1.
The researchers who observed that magnetite was produced by bacterial cultures from the deep subsurface (see Box 25.1 on page 491) carried out a follow-up experiment. They treated some of the cultures with a drug that poisons the enzymes involved in electron transport chains. In cultures where the drug was present, no more magnetite was produced. Does this result support or undermine their hypothesis that the bacteria in the cultures perform anaerobic respiration with Fe3+ serving as the electron acceptor? Explain your reasoning.
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2.
Streptococcus mutans obtains energy by oxidizing sucrose. This bacterium is abundant in the mouths of Western European and North American children and is a prominent cause of cavities. The organism, and cavities, are virtually absent in children from East Africa. Propose a hypothesis to explain this observation. Outline the design of a study that would test your hypothesis.
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3.
Use of condoms slows the spread of sexually transmitted diseases like syphilis, gonorrhea, and AIDS. According to the transmission-rate hypothesis, should the virulence of these diseases be increasing or decreasing in countries where condoms have recently increased in popularity?
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4.
Suppose that you’ve been hired by a firm interested in using bacteria to clean up organic solvents found in toxic waste dumps. Your new employer is particularly interested in finding cells that are capable of breaking a molecule called benzene into less toxic compounds. Where would you go to look for bacteria that might be able to metabolize benzene as an energy or carbon source? How would you design an enrichment culture capable of isolating benzene-metabolizing species?
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5.
Would you predict that disease-causing bacteria, like those listed in Table 25.4, obtain energy from light, reduced organic molecules, or reduced inorganic molecules? When they perform respiration, which substance would you predict that they use as an electron acceptor? Explain your answer.
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6.
Why would it be advantageous for certain strains of Escherichia coli to secrete a toxin that causes diarrhea? (This bacerium is a common and usually harmless inhabitant of the human gut.)
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