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EART21102 Environmental Microbiology > Microbial sulphur cycle > Flashcards

Microbial sulphur cycle Flashcards

1
Q

What are the most common oxidation states of sulfur?

A

-2,0,+2,+4,+6

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2
Q

Give three examples of inorganic materials the contain sulfur

A

Gypsum, epsomite, pyrite

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3
Q

Give the reaction for sulfur/sulfide oxidation

A

H2S -> S^0 -> SO4^2-

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4
Q

What organisms carry out the aerobic oxidation of sulfur/sulfide?

A

Sulfur chemolithotrophs
e.g. Thiobacillus

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5
Q

What organisms carry out the anaerobic oxidation of sulfur/sulfide?

A

Purple and green phototrophic bacteria and some chemolithotrophs

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6
Q

What is the reaction of anaerobic sulfur reduction?

A

S^0 -> H2S

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7
Q

What is the reaction of aerobic sulfate reduction?

A

SO4^2- -> H2S

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8
Q

What is the reaction of desulfurylation?

A

Organic S -> H2S

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9
Q

What is the ultimate product of sulfur/sulfide oxidation?

A

Sulfate

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10
Q

Give three examples of electron acceptors in the oxidation of sulfur/sulfide

A

Oxygen, nitrate, Fe(III)

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11
Q

Give an example of an organism that can oxidise sulfur/sulfide at neutral pH and describe it

A

Thioploca
Found in marine sediments and uses nitrate as e- acceptor
Moves between areas of high nitrate and areas of high sulphide

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12
Q

Why is it important that there are organisms that can oxidise sulfur/sulfide in acidic pH?

A

Bioleaching

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13
Q

Give five examples of sources of sulfide

A

Vents, springs, seeps, marine water, fresh water

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14
Q

Give an example of a sulfur/sulfide oxidising organism that uses oxygen as e- acceptor

A

Beggiatoa

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15
Q

Give an example of a sulfur/sulfide oxidising organism that uses nitrogen as e- acceptor

A

Thioploca

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16
Q

Describe cable bacteria in sulfide oxidation

A

Long filamentous bacteria that mediates sulfide oxidation across scales of cms by long distance e- flow
Role in preventing seasonal accumulation of sulfide (too much is poisonous)

17
Q

What does a sulfur accumulation act as and why?

A

An energy reserve
The flow of e- during oxidation releases energy by ATP synthesis

18
Q

What does the reverse e- flow in oxidation result in?

A

Generation of reducing power (NADH/NADPH)

19
Q

What organisms use the reverse e- flow of oxidation?

A

Autotrophs use NADPH for CO2 fixation
They have low growth yields

20
Q

What organisms carry out sulfate reduction?

A

Sulfate reducing bacteria (SRB)
They are specialised anaerobes

21
Q

Describe SRB

A

Most are deltaproteobacteria

22
Q

What can some SRBs be?

A

Gram positive

23
Q

Give four examples of e- donors for sulfate reduction

A

Fermantation products (e.g. acetate, lactate), glucose, aromatics, methane

24
Q

What are the three stages of sulfate reduction?

A

Sulfate is stable so is activated with ATP (gives Adenosine phosphosulfate)
APS reduced to sulfite by APS reductase
Sulfite reduced to sulfide by sulfite reductase

25
Q

What is the yield of steps one and two of sulfate reduction?

A

1 ATP

26
Q

What is the yield of step three of sulfate reduction?

A

3 ATP

27
Q

How can SRBs generate electron flow?

A

Some can disproportionate intermediate oxidate state sulfur compounds

28
Q

Define disproportionation

A

Redox reaction where one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states

29
Q

Give an example of disproportionation in relation to the reduction of sulfate

A

Oxidation of one S^0 to sulfate provides 6e- needed to reduce three S^0 to sulfide

30
Q

Wha did Orphan et al (2001) find?

A

Methane, which can be used as an e- acceptor, can be metabolised first, indicated by the depletion of C-13
Metabolic activity and determination of identity are simultaneous

31
Q

What is the reverse process of the depletion of C-13?

A

Methanogenesis

32
Q

What happens as the SRB and methanotrophic arachaea are exposed to ion beam?

A

C-13 % decreases

33
Q

Describe the type of bioremediation used in Budelco

A

Water was contaminated with metals/sulfate
SRBs remove metals and sulfate
Ethanol used as carbon source and e- donor

34
Q

How long does the Shell-Budelco process take for a 9m^3 sludge blanket reactor?

A

7 hours

35
Q

What are the four parts of the Shell-Budelco process?

A

Anaerobic reactor, aerobic reactor, TPS, sandfilter

36
Q

Give two other examples of how SRBs can be used in bioremediation

A

Enzymatic reduction of metals and degradation of organics

EART21102 Environmental Microbiology (9 decks)

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