Microbial sulphur cycle

Question 1

What are the most common oxidation states of sulfur?

Answer 1

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

Question 2

Give three examples of inorganic materials the contain sulfur

Answer 2

Gypsum, epsomite, pyrite

Question 3

Give the reaction for sulfur/sulfide oxidation

Answer 3

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

Question 4

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

Answer 4

Sulfur chemolithotrophs
e.g. Thiobacillus

Question 5

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

Answer 5

Purple and green phototrophic bacteria and some chemolithotrophs

Question 6

What is the reaction of anaerobic sulfur reduction?

Answer 6

S^0 -> H2S

Question 7

What is the reaction of aerobic sulfate reduction?

Answer 7

SO4^2- -> H2S

Question 8

What is the reaction of desulfurylation?

Answer 8

Organic S -> H2S

Question 9

What is the ultimate product of sulfur/sulfide oxidation?

Answer 9

Sulfate

Question 10

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

Answer 10

Oxygen, nitrate, Fe(III)

Question 11

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

Answer 11

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

Question 12

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

Answer 12

Bioleaching

Question 13

Give five examples of sources of sulfide

Answer 13

Vents, springs, seeps, marine water, fresh water

Question 14

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

Answer 14

Beggiatoa

Question 15

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

Answer 15

Thioploca

Question 16

Describe cable bacteria in sulfide oxidation

Answer 16

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)

Question 17

What does a sulfur accumulation act as and why?

Answer 17

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

Question 18

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

Answer 18

Generation of reducing power (NADH/NADPH)

Question 19

What organisms use the reverse e- flow of oxidation?

Answer 19

Autotrophs use NADPH for CO2 fixation
They have low growth yields

Question 20

What organisms carry out sulfate reduction?

Answer 20

Sulfate reducing bacteria (SRB)
They are specialised anaerobes

Question 21

Describe SRB

Answer 21

Most are deltaproteobacteria

Question 22

What can some SRBs be?

Answer 22

Gram positive

Question 23

Give four examples of e- donors for sulfate reduction

Answer 23

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

Question 24

What are the three stages of sulfate reduction?

Answer 24

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

Question 25

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

Answer 25

1 ATP

Question 26

What is the yield of step three of sulfate reduction?

Answer 26

3 ATP

Question 27

How can SRBs generate electron flow?

Answer 27

Some can disproportionate intermediate oxidate state sulfur compounds

Question 28

Define disproportionation

Answer 28

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

Question 29

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

Answer 29

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

Question 30

Wha did Orphan et al (2001) find?

Answer 30

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

Question 31

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

Answer 31

Methanogenesis

Question 32

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

Answer 32

C-13 % decreases

Question 33

Describe the type of bioremediation used in Budelco

Answer 33

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

Question 34

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

Answer 34

7 hours

Question 35

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

Answer 35

Anaerobic reactor, aerobic reactor, TPS, sandfilter

Question 36

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

Answer 36

Enzymatic reduction of metals and degradation of organics