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In a study of deep-sea hydrothermal vents in the Mariana Trench, marine biologist Dr. Elena Rostova and her team analyzed the metabolic pathways of the newly discovered chemolithoautotrophic bacterium *Sulfurimonas maris*. The researchers found that unlike related species from shallower vents that rely exclusively on hydrogen oxidation, *Sulfurimonas maris* possesses genes encoding both hydrogenases and enzymes for the oxidation of thiosulfate. However, laboratory assays showed that the bacterium only expresses the thiosulfate oxidation genes when local concentrations of dissolved oxygen drop below a specific threshold of 5 micromoles per liter5\text{ micromoles per liter}. This genetic adaptation allows *Sulfurimonas maris* to maintain energy production in highly fluctuating oxygen zones near the vent chimney.

Based on the text, what is true of the expression of thiosulfate oxidation genes in *Sulfurimonas maris*?

  1. A
    It is dependent on the presence of hydrogenases to facilitate the chemical process.
  2. It is restricted to environments where the concentration of dissolved oxygen is less than 5 micromoles per liter5\text{ micromoles per liter}.Answer
  3. C
    It is observed in all related chemolithoautotrophic bacteria residing in shallower vents.
  4. D
    It occurs continuously to prevent energy depletion when the bacterium moves away from the vent chimney.

Answer

The correct answer is that the expression of thiosulfate oxidation genes in the bacterium is restricted to environments where the concentration of dissolved oxygen is less than 5 micromoles per liter5\text{ micromoles per liter}.
The text states that laboratory assays showed *Sulfurimonas maris* only expresses the thiosulfate oxidation genes when local concentrations of dissolved oxygen drop below a specific threshold of 5 micromoles per liter5\text{ micromoles per liter}. This directly supports the fact that the expression is restricted to environments with dissolved oxygen levels below this threshold.

Step-by-Step Solution

1
Analyze the text for details regarding the expression of thiosulfate oxidation genes in *Sulfurimonas maris*.
The text states that laboratory assays showed the bacterium only expresses these genes when local concentrations of dissolved oxygen drop below a specific threshold of 5 micromoles per liter5\text{ micromoles per liter}.
To identify the specific condition under which the genes are expressed.
2
Evaluate the answer choices against this explicit detail.
The choice stating that expression is restricted to environments with dissolved oxygen levels below 5 micromoles per liter5\text{ micromoles per liter} directly matches the text, while other choices make unsupported assumptions or contradict the text.
To select the option that is directly supported by the text without speculation.

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