Microbial sulphur cycle Flashcards
What are the most common oxidation states of sulfur?
-2,0,+2,+4,+6
Give three examples of inorganic materials the contain sulfur
Gypsum, epsomite, pyrite
Give the reaction for sulfur/sulfide oxidation
H2S -> S^0 -> SO4^2-
What organisms carry out the aerobic oxidation of sulfur/sulfide?
Sulfur chemolithotrophs
e.g. Thiobacillus
What organisms carry out the anaerobic oxidation of sulfur/sulfide?
Purple and green phototrophic bacteria and some chemolithotrophs
What is the reaction of anaerobic sulfur reduction?
S^0 -> H2S
What is the reaction of aerobic sulfate reduction?
SO4^2- -> H2S
What is the reaction of desulfurylation?
Organic S -> H2S
What is the ultimate product of sulfur/sulfide oxidation?
Sulfate
Give three examples of electron acceptors in the oxidation of sulfur/sulfide
Oxygen, nitrate, Fe(III)
Give an example of an organism that can oxidise sulfur/sulfide at neutral pH and describe it
Thioploca
Found in marine sediments and uses nitrate as e- acceptor
Moves between areas of high nitrate and areas of high sulphide
Why is it important that there are organisms that can oxidise sulfur/sulfide in acidic pH?
Bioleaching
Give five examples of sources of sulfide
Vents, springs, seeps, marine water, fresh water
Give an example of a sulfur/sulfide oxidising organism that uses oxygen as e- acceptor
Beggiatoa
Give an example of a sulfur/sulfide oxidising organism that uses nitrogen as e- acceptor
Thioploca
Describe cable bacteria in sulfide oxidation
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)
What does a sulfur accumulation act as and why?
An energy reserve
The flow of e- during oxidation releases energy by ATP synthesis
What does the reverse e- flow in oxidation result in?
Generation of reducing power (NADH/NADPH)
What organisms use the reverse e- flow of oxidation?
Autotrophs use NADPH for CO2 fixation
They have low growth yields
What organisms carry out sulfate reduction?
Sulfate reducing bacteria (SRB)
They are specialised anaerobes
Describe SRB
Most are deltaproteobacteria
What can some SRBs be?
Gram positive
Give four examples of e- donors for sulfate reduction
Fermantation products (e.g. acetate, lactate), glucose, aromatics, methane
What are the three stages of sulfate reduction?
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
What is the yield of steps one and two of sulfate reduction?
1 ATP
What is the yield of step three of sulfate reduction?
3 ATP
How can SRBs generate electron flow?
Some can disproportionate intermediate oxidate state sulfur compounds
Define disproportionation
Redox reaction where one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states
Give an example of disproportionation in relation to the reduction of sulfate
Oxidation of one S^0 to sulfate provides 6e- needed to reduce three S^0 to sulfide
Wha did Orphan et al (2001) find?
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
What is the reverse process of the depletion of C-13?
Methanogenesis
What happens as the SRB and methanotrophic arachaea are exposed to ion beam?
C-13 % decreases
Describe the type of bioremediation used in Budelco
Water was contaminated with metals/sulfate
SRBs remove metals and sulfate
Ethanol used as carbon source and e- donor
How long does the Shell-Budelco process take for a 9m^3 sludge blanket reactor?
7 hours
What are the four parts of the Shell-Budelco process?
Anaerobic reactor, aerobic reactor, TPS, sandfilter
Give two other examples of how SRBs can be used in bioremediation
Enzymatic reduction of metals and degradation of organics
