MIcro Bio Exam 4 reivew questions

Sulfur Cycle, Nitrogen Cycle

Which organisms are capable of sulfur oxidation?

Diverse members of Archaea and Bacteria

which is not a way microbial diversity is achieved?

Vertical gene transfer

What is gene loss?

Loss of an ancestral trait over time due to divergence

What is convergent evolution?

Independent evolution of similar traits in different lineages

What is horizontal gene transfer?

Exchange of homologous genes between unrelated organisms

What is a common electron donor in sulfur cycling?

hydrogen sulfide (H2S)

What are common electron acceptors in sulfur cycling?

Sulfur (S0) & Sulfate (SO₄²⁻)

Anaerobic respiration yields more energy than aerobic respiration.
True / False

False

Why does anaerobic respiration yield less energy than aerobic respiration?

Oxygen/water is the most electropositive electron acceptor

When do facultative aerobes switch to alternative electron acceptors?

When oxygen becomes limiting

What are some examples of alternative electron acceptors in facultative aerobes?

Fe³⁺ and Mn⁴⁺

What are sulfidic environments?

Anoxic environments with high hydrogen sulfide

What is not one of the 3 functional components included in the respiratory electron transport system?

oxidase

Anaerobic respiration can only be carried out by bacteria or archaea.
True / False

True

What is an obligate anaerobe?

Cannot respire using oxygen

What is a facultative aerobe?

Can grow with or without oxygen

What type of -troph performs anaerobic respiration?

Chemolithotroph & Chemoorganotroph

What is not a trait of an assimilative process in the sulfur cycle?

Excretion of reduced compounds

What is not a trait of an dissimilative process in the sulfur cycle?

Used for biosynthesis only

At the end of the dissimilative process, do compounds become part of biomass?

No, they are excreted

Is dissimilative process only a respiratory process?

Yes

What is DMSO?

Dimethyl sulfoxide

sulfate is ______ favorable as an electron acceptor than oxygen or nitrate?

Less

Full reduction of sulfate requires how many electrons?

8

What is hydrogen sulfide (H₂S)

A major volatile sulfur compound produced biologically and geochemically

What can sulfur-oxidizing chemolithotrophs (SOBs) oxidize?

S⁰ & HS⁻

What is the most abundant organic sulfur compound?

Dimethyl sulfide

Where is DMS primarily produced?

Marine environments

Sulfate-reducing bacteria use ______ and produce ______

Oxidized sulfur; H₂S

Sulfur-oxidizing bacteria use ______ and produce ______.

Reduced sulfur; sulfate

Which of the following describes Beggiatoa, a genus of bacteria known for forming dense white mats in sulfur-rich environments?

Filamentous, gliding bacteria composed of many short cells attached end to end.

Who drew Beggiatoa?

Winogradsky

What positions Beggiatoa where H₂S and O₂ meet?

Gliding motility

Which of the following best describes the characteristics of Beggiatoa spp.?

They are Gammaproteobacteria that oxidize sulfide, store internal sulfur granules, and are aerobic chemolithotrophs.

Which of the following best describes the traits of Sulfolobus acidocaldarius

They are members of the Thermoprotei class that obtain energy by oxidizing sulfur to sulfate

Which of the following statements about Thioploca is FALSE?

They are single-celled, non-motile bacteria that thrive in dry, alkaline soil

Which of the following best describes the characteristics of Thiothrix?

A filamentous chemolithotroph that forms filamentous groups together at their ends by a holdfast and is an obligated aerobic mixotroph

What is the purpose of a holdfast

Attachment in high-flow environments to provide H2S

What is a mixotroph?

Combines autotrophy and heterotrophy

Which of the following best describes the traits of Thiovulum

Found in freshwater and marine habitats where sulfide-rich muds meet oxic zones, it controls the flow of nutrients to cells by rotating around the flagellar axis within a slimy veil to regulate sulfide and oxygen gradients.

Which of the following best describes the traits of Thiomargarita

Both A and B are correct.

Where do obligate chemolithotrophs perform the Calvin cycle?

Carboxysomes

Facultative chemolithotrophs grow either ______ or ______.

Chemolithotrophically or chemoorganotrophically

Complete oxidizers convert acetate to:

CO₂

Incomplete oxidizers cannot convert acetate to

CO₂

Which of the following groups consists entirely of complete oxidizers?

Desulfobacter, Desulfococcus, Desulfosarcina, and Desulfonema

Which of the following groups of sulfate-reducing bacteria consists entirely of incomplete oxidizers

Desulfovibrio, Desulfomonas, Desulfotomaculum, and Desulfobulbus

Which of the following is NOT an alternative metabolic pathway or characteristic for dissimilative sulfate reducers

Most species are obligate aerobes that require high atmospheric oxygen to fix nitrogen

What is a function of hydrothermal vents

Support lithoautotrophic-based ecosystems

Which of the following describes the diverse communities that develop near hydrothermal vents?

Invertebrates (large tube worms, clams, and mussels) that often rely on symbiotic sulfur-oxidizing bacteria for nutrition.

Which of the following describes the purpose of TSI (triple sugar iron) agar?

Used to identify microbes, it can show fermentation with acid and/or gas production, as well as the reduction of sulfur.

Which of the following explains why a black color forms in TSI (Triple Sugar Iron) agar?

The production of hydrogen sulfide from either protein degradation or thiosulfate reduction.

Which of the following describes the purpose of Hektoen Enteric (HE) Agar?

A selective and differential medium used in clinical microbiology to isolate and differentiate pathogenic enteric bacteria, particularly Salmonella and Shigella species, from fecal, food, and environmental samples.

What does HE agar contain?

Sodium thiosulfate and ferric ammonium citrate

Salmonella cannot ferment sugars.
True / False

True

Sulfur oxidation produces H⁺ and acidifies surroundings.
True / False

True

Why do organisms attach to S⁰

It is insoluble

Which of the following defines MIC (microbial induced corrosion)

The deterioration of metals, alloys, and concrete caused by the metabolic activity of microorganisms, such as bacteria or fungi, which form biofilms on the surface.

Sox systems do what

Oxidize sulfur to sulfate

Which of the following represents the 4 key proteins in the Sox system responsible for the oxidation of reduced sulfur compounds?

SoxXA, SoxYZ, SoxB, and SoxCD (sulfur dehydrogenase)

SoxCD function?

Removes six electrons

SO₄²⁻ is energetically more favorable than oxygen.
True / False

False

H₂ is used as an electron donor by nearly all species.
True / False

True

Dissimilative reduction generates:

Proton motive force

SO₄²⁻ must be activated by ______.

ATP sulfurylase

Which of the following correctly completes the description of assimilative reduction?

Phosphate is added to APS to form PAPS, which is then reduced to sulfite.

In dissimilative reduction, which of the following correctly describes the direct reduction step involving APS?

In dissimilative reduction, sulfate in APS is reduced directly to produce sulfite.

Common electron acceptors in anaerobic respiration include:

Inorganic nitrogen compounds

A common alternative electron acceptor is:

Nitrate

Which of the following correctly describes the steps when nitrate is further reduced during denitrification?

Nitrate → Nitrite → nitric oxide → nitrous oxide → dinitrogen (N₂)

Nitrogen fixation is performed by:

Bacteria and Archaea

Which of the following describes the purpose of dissimilative reduction in the Nitrogen Cycle?

Conserves energy by using nitrate as a terminal electron acceptor in anaerobic respiration, where the product is a small molecule of excreted from the cell.

Dissimilative nitrogen reduction occurs in:

Anaerobic microbes

Nitrogen fixation is a respiratory process.
True / False

False

Which of the following describes nifH?

Also known as nitrogenase, it is the enzyme responsible for nitrogen fixation.

Which of the following describes the process of ammonification?

breakdown of organic nitrogen into ammonium

Anammox is:

NO₂⁻ + NH₃ → N₂

Nitrogen respiratory processes include:

All of the above

Oligotrophic means:

Low nutrients

How is the nitrogenase enzyme protected in obligate aerobes, given its extreme sensitivity to oxygen?

Removal by respiration, oxygen-retarding slime layers, and anoxic heterocyst formation.