Microbial Diversity MIC/PLP329 Final Exam Fall 2001

Microbial Diversity MIC/PLP329 Final Exam Fall 2002 Answer three of the six following questions (about one page per question; open book, no discussion among students). In addition to the class handouts and syllabus links, do some web/medline searching on your own. Answers are due on Thursday December 13 by 5pm.

1. Discuss mechanisms of spore resistance in Bacillus subtilis (see syllabus and links to Dr. Nicholson’s lecture).

2. Discuss the variety of roles that fungi play in our daily lives. Include the importance of both pathogens and saprobes. (Dr. Orbach’s links from syllabus web page)

3. Discuss mechanisms by which species of Cryptospiridium invade and are pathogenic to animal host cells. Why might host animals die? (Dr. Riggs)

4. Explain why RNA viruses are often denoted "quasipecies". How does this concept relate to the emergence of antiviral drug resistance in HIV? (See Dr. Collins handout papers)

5. Provide several lines of evidence that argue for co-evolution between whitefly- transmitted viruses and their vector, Bemisia tabaci, which have led to strict virus-vector specificity. (If you chose this question, send Dr. Brown an email and she will send you the required references)

6. The Microviridae have evolved to be small. In the last few years a subfamily of the Microviridae, whose members infect obligate intracellular bacteria like Chlamydia, has been defined. The members of this subfamily, the Chp-like viruses, are significantly smaller than the ΦX174-like subfamily. ΦMH2K is a member of this subfamily. One of the major differences between the two subfamilies is the absence of genes in the Chp-like viruses that encode the external scaffolding and five-fold related spike proteins (see figure). The Chp-like viruses also have coat proteins which form large protrusions at the three-fold axes of symmetry (see figure). In addition, the internal scaffolding protein may have evolved into a structural protein. Some functions of the ΦX174 internal and external scaffolding proteins are summarized below.

Functions of the ΦX174 external scaffolding protein. A. Stabilizes three-fold axes of symmetry in the procapsid. B. Stabilizes the two-fold axes of symmetry in the procapsid. C. Placement of the five-fold related spike protein.

Functions of the ΦX174 internal scaffolding protein. A. Prevents premature association and aggregation of coat protein. B. Stabilizes the two-fold axis of symmetry in the procapsid.

A. Based on the information given in this question, hypothesize why the Chp-like viruses have loss their external scaffolding proteins and why their internal scaffolding proteins have evolved into structural proteins. (see Reading 2 of Dr. Fane’s lecture: Liu et al. Virol. 2000 Apr;74(8):3464-9).

B. The authors hypothesize that Vp3 is equivalent to the ΦX174 internal scaffolding protein. Of the data they present, which are the most convincing and why?