For decades, researchers studying deep-sea hydrothermal vent ecosystems assumed that primary productivity relied exclusively on chemosynthetic bacteria utilizing hydrogen sulfide. However, a 2018 expedition to the Mid-Atlantic Ridge led by Dr. Elena Vance revealed an unanticipated metabolic pathway. Vance and her team isolated a novel strain of gammaproteobacteria, designated strain Alpha-7, that derives energy primarily from the oxidation of dissolved iron rather than sulfur compounds.
Unlike sulfur-oxidizing microbes, which deposit elemental sulfur externally as a metabolic byproduct, strain Alpha-7 precipitates insoluble iron oxides internally within specialized intracellular vesicles. Laboratory assays demonstrated that this internal sequestration protects the bacterium from iron toxicity while simultaneously generating a localized proton gradient across the inner membrane. This gradient drives ATP synthesis even in low-oxygen microenvironments surrounding fluid discharge vents. Furthermore, Vance observed that while sulfur-oxidizing strains thrive predominantly in high-temperature zones exceeding 60°C, strain Alpha-7 achieves peak metabolic rates in cooler, ambient waters between 15°C and 25°C. This temperature preference enables Alpha-7 to colonize peripheral regions of vent fields previously deemed biological deserts.
Based on the passage, which of the following is explicitly stated regarding the metabolic byproducts of strain Alpha-7?
- AThey consist of elemental sulfur deposited on the outer cell membrane.
- They are insoluble iron oxides stored inside specialized intracellular vesicles.Answer
- CThey are accumulated externally to neutralize hydrogen sulfide toxicity.
- DThey are released into high-temperature vent fluids exceeding 60°C.
- EThey consist of ATP molecules excreted directly into ambient waters.