target audience should be the intelligent layman, not a microbiologist. Explain any unfamiliar terms. Avoid unnecessary jargon. Don't quote the text or other source; rewrite it so that you explain clearly. Be selective in what you include.

  • Length
    Essays should be roughly 1200 words in length (about 3-4 pages long).

  • References
    You must cite at least one reference (which may include your text). Use APA conventions for reference citation. If you reference sources by computer, see "How do I document sources from the World Wide Web in my works-cited list?", from the MLA. If you need electronic assistance with writing, visit the Purdue Writing Lab.

  • Submission
    Papers must be printed, double-spaced, and handed in to the instructor (or Prof. Terry's mailbox in BSP 1st floor MCB office) no later than the due date to be eligible for extra credit.

  • Grading
    Each paper submitted on time may earn: Points will be added to the final course grade. Any evidence of plagiarism will result in zero points for all students involved and denial of any extra credit points otherwise earned.

    Topic 1: "Microbes and extreme enviroments"
    Deadline Thurs. March 6, 2003

    It is becoming clear that certain bacteria and archaea can survive ("grow" may be too strong a word) under conditions that used to be thought of as impossible: the high pressures found at the ocean bottom, inside rocks at depths as great as 1 mile, in boiling hot springs. Find one or a few examples of such microbes that interest you and discuss what we know and what we don't know about them.

    Here are a few web links you might explore to help choose a topic.
    Topic 2: Applications of Microbial Genetics
    Deadline Tues. April 1, 2003

  • Some Sample topics The following are only a few possible suggestions. I list them because they might otherwise escape your notice.

    Horizontal Gene Transfer
    We know that horizontal gene transfer can occur. What are the mechanisms? How frequent are such events? Can transfers occur across species? Across genera? Across domains? What is the impact of such transfers on evolution? There are dozens of questions that come to mind when approaching this type of process, almost any of which could be a good subject for a short paper.

    Is 16S RNA the best "yardstick" for studying evolution?
    Initial enthusiasm for the use of 16S (small subunit) RNA as a highly reliable indicator for evolutionary separation turned to skepticism by some when it was shown that phylogenetic trees constructed using different genes placed some organims into very different locations. Should we be using other genes instead? Are the results of 16S RNA phylogeny still considered valid? For a good recent overview of this situation see, "Phylogeny of Bacteria beyond the 16S rRNA Standard", by Wolfgang Ludwig and Karl-Heinz Schleifer. ASM News, Nov. 1999. (Alternate "secure" access here)

    What is a bacterial "Species"?
    In eukaryotes, the term "species" has a biological meaning: members of the same species can reproduce. If they can't, they belong to different species. Bacteria lack mechanisms for sexual reproduction, so the term "species" must be defined differently. For instance, the definition of a bacterial species is based on a DNA/DNA reassociation threshold. Organisms with greater than 70% relatedness based on such analysis are considered to belong to the same species. By this yardstick, humans, chimpanzees, and lemurs would all belong to the same species. Does "species" have any real meaning at the bacterial level, or should we seek alternatives? For a good discussion of this problem, with some interesting alternatives, see "Bacterial Biodiversity: a Time for Place ", by James T. Staley. ASM News, Oct. 1999. (Alternate "secure" access here)

    Why do some plasmids contain clusters of antibiotic resistance genes?
    The evolution of antibiotic resistance genes makes perfect sense from an evolutionary perspective. As people use more antibiotics, only those bacteria carrying resistance genes can survive. However, many examples exist of plasmids that carry resistance genes for multiple antibiotics, not just one. How did this arise? Can we explain this situation strictly in terms of a Darwinian "survival of the fittest" model? For a good discussion of this issue, see Clustering of Antibiotic Resistance Genes: Beyond the Selfish Operon Jeffrey G. Lawrence. ASM News, May 2000. (Alternate "secure" access here)

    Agrobacterium and genetic engineering
    Bacteria of the genus Agrobacterium have the novel ability to invade plant tissues and induce tumors. This has been best studied in Agrobacterium tumefaciens, which carries tumor-inducing genes in its "Ti plasmid". This plasmid is proving to be one of the most useful tools available to move a variety of genes into plants. Over 35 agricultural crop plants have been engineered using the Ti plasmid. For a good introduction, see "Mercenary Microbes" at the web page of the International Society for Microbial Ecology, and associated links, for some introduction to this organism and its uses.
    Topic 3: "Emerging Diseases"
    Deadline Tues. May 6, 2003

    At least one "new" disease seems to have appeared every year during the past few decades: Lyme Disease, AIDS, Legionnaire's Disease, Hantavirus, West Nile Virus in the U.S., SARS, and many others. What is an "emerging disease"? Where do they come from? Are they really "new" or have they been around but suddenly been discovered?

    These are a few of the many interesting questions that surround "emerging diseases". If you want to write a short paper on this topic, I'd like you to focus on two issues:
    1. Write a short introduction to the broad question of "emerging diseases", in which you answer some of the questions raised above based on whatever scientific evidence we possess.
    2. Choose one example of a newly emerging disease and briefly discuss what we know of this disease. What are its virulence factors? Where did it come from? Why has it "emerged"?

    For reference material, you should spend some time searching in the scientific literature. Most of the published work in this area will not be available on the web outside of scientific journals, although you may find the the "Emerging Diseases" web page at Beloit College helpful for some online resources. I've downloaded a few PDF files to our website that you may find helpful as a starting point:
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