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Difficulty: HardMust Be True / Most Strongly Supported

Microbiologists investigating deep-sea hydrothermal ecosystems at the Gorda Ridge established the following rules regarding bacterial metabolism:

• Any chemolithoautotrophic bacterium from the Gorda Ridge that fixes carbon via the Calvin-Benson-Bassham (CBB) cycle cannot utilize sulfur oxidation for ATP synthesis unless it expresses the enzyme Rubisco I.
• Every chemolithoautotrophic bacterium from the Gorda Ridge that expresses Rubisco I exhibits obligate anaerobic respiration.
• No bacterium from the Gorda Ridge that exhibits obligate anaerobic respiration synthesizes polyphosphate granules for intracellular storage.

A newly classified specimen, Strain GR-9, is a chemolithoautotrophic bacterium from the Gorda Ridge that is known to synthesize polyphosphate granules and fix carbon via the CBB cycle.

Statement: Strain GR-9 does not utilize sulfur oxidation for ATP synthesis.

Answer: Answer

Answer

True. A rigorous chain of contrapositive deductions proves that Strain GR-9 cannot utilize sulfur oxidation for ATP synthesis.
The claim must be true because the factual premises force a valid deductive contrapositive chain: Polyphosphate synthesis implies non-obligate anaerobiosis, which implies absence of Rubisco I, which in turn prohibits sulfur oxidation for any organism using the CBB cycle.

Step-by-Step Solution

1
Deduce Strain GR-9's respiratory classification from its storage mechanism
Strain GR-9 does not exhibit obligate anaerobic respiration.
Premise 3 states that obligate anaerobes do not synthesize polyphosphate granules. The contrapositive dictates that any bacterium synthesizing polyphosphate granules is not an obligate anaerobe.
2
Deduce whether Strain GR-9 expresses Rubisco I
Strain GR-9 does not express Rubisco I.
Premise 2 establishes that expressing Rubisco I necessitates obligate anaerobic respiration. By contrapositive, since Strain GR-9 does not exhibit obligate anaerobic respiration, it cannot express Rubisco I.
3
Apply the conditional constraint on carbon fixation and energy pathways
Strain GR-9 does not utilize sulfur oxidation for ATP synthesis.
Premise 1 establishes that for CBB-fixing chemolithoautotrophs, utilizing sulfur oxidation requires Rubisco I. Because Strain GR-9 fixes carbon via CBB but lacks Rubisco I, it cannot utilize sulfur oxidation.

Key Concept

Multi-Premise Conditional Chaining and Contrapositive Inference
Estimated Time:2m 0s
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Must Be True / Most Strongly Supported

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