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MicroEco > Lecture 18 - Iron-Sulfur Cycling > Flashcards

Lecture 18 - Iron-Sulfur Cycling Flashcards

1
Q

How is sulfur oxide emitted into the atmosphere?

A

microbial processes | fossil fuel burning | volcanoes and host springs

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2
Q

What is the largest reservoir of sulfur on the planet? What form is sulfur in within this reservoir? Is it actively cycled?

A

ocean | sulfate | yes

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3
Q

Which sulfur reservoir is not actively cycled?

A

Earth’s crust

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4
Q

What form is sulfur in within the atmospheric sulfur reservoir?

A

sulfur oxide and hydrogen sulfide

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5
Q

What are the 4 processes of the sulfur cycle?

A

sulfur assimilation | sulfur mineralization | sulfur oxidation | sulfur reduction

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6
Q

What is sulfur assimilation?

A

taking sulfate (SO4) and incorporating it into biological molecules | requires 2 ATP

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7
Q

What is the predominant form of sulfur in the environment?

A

sulfate (SO4)

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8
Q

What kind of reaction (reduction or oxidation) does sulfur assimilation occur within the cell?

A

reduction reaction

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9
Q

What does “-SH” stand for?

A

organic sulfur

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10
Q

What is sulfur mineralization?

A

a metabolic reaction, opposite of assimilation process | releasing sulfur from organic molecules | anaerobic and aerobic environment

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11
Q

What do the process of sulfur assimilation and mineralization cycle sulfur between, since they are opposites?

A

organic and inorganic forms of sulfur

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12
Q

What is H2S?

A

hydrogen sulfide = toxic gas

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13
Q

What is sulfur oxidation?

A

H2S&raquo_space;> SO4 via oxidation reactions

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14
Q

What are the 2 ways sulfur is oxidized in sulfur oxidation? (aerobically)

A

H2S&raquo_space;> So (elemental sulfur) | So&raquo_space;> SO4 (results in acid)

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15
Q

Which step in sulfur oxidation results in acid mine drainage and why?

A

So&raquo_space;> SO4 because it’s really So + H2O&raquo_space;> SO4 + 2H+ and that mixed together results in sulfuric acid

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16
Q

How does the So&raquo_space;> SO4 reaction cause acid mine drainage? What is acid mine drainage useful in?

A

in low pH = causes metals to precipitate out | useful in metal recovery

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17
Q

What is a way that sulfur is oxidized anaerobically?

A

use NO3 as e- acceptor = end up producing calcium sulfate (gypsum)

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18
Q

What is photoautotrophic sulfur oxidation?

A

photoautotrophic organisms that can oxidize sulfur by using light energy

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19
Q

Which organisms are capable of photoautotrophic sulfur oxidation?

A

green and purple sulfur bacteria

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20
Q

Why are the green and purple sulfur bacteria an important group of organisms?

A

they remove sulfide from the environment and oxidize it to sulfur | H2S&raquo_space;> So

21
Q

What is sulfur reduction?

A

inhibited by oxygen | makes H2S = can cause metal corrosion

22
Q

What are the 3 ways sulfur is reduced?

A

sulfur assimilation | sulfur respiration | dissimilation

23
Q

What is sulfur respiration?

A

So&raquo_space;> H2S | uses acetate as one of the reactants

24
Q

What is sulfur dissimilation?

A

SO4&raquo_space;> H2S | uses methanol as one of the reactants

25
Q

In sulfur reduction, where do methanol and acetate come from? What does it mean?

A

carbon cycle from fermenter microbes | an anaerobic interaction between the sulfur reducing bacteria and the carbon-fermenting bacteria and methanogens

26
Q

What are 5 things sulfur is required for?

A

cysteine | methionine | vitamins | hormones | co-enzymes

27
Q

What can the sulfur cycle form in the environment?

A

acid rain | acid mine drainage | metal corrosion

28
Q

Even though iron is highly abundant in the Earth’s crust, why is it not readily used?

A

bioavailability is limited = not in the form cells can use it

29
Q

Why is iron important? What is it used for?

A

all cells need iron - used as co-factors in respiration and photosynthesis

30
Q

If all cells need iron, how do microbes attain it when the bioavailability of iron is limited?

A

cells have developed different ways of attaining iron

31
Q

Does iron only rely on cells to change form? Why or why not?

A

no it can change form chemically

32
Q

What are the two main processes in iron cycling?

A

iron oxidation | iron reduction

33
Q

What is iron oxidation?

A

Fe2 (ferrous iron)&raquo_space;> Fe3 (ferric iron) | generates low amounts of energy | aerobic, commonly seen under acidic conditions = leads to acid mine drainage

34
Q

What is the result of iron oxidation occuring in neutral conditions?

A

results in metal corrosion

35
Q

How do the green and purple phototrophic sulfur bacteria play a role in the iron cycle?

A

they are capable of using ferrous iron (Fe2) as an electron donor instead of oxygen to perform iron-based photosynthesis

36
Q

What hypothesis does iron-based photosynthesis help theorize?

A

planet wasn’t always oxygenated = anaerobic = iron-based photosynthesis may represent a type of photosynthesis that was present on the planet before transitioning to aerobic conditions

37
Q

What are the 2 main purposes/different reactions of iron reduction?

A

assimilation | energy generation

38
Q

What is iron assimilation?

A

taking iron and reducing it to be usable within a cell

39
Q

What complex does iron assimilation occur with?

A

siderophores

40
Q

What are siderophores?

A

compound that binds to iron secreted by microbes to transport iron

41
Q

How do siderophores help bacteria intake iron?

A

siderophore recognizes a surface receptor on cell = result in the reduction and transport of iron into cell

42
Q

What form of iron is commonly used by cells?

A

Fe2

43
Q

What is the energy generation part of iron reduction?

A

using ferric iron (Fe3) through anaerobic respiration

44
Q

What are the two ways cells generate energy using ferric iron (Fe3)?

A

direct attachment/contact | electron-shuttle

45
Q

What is iron reductase?

A

membrane-bound enzyme allowing direct access

46
Q

What is the direct attachment method bacteria use to reduce Fe3?

A

bacteria directly contacts with iron oxide surface = iron reductase reduces Fe3 to Fe2 = Fe2 used to make energy needed to take organic carbon and fix it into CO2 and water

47
Q

What is the electron shuttle method bacteria use to reduce Fe3?

A

molecule or protein that shuttles the electrons from the iron oxide surface (post iron reduction) to the cell

48
Q

What is a common electron shuttle, especially in soil environments?

A

humic acids

49
Q

What are the important things from the iron cycle?

A

green and purple sulfur bacteria | iron reduction for both assimilation and energy generation

MicroEco (10 decks)

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