Metabolism LecturesRespiration ReviewAnaerobic RespirationMetabolic Classification Based on Oxygen ConcentrationsDiversity of electron acceptors for respirationPowerPoint PresentationModularity of electron transport chains what do most of these have in common?Example 1. Nitrate reductionFigure 24.19 Nitrogen cycleNitrate reducing bacteriaDissimulative NO3- reductionDenitrification by Pseudomonas stutzeriSlide 13Dissimilatory nitrate reduction: BiochemistryNitrate vs. oxygen vs. denitrification respirationHow much energy is made by reducing nitrate to nitrite with NADH?Example 2. Arsenate reductionArsenic respiring bacteria and human healthShewanella sp. strain ANA-3Example 3. IronIron oxide reducing bacteriaChemolithotrophy and Oxidation of Inorganic MoleculesGeological, biological, and anthropogenic sources of reduced inorganic compounds supporting chemolithotrophsEnergy yields from various inorganic electron donors:Oxidation of sulfur-compoundsLecture SummaryMetabolism LecturesOutline:Part I: FermentationsPart II: RespirationPart III: Metabolic DiversityLearning objectives are:Learn about anaerobic respiratory metabolisms.How can an inorganic compound be use as an energy source.Respiration Review2NADHQ2NAD+2H+2H+H+H+O24H+2 H2OH+H+percytolow Eo’ electron flow hi Eo’ATPADP3H+Electron TowerAnaerobic RespirationAnaerobic metabolism is of clinical importance:–Deep tissue infections can lead to abscess formation, foul-smelling pus, and tissue destructionUses inorganic and organic molecules other than oxygen as terminal electron acceptors– Extensive list of electron acceptors–oxyanions, metals, metal oxides, organic acids, inorganicEnergy and carbon sources are diverse–Metabolic Classification Based on Oxygen ConcentrationsPoints of reference:–Atmospheric oxygen is ~21% (v/v) (or 2.1 x 105 parts per million)–Low solubility in water: up to 14 parts per million (T and P dependent)Remember metabolic classifications:–Strict aerobe (non-fermentative, respires oxygen)–Strict anaerobe (sensitive to oxygen)–Facultative anaerobe: (fermentative and/or respiration)–Microaerophilic (or microaerophile)40:1 anaerobes to facultative anaerobes in human fecesDiversity of electron acceptors for respirationOrganic compounds:–Eg. fumarate, dimethylsulfoxide (DMSO), Trimethylamine-N-oxide (TMAO)Inorganic compounds:–Eg. NO3-, NO2-, SO42-, S0, SeO42-, AsO43-Metals:–Eg. Fe3+, Mn4+, Cr6+Minerals/solids:–Eg. Fe(OH)3, MnO2Gasses:–Eg. NO, N2O, CO2Why is there so much diversity?How can prokaryotes accomplish this?Dehydrogenase:LactateSuccinateFormateNADHGlycerophosphateHydrogenaseMQUQfumarateCyt b, Fe/S, FADFumarate reductaseCyt b, Fe/S, MoDMSODMSO reductaseCyt b, Fe/S, MoTMAOTMAO reductaseCyt b, Fe/S, MoNO3-Nitrate reductaseElectron donor modules Electron acceptor “modules”Answer:Modularity of electron transport chainswhat do most of these have in common?Example 1.Nitrate reductionFigure 24.19 Nitrogen cycleFigure 24.19 Nitrogen cycle78% N2Nitrate reducing bacteriaNitrate reducing bacteriaContribute to denitrification (removal of ?)Beneficial process for sewage treatment plantsNitrogenous waste good food for algaeDissimilatory nitrate reduction widespread in microbes–Used for making energy via oxidative phosphorylationNitrate is a strong oxidant similar to oxygenSome microbes can take Nitrate all the way to Nitrogen gas:–Pseudomonas stutzeri–E0’ +0.74 V compared to +0.82 for 1/2O2/H2O–How many electrons are used from NO3- to N2?Dissimulative NO3- reductionDenitrification by Pseudomonas stutzeriDenitrification by Pseudomonas stutzeriFour terminal reductases–Nap: Nitrate reductase (Mo-containing enzyme)–Nir: Nitrite reductase–Nor: Nitric oxide reductase–N2or: Nitrous oxide reductaseAll can function independently but they operate in unisonDissimilatory nitrate reduction: BiochemistryElectron donor: lactate, formate, H2, others–Uses special dehydrogenases for these.Enzymes are membrane-boundPeriplasmic nitrate reductases (NapA) contains a molybdenum cofactorCoupled to the generation of PMFATP synthesized by oxidative phosphorylationNitrate vs. oxygen vs. denitrification respiration oxygennitritedenitrificationHow much energy is made by reducing nitrate to nitrite with NADH?Nitrate= N(x) + 3O2-  x + 3(-2) = -1  x=Nitrite= N(x) + 2O2-  x + 2(-2) = -1  x=Determining oxidation state of N and # of electrons:?e-Nitrate(NO3-)Nitrite(NO2-)?NADH?NAD+example?ATPWe only need to oxidize ______ NADH for this:NADH + H+NAD+ + 2H+ + 2e-What’s reduce and oxidized?Find ∆Eo’ of nitrate/nitrite and NAD+/NADH Use Nernst Eq to find ∆Go’Example 2.Arsenate reductionArsenate  arseniteEo’+0.139 Vhttp://phys4.harvard.edu/~wilsonArsenic respiring bacteria and human healthArsenic is mainly a groundwater pollutantAffects ~140 million people among ~70 countriesArsenate (As[V]):–Like phosphate: H2AsO4-–Affects ATP synthesisArsenite (As[III]): H3AsO3–More toxic than As(V)–Binds proteins–Causes DNA damageMicrobes respire arsenate and make arseniteMedical Geology problemShewanella sp.strain ANA-32As(V)2As(III)As2S3LactateAcetate+CO2Dividing cellIsolation of strainRespiring O2Respiring AsO43-Example 3. Iron2Fe(III)2Fe(II)NADH2 NAD+c-hemeQH2QCMOMFeIII-oxideIron oxide reducing bacteriaExamples:–Geobacter, Shewanella, RhodoferraxHow do they do it?Chemolithotrophy and Oxidation of Inorganic MoleculesA. A pathway used by a small number of microorganisms called chemolithotrophsB. Produces a significant but low yield of ATPC. The electron acceptor is commonly O2, some others include sulfate and nitrateD. The most common electron donors are hydrogen, reduced nitrogen compounds, reduced sulfur compounds, and ferrous iron (Fe2+)Geological, biological, and anthropogenic sources of reduced inorganic compounds supporting chemolithotrophsTypical habitats of chemolithotrohs:Near the interface ofoxic/anoxic conditionsEnergy yields from various inorganic electron donors:Oxidation of sulfur-compoundsE.g.: Sulfur oxidizing Thiobacillii–Thiobacillus thiooxidans Thiobacillus ferrooxidansProduces sulfuric acid (H2SO4)–Acidification of soil–Dissolution of minerals, e.g. CaCO3Reactions ∆G˚’ kJ/mol H2S + 2 O2 >>> SO42- + 2H+ -798.2 HS- + 1/2O2 + H+ >>> S0 + H2O -209 S0 + H2O + 1.5 O2 >>> SO42- + 2H+ -587 S2O32-