Green sulfur bacteria are often found at the greatest depths of all phototrophic cells in lakes, oceans, and microbial mats. This is because green sulfur bacteria
A) are very sensitive to UV irradiation, despite their reliance on light for energy.
B) are the only phototrophs that can use hydrogen sulfide as an electron donor for photosynthesis.
C) are strict anaerobes.
D) have chlorosomes that are very efficient at harvesting light, allowing them to perform photosynthesis where light intensities are very low.
Purple sulfur bacteria are
A) alphaproteobacteria that oxidize hydrogen sulfide in the presence of oxygen or nitrate.
B) gammaproteobacteria that use hydrogen sulfide as an electron donor for photosynthesis.
C) a phylogenetically heterogeneous group of microbes that reduce sulfate to sulfur.
D) thermophilic bacteria that reduce elemental sulfur to sulfide.
The Cyanobacteria are united by their ________, but their ________ is very diverse.
A) physiology / morphology
B) morphology / physiology
C) ecology / physiology
D) SSU rRNA sequences / physiology
The phylogenetic trees of the nifH and SSU rRNA genes are incongruent because
A) nitrogenase is an anaerobic enzyme.
B) nitrogenase evolves rapidly.
C) of horizontal gene transfer.
D) very few microbes have the nifH gene.
The vacuole of the giant sulfide-oxidizing bacterium Thiomargarita namibiensis contains ________ that is used to oxidize sulfide under ________ conditions.
A) nitrate / anoxic
B) sulfate / anoxic
C) oxygen / oxic
D) sulfur / anoxic
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