Q&A Hero

Q: Dissimilatory iron-oxidation is a relatively new metabolism and is restricted to one unusual phylum of bacteria.

Q: The ecological diversity of microbes is largely dependent on their complex morphological and structural diversity.

Q: Iron-reducing bacteria are obligately aerobic organisms that reduce ferric iron and oxidize hydrogen or organic compounds.

Q: Dissimilatory nitrate reduction results in the production of gaseous products, while assimilatory nitrate reduction results in the production of ammonia for biosynthesis.

Q: Denitrifying bacteria are often facultative anaerobes, capable of performing other forms of respiration or fermentation as well as nitrate reduction.

Q: Nitrogenase is an oxygen-sensitive enzyme even though many diazotrophs are aerobic microorganisms.

Q: There are currently no known predatory bacteria that are adapted to invade or kill nearby cells.

Q: Diazotrophs are obligately symbiotic bacteria that fix N2 into ammonia, thus providing a critical source of nitrogen to their host.

Q: Diazotrophs are found in all three domains of life.

Q: Unicellular cyanobacteria are the most abundant phototrophs in the ocean and perform 80% of marine photosynthesis.

Q: Akinetes and hormogonia are specialized cells, found in some cyanobacteria, that facilitate nitrogen fixation.

Q: Although Cyanobacteria contribute more than 35% of all photosynthesis on Earth, they are not visible in the natural environment.

Q: Prosthecae are an adaptation forA) anaerobic growth.B) cell differentiation under harsh conditions.C) nitrogen fixation.D) low nutrient aquatic environments.

Q: Bioluminescent microorganisms are found in which of the following groups? A) Firmicutes B) Thaumarchaeota C) Gammaproteobacteria D) Verrucomicrobia

Q: Bioluminescence is controlled by the gene regulatory mechanism called quorum sensing, wherein the A) depletion of oxygen is detected by an inducer molecule which activates transcription of the lux operon. B) accumulation of an inducer molecule activates transcription of the lux operon. C) absence of light activates an inducer molecule which activates transcription of the lux operon. D) host tissues produce an autoinducer molecule which activates transcription of the lux operon.

Q: Bioluminescence is catalyzed by luciferase, which creates light by A) shunting electrons from FMNH2 to O2, which releases energy in the form of light. B) reversing photosynthesis. C) hydrolyzing ATP. D) reducing LuxR.

Q: Bioluminescence develops when A) population density is high. B) oxygen is depleted. C) ambient light is low. D) the host induces the bioluminescence genes.

Q: Myxobacteria display ________ behavior and form ________ that produce myxospores. A) gliding / slime trails B) chemotactic / colonies C) phototactic / slime trails D) swarming / fruiting bodies

Q: Bdellovibrio species are ________ cells that replicate in the ________. A) symbiotic / gills of clams B) lithotrophic / deep subsurface C) predatory / periplasmic space D) denitrifying / sediments of freshwater lakes

Q: Acetogens are anaerobic organisms that produce acetate as the main product of their metabolism. They are important in A) the production of vinegar. B) the carbohydrate metabolism of the human gut. C) hydrothermal vent communities. D) the production of vitamin C.

Q: Which of the following functional groups form symbiotic relationships with Eukaryotes in deep sea environments? A) dissimilatory iron-oxidizers B) methanotrophs C) sulfide-oxidizers D) methanotrophs and sulfide-oxidizers

Q: Most methanotrophs are obligate ________ because ________. A) aerobes / the initial step of methane oxidation requires O2 B) anaerobes / methane is produced in anaerobic environments C) fermenters / methane only provides enough energy for fermentation D) heterotrophs / methane does not provide enough carbon for growth

Q: What is the difference between a methylotroph and methanotroph? A) Methylotrophs are strict anaerobes, while methanotrophs are strict aerobes. B) Methylotrophs use organic carbon lacking C-C bonds as electron donors and carbon sources, while methanotrophs exclusively use methane as an electron donor and carbon source. C) Methylotrophs produce organic carbon lacking C-C bonds, while methanotrophs exclusively produce methane. D) Methylotrophs are in Proteobacteria, while methanotrophs are in Archaea.

Q: Carboxydotrophic bacteria oxidize carbon monoxide to A) carbon dioxide. B) methane. C) acetate. D) glucose.

Q: A few bacteria are capable of growing on gases as the sole source of energy, carbon, and nitrogen. Which of the following combination of gases would support the growth of a bacterium in mineral media with NO other additions? A) H2, N2, CO2 B) H2, O2, N2, CO2 C) H2, H2S, N2, CO2 D) H2, O2, N2O, CO2

Q: Which of the following functional groups would you expect to find in aerobic iron- and sulfur-rich acidic mine drainage? A) dissimilative iron-oxidizers B) dissimilative iron-reducers C) purple sulfur bacteria D) purple sulfur bacteria and dissimilative iron-reducers

Q: In which of the following environments would you expect to find a high number of iron-reducing bacteria? A) acidic mine drainage B) deep subsurface C) open ocean D) agriculture soil

Q: Dissimilative iron-reducing bacteria couple the A) reduction of ferric iron or manganese to the oxidation of sulfur. B) reduction of ferric iron or manganese to the fermentation of sugars. C) oxidation of H2 or organic compounds to the reduction of ferric iron or manganese. D) reduction of ferric iron to photosynthesis.

Q: Which of the following traits do ammonia and nitrite oxidizers share? A) chemoorganotrophic B) autotrophic C) aerobic D) autotrophic and aerobic

Q: Escherichia coli is a chemoorganotrophic, facultative aerobe and belongs to the Proteobacteria phylum. Based on this information, which of the following functional groups does E. coli most likely belong to? A) green sulfur bacteria B) ammonia-oxidizing bacteria C) denitrifying bacteria D) nitrite-oxidizing bacteria

Q: What growth conditions would you use to enrich for ammonia-oxidizing bacteria? A) aerobic mineral media with ammonia and bicarbonate incubated in the dark B) anaerobic mineral media with acetate and ammonia incubated in the dark C) aerobic mineral media with acetate and ammonia, incubated in the dark D) anaerobic mineral media with ammonia and nitrate incubated in the dark

Q: Diazotrophs maximize nitrogenase activity by A) closely coupling N2 fixation with high rates of photosynthesis. B) fixing N2 at times when oxygen is absent or in low concentrations. C) producing specialized structures to protect nitrogenase from oxygen. D) producing specialized structures or fixing N2 at times when oxygen is absent to protect nitrogenase from oxygen.

Q: Nitrogenase is a critical enzyme in the nitrogen cycle because it catalyzes the A) assimilation of ammonia. B) dissimilative reduction of nitrate to nitrogen gas. C) fixation of nitrogen gas into ammonia. D) oxidation of nitrogen gas into nitrate.

Q: The Bacteria and Archaea are the ONLY domains in which organisms exist that can A) catalyze the transformation of inorganic nitrogen species for biosynthesis. B) assimilate nitrite. C) conserve energy from the transformation of inorganic nitrogen species. D) catalyze the incorporation of inorganic nitrogen species into biomolecules.

Q: In symbiotic associations between sulfur chemolithotrophs and eukaryotes such as tube worms and giant clams, the bacterial symbiont provides ________ while the host provides ________. A) nitrogen / carbon and oxygen B) sulfide / oxygen C) a carbon and energy source / stable sulfide and oxygen levels D) organic acids / stable sulfate levels

Q: Thioploca species contain large vacuoles that store ________, which is used to ________ under anaerobic conditions. A) nitrate / oxidize sulfide B) oxygen / oxidize sulfur C) sulfur / reduce nitrate D) glycogen / provide energy

Q: Dissimilatory sulfide-oxidizers use a variety of unique ecological strategies in order to A) avoid the toxicity of hydrogen sulfide. B) position themselves at interfaces where sulfide and oxygen meet. C) position themselves where there is sufficient light for sulfide oxidation. D) find organic carbon substrates.

Q: 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.

Q: 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.

Q: 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

Q: 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.

Q: Nitrogen fixation is A) rare among microorganisms. B) widespread among microorganisms. C) limited to Proteobacteria. D) common in Bacteria, but absent in Archaea.

Q: 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

Q: Which of the following pairs of microorganisms are NOT likely to form close associations or consortia? A) purple sulfur bacteria and dissimilative sulfur-reducers B) dissimilative sulfur-reducers and dissimilative sulfur-oxidizers C) nitrogen-fixing cyanobacteria and fungi D) nitrogen-fixing cyanobacteria and dissimilative sulfate-reducers

Q: Typical electron donors used by dissimilative sulfate-reducers are A) hydrogen, water, and hyrdrogen sulfide. B) hydrogen, lactate, and pyruvate. C) carbon dioxide, hydrogen, and water. D) sulfate, sulfur, and thiosulfate.

Q: Sulfate-reducing bacteria are a ________ that are found in ________ environments. A) monophyletic group / anoxic B) polyphyletic group / oxic C) morphologically distinct group / anoxic D) morphologically distinct group / oxic

Q: You are looking at a sample from the top green layer of a colorful bacterial mat. Using phase contrast and fluorescence microscopy, you see evenly spaced cells in the middle of a filament that are slightly smaller than the others. The smaller cells are not fluorescent, indicating they lack photosystem II, but the rest of the filament is fluorescent. What is the most likely function of the smaller cells in the filament? A) survival in the dark B) nitrogen fixation C) sulfur storage D) nitrate storage

Q: You are looking at a sample from the top green layer of a colorful bacterial mat. Using phase contrast and fluorescence microscopy, you see evenly spaced cells in the middle of a filament that are slightly smaller than the others. The smaller cells are not fluorescent, indicating they lack photosystem II, but the rest of the filament is fluorescent. What type of filamentous bacteria are you most likely looking at? A) purple nonsulfur bacteria B) green sulfur bacteria C) Acidobacteria D) Cyanobacteria

Q: The ecological diversity of phototrophic bacteria is illustrated by the different ________ that allow them to perform photosynthesis in low light environments such as deep in the ocean, in various sediments, and in thick layered mats. A) nitrogen fixation strategies B) bacteriochlorophyll and photosystems C) specialized stalked cells D) endospores and resistant cell types

Q: Which group of bacteria would you expect to find in a shallow clear hot spring with high concentrations of geochemically produced hydrogen sulfide? A) purple sulfur bacteria. B) single-celled Cyanobacteria. C) dissimulative sulfate-reducing bacteria. D) symbiotic diazotrophs.

Q: Aside from using light as a source of energy, another important part of the functional diversity of some bacterial phototrophs is their ability to A) bioluminesce. B) form prosthecate and stalked cells. C) fix nitrogen gas. D) degrade neurotoxins.

Q: Anoxygenic phototrophs A) may use a variety of electron donors for photosynthesis. B) are an ancient monophyletic group of bacteria. C) can be either autotrophic or heterotrophic. D) can be either autotrophic or heterotrophic and may use a variety of electron donors for photosynthesis.

Q: Which of the following conditions would you use to enrich purple nonsulfur bacteria from lake sediments? A) anoxic media with a good light source B) mineral media with ammonia and oxygen in the dark C) anoxic mineral media with an organic acid and a good light source D) mineral media with nitrate and acetate in the dark

Q: All microbial phototrophs A) fix carbon dioxide. B) use water as an electron donor for photosynthesis. C) fix carbon dioxide and use water as an electron donor for photosynthesis. D) use light energy to drive electron transport to generate energy.

Q: The only group of oxygenic phototrophic bacteria are the A) green nonsulfur bacteria. B) Chloroflexi. C) Cyanobacteria. D) Chlorobi.

Q: What form of photosynthesis evolved first on Earth? A) oxygenic B) anoxygenic C) autotrophic D) heterotrophic

Q: Functional traits can be shared between organisms with divergent SSU rRNA sequences because A) functional traits may be lost by different lineages over time. B) functional traits may evolve independently in different lineages over time. C) horizontal gene transfer can result in the transfer of genes between divergent lineages. D) functional traits may evolve independently, be shared through horizontal gene transfer, or be lost in divergent lineages.

Q: Microbial diversity is thought of in terms of phylogenetic diversity and functional diversity because A) similar functional traits are often found in divergent phylogenetic groups. B) phylogenetic diversity dictates functional diversity in microbes. C) functional diversity only pertains to functions that are not phylogenetic. D) similar phylogenetic groups almost always have similar functional traits.

Q: The aerated upper layer of soil is likely to have ________ concentrations of H2 for aerobic H2-oxidizing Bacteria, so these bacteria likely ________. A) high / thrive in such conditions by not competing with chemoorganotrophs B) high / generate important reducing equivalents as byproducts for other microorganisms in the soil C) low / do not occur in such habitats D) low / will need a chemoorganotrophic way to grow as well

Q: Alternative autotrophic routes to the Calvin cycle such as the reverse citric acid cycle and the hydroxypropionate pathway are unified in their requirement for A) CO2. B) coenzyme A. C) NAD(P)H. D) organic compound(s) formed.

Q: Ferrous iron (Fe2+) oxidation generally occurs in environments with A) alkaline conditions. B) high H+ concentrations. C) high oxygen content. D) little or no light present.

Q: Identifying carboxysomes in a bacterium suggests it A) contains the reverse citric acid cycle. B) has a deficient Calvin cycle and accumulated CO2. C) is in a carboxylic acid rich environment and is storing excess quantities for potentially harsh conditions. D) will use the Calvin cycle convert the concentrated CO2 into biomass.

Q: In most cases, the final product of sulfur oxidation is A) hydrogen sulfide. B) elemental sulfur. C) sulfate. D) thiosulfate.

Q: Regarding CO2 fixation mechanisms in the autotrophic green sulfur bacteria, A) Chlorobium uses the reverse citric acid cycle, and Chloroflexus uses the hydroxypropionate pathway. B) Chlorobium uses the hydroxypropionate pathway, and Chloroflexus uses the reverse citric acid cycle. C) both Chlorobium and Chloroflexus use the reverse citric acid cycle. D) both Chlorobium and Chloroflexus use the hydroxypropionate pathway.

Q: The Calvin cycle A) is responsible for the fixation of CO2 into cell material. B) utilizes both NAD(P)H and ATP. C) requires both ribulose bisphosphate carboxylase and phosphoribulokinase. D) uses CO2, NAD(P)H, and ATP to make biomass with ribulose bisphosphate carboxylase and phosphoribulokinase.

Q: Plastocyanin is a A) membrane-bound sac found in certain bacteria. B) photosynthetic pigment found in some bacteria. C) copper-containing protein in photosystem II that donates electrons to photosystem I. D) blue-green bacterium known for its unusual photoreactive complex.

Q: The path of electron flow in oxygenic phototrophs is referred to as the ________ scheme. A) E B) S C) Q D) Z

Q: The process by which electrons from the quinone pool are forced against the thermodynamic gradient to reduce NAD+ to NADH is called reverse A) proton motive force. B) reduction. C) electron transport. D) energy flow.

Q: Which group of microorganisms would the Calvin cycle LEAST likely be found in? A) anoxygenic Bacteria B) chemolithotrophic Bacteria C) cyanobacteria D) hydrocarbon catabolizing Bacteria

Q: What will happen to a cyanobacterium that has its photosystem II (PSII) blocked? A) Additional electron acceptors, such as NADP+, will be required to oxidize oxygen and overcome the lost PSII process. B) Anoxygenic photosynthesis only using photosystem I (PSI) could occur by using cyclic photophosphorylation and an alternative electron donor such as H2S. C) It will die from being unable to obtain energy for photosynthesis. D) Photons will generate excessive reactive oxygen species and the cyanobacterium will die as a consequence.

Q: "Special pair" is the name given to the ________ in the photochemical complex of the purple bacteria. A) two bacteriochlorophyll a molecules B) two bacteriochlorophyll b molecules C) two quinones D) two reaction centers

Q: Intracytoplasmic membrane systems housing vesicles known as chromatophores, which function in photosynthesis, are commonly found in A) algae. B) green sulfur bacteria. C) most autotrophic organisms. D) purple phototrophic bacteria.

Q: Two separate photosystems involved in electron flow is a hallmark of A) anoxygenic phototrophs. B) green sulfur bacteria. C) oxygenic phototrophs. D) purple bacteria.

Q: Light energy passes from phycobiliproteins to reaction centers in A) cyanobacteria. B) green sulfur bacteria. C) purple bacteria. D) most photosynthetic bacteria.

Q: At some of the lowest light concentrations, ________ can still grow well due to their ________, which effectively harvest photons for energy. A) green bacteria / antenna pigments B) green bacteria / chlorosomes C) purple bacteria / antenna pigments D) purple bacteria / chlorosomes

Q: Proteomic analysis of a microbial community indicated an abundance of phycobiliproteins. Which phototrophic group is likely active and abundant in this community? A) cyanobacteria B) eukaryotic phototrophs C) green bacteria D) prochlorophytes

Q: In contrast to chlorophylls, carotenoids function A) as accessory pigments that enable absorption of energy from higher wavelengths. B) primarily as photoprotection (but they also transfer some absorbed energy into reaction centers). C) to convert reactive oxygen species into usable energy. D) to quench toxic oxygen species.

Q: Bacteriochlorophyll and chlorophyll contain ________ as a cofactor. A) iron (II) B) iron (III) C) magnesium D) manganese

Q: In photosynthesis, NADH and NADPH are produced from NAD+ and NADP+ by A) oxidation reactions. B) reduction reactions. C) both oxidation and reduction reactions. D) neither oxidation nor reduction reactions.

Q: Whether an organism is classified as a photoheterotroph or a photoautotroph depends on its A) energy source. B) carbon source. C) oxygen requirements. D) carbon and energy sources.