L20W10_MIC105_Sulfur

L20W10_MIC105_Sulfur - * Sulfur Cycle Reactions Organic...

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2/26/2010 1 Sulfur Cycle Reactions Organic Sulfur H 2 S S 0 SO 4 2- assimilation (assimilatory reduction) Desulfurylation (breakdown of sulfur-containing organics) (hydrogen sulFde) sulfur reduction Sulfate reduction SulFde/Sulfur oxidation (sulfate) *
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2/26/2010 2 Inorganic sulfur compounds serve as electron acceptors in anaerobic respiration , which is carried out by sulfate reducing bacteria This is an energy-generating process Differs from assimilatory sulfate reduction , which is the use of sulfate as a source of S for biosynthesis End product of respiratory sulfate/ sulfur reduction is H 2 S, which is excreted from cells Sulfate/sulfur reducing bacteria *
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2/26/2010 3 All known sulfate reducers are Bacteria except Archeoglobus , a hyperthermophilic Euryarchaeote Some Bacteria and Archaea are capable of sulfur (but not sulfate) reduction Bacterial sulfate/sulfur reducers are mainly members of the δ -Proteobacteria. e.g. Desulfovibrio One genus of Gram positive endosporeforming sulfate reducers: Desulfotomaculum Sulfate reducing microbes *
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2/26/2010 4 Obligate anaerobes, many are motile Most use H 2 , lactate and pyruvate as electron donors Some use alcohols or other fatty acids, even benzoate or hydrocarbons as electron donors Some can also respire with nitrate as terminal electron acceptor Some can ferment in the absence of sulfate Sulfate reducing bacteria *
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2/26/2010 5 Some grow as lithoautotrophs using H 2 as electron donor, sulfate as electron acceptor, and CO 2 as sole carbon source Most of the autotrophic sulfate reducers use the reductive acetyl-CoA pathway * to Fx CO 2 ... but there is at least one sulfate reducer that is known to use the reverse TCA cycle * *see Lecture 14 Sulfate reducing bacteria *
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2/26/2010 6 Widespread in anoxic aquatic and terrestrial environments including marine sediments Can be enriched in anoxic medium containing lactate and ferrous iron SulFde reacts with ferrous iron to form insoluble ferrous sulFde (indicator and detoxiFcation) Sulfate reducing bacteria *
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2/26/2010 7 Sulfate reducing bacteria: enrichment and isolation
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Sulfate reducing bacteria: morphology Desulfovibrio Desulfomonas Desulfonema Desulfosarcina
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2/26/2010 9 Sulfate reduction is less energetically favorable than respiration with O 2 or nitrate Sulfate reducing bacteria: energetics * Glucose + 6 O 2 -> 6 CO 2 + 6 H 2 0 Δ G o ’ = -2830 kJ/mol Glucose + 12 NO 3 - -> 6 CO 2 + 12 NO 2 - + 6 H 2 0 Δ G o ’ = -1926 kJ/mol 4 H 2 + SO 4 2- + H + -> HS - + 4 H 2 0 Δ G o ’ = -152 kJ/mol
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2/26/2010 10 Reduction of SO 4 2- to H 2 S is an 8 electron reduction and the process takes place in multiple steps The reduction of sulfate Frst requires activation by ATP to form adenosine phosphosulfate (APS).
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L20W10_MIC105_Sulfur - * Sulfur Cycle Reactions Organic...

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