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MCB 229 Spring 2000 Study Guide 18 Prof. Terry

1. The broadest meaning of "symbiosis" is "intimate living together" for at least part of a life cycle, but there is often confusion about what this implies. The following terms are used to distinguish a variety of types of symbiosis. What does each term imply? Ectosymbiosis, endosymbiosis, commensalism, mutualism, syntrophism. Note that one very important type of symbiosis, "parasitism", is not discussed in this chapter -- it is the subject of chapter 29.
2. For each of the following symbioses, identify special adaptations. Are these obligatory (i.e., the organisms require the symbiosis in order to survive) or facultative? Lichen symbiosis, termite-protozoan symbiosis, hydrogen fermenter-methanobacterium symbiosis, tube worm-reduced sulfur chemolithotrophic bacterial symbiosis, rumen symbiosis.
3. What are gnotobiotic animal? What is an axenic animal? Are humans gnotobiotic at any stage of life? How do germfree animals compare to normal animals? How are such animals produced? How are they maintained? What benefits do a normal microbiota provide, based on the study of germfree animals?
4. The term "microbial flora" has lost favor with the microbial community (after the 3 domains revelation, any lingering suspicions that bacteria are more "plant-like" than "animal-like" has evaporated.). The best term to describe microbial communities associated with animal tissues is microbiota.
5. For each of the following environments, what are major constraints that limit microbial growth? Skin, mouth, respiratory tract, stomach, small intestine, large intestine, urethra, vagina.
6. For each of the environments listed in the previous question, what is the dominant microbiota? Don't memorize this, but do spend some time examining Fig. 28.8 and associated text. Are any tissues devoid of microbiota in healthy individuals?
7. What microbe causes acne? Why is this disease usually limited to the adolescents, as opposed to children or older adults?
8. What microbiota is found on the conjuctiva of the eye?
9. How does the incidence of microbiota in the stomach compare with other regions of the GI tract?
10. How does the incidence of microbiota in the colon compare with other regions of the GI tract? What are the dominant types of colon microorganisms? How abundant is E. coli?
11. Overnight broth cultures typically produce as much as 10¹⁰ bacteria/ml. How does this compare with the concentration of bacteria in feces? (Apologies for dwelling on this delicate subject, but it's one statistic every microbiologist should know!) Fecal concentration = ________ microbes/gram.
12. About how many microorganisms are excreted daily by one adult human? ________ Considering that the mass of a single bacterial cell is approximately 10^-12 gram, how many grams of microorganisms a day are you contributing to the UConn sewage plant?
13. What microbiota is found in the upper reaches of the urinary tract? What are the major microbes present in the vagina? How do they affect pH?
14. What are probiotics? Is there such a thing as a "universal" probiotic for animals? Under what conditions should you consider giving probiotics to an animal (or to yourself)? What specific microbes are often used as probiotics? What foods could you take that would provide these microbes? (Hint: see pp. 920-921).