Chapter 14 Lecture Outline Respiration, Lithotrophy, and Photolysis

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 2 Common Principles of Respiration, Lithotrophy and Photolysis Electron transport system (electron transport chain) Electron transfer reactions (oxidation-reduction reactions)  A is oxidized, B is reduced  Energy of electron flow powers the cell Storage of energy from electron transfer in form of an electrochemical potential (voltage) across the membrane Voltage potential includes a concentration gradient of ions (H +, Na + ) plus charge difference Voltage potential drives ATP synthesis and other processes

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 3 Electricity from Iron-Reducing Bacterium Soil bacteria commonly oxidize organic nutrients Geobacter metallireducens transfers electrons to iron ions (F 3+ ) via their pili Pili act as nanowires Can power an electrical clock

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 4 Respiration  Organic molecules are electron donors (oxidation of organic electron donors) Sugars, lipids, amino acids  Final electron acceptor is oxygen (aerobic respiration) or inorganic molecules (anaerobic respiration) Lithotrophy  Inorganic molecules are electron donors (oxidation of inorganic electron donors) Fe 2+, H 2  Final electron acceptor is oxygen or inorganic molecule Photolysis  Light capture coupled to splitting of H 2 S or H 2 O Distinction of Respiration, Lithotrophy and Photolysis

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 5 How does Fermentation fit in? Electrons passed to electron acceptors  Respiration Electrons passed to through electron transport system to inorganic acceptors  Aerobic respiration: O 2  Anaerobic respiration: nitrogen, sulfur compounds  Fermentation Electrons passed to organic receptors without electron transport system

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 6 Refresh Once More the Sources of Energy, Electrons, and Carbon Energy  photo- (light) vs. chemo- Electrons  litho- (inorganic) vs. organo- Carbon  auto- (CO 2 ) vs. hetero- (all else)

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 7 Electron Transport Systems Electron transport occurs on membranes  Electron acceptor usually present outside cell (exogenous) Needed in large quantities for respiration  Electron passage energy must be captured by cell cytoplasm Inner (cell) membrane of bacteria, archaea  Inner membrane of mitochondria, chloroplasts Selenium granule deposited at inner membrane

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 8 Members of an Electron Transport System (ETS) NADH or other electron donor Electrons Oxidoreductase protein complexes  Cytochromes Colored proteins Absorbance spectrum shifts with change in redox state Cytochrome C Oxidase detected in clinical diagnostic kits  Cofactors like FMN  Quinones  Terminal oxidase Terminal electron acceptor

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 9 The Respiratory ETS Electrons from NADH  O 2 release energy  Too much energy to capture in one step  Requires intermediates Multiple steps Common features in many ETS pathways  NADH Oxidase  Quinones  Cytochromes

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 10 Electron Transport is Coupled to Proton Transport Sequential electron transfer yields energy to pump ions across the membrane Most often H+ Proton concentration gradient is established Concentration gradient plus charge (chemiosmosis) difference creates proton motive force

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 11 The Proton Motive Force Energy of electron transport is captured  As a gradient across a membrane Gradient of protons  Charge and concentration of electrons Drives protons out of cell  Gradient of protons has charge, concentration Both tend to drive protons back into cell

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 12 The Chemiosmotic Hypothesis Electron transport system pumps protons out of the cell Resulting electrochemical gradient of protons drives conversion of ADP to ATP through ATP synthase

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 13 Processes Driven by Proton Motive Force ATP Synthase Uptake of nutrients Drug efflux pumps Flagellar rotation

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 14 ATP Synthase (ATPase) The F0 subunits rotate relative to the F1 complex F0 F1 ADP + Pi ATP Protons enter c subunits of the F0 complex Flux protons is coupled to converting ADP + P i to ATP

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 15 E. coli Respiratory ETS Animation: A Bacterial Electron Transport System Click box to launch animation

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 16 Proton Potential Creates ATP Animation: ATP Synthase Mechanism Click box to launch animation

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 17 Anaerobic Respiration Many environments lack oxygen  Gut, deep soil, deep ocean Less energy producing than aerobic respiration Use other terminal electron acceptors  Nitrogen compounds NO e - + 2H +  NO H 2 O 2 NO e - + 4H +  2 NO + 2H 2 O 2 NO + 2e - + 2H +  N 2 O + H 2 O N 2 O + 2e - + 2H +  N 2 + H 2 O NO e - + 8H +  NH H 2 O Funnels into nitrogen oxidation

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 18 Lithotrophy Reduced minerals serve as electron donors for an electron transport system Only prokaryotes can grow by metabolizing inorganic compounds without photosynthesis  Fill many key niches in ecosystems

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 19 Examples for Lithotrophy Nitrogen oxidation  Anaerobic ammonium oxidation plays major role in waste water treatment Sulfur oxidation  production of sulfuric acid  Supplemental to commercial mining Metal oxidation Hydrogenothrophy  Oxidation of H 2 by sulfur leads to H 2 S

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 20 Methanogenesis

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 21 Methanogenesis Reduction of CO 2 and other single carbon compounds to methane  Metabolized by methanotrophs Only observed in a special group of archaea  Methanogens Found in  Landfills Natural methane gas can be harvested  Intestine of cows and humans  Deep oceans

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 22 Do not Confuse Methanogens  Generate methane Methanotrophs  Oxidize (metabolize) methane Methylotrophs  Oxidize single C molecules other than methane such as methanol or methylamine

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 23 Phototrophy and Photolysis Phototrophy: all forms of energy yielding metabolism that involve absorption of light energy Photolysis: light absorption coupled to splitting an electron from a molecule Photosynthesis: photolysis with CO 2 fixation and biosynthesis

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 24 Photolysis Photoexcitation of a light absorbing pigment leads to electron transfer through an ETS Light-driven separation of electrons from a molecule Electron passes to quinols  From quinols to cytochromes  Energy of passage pumps H + outside membrane Photolytic ETS generates a proton potential and the reduced cofactor NADH Photolytic proton potential drives ATP synthase

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 25 Lightabsorbing Pigments Used in Prokaryots Chlorophyll (in cyanobacteria) Bacteriochlorophyll  In green and purple bacteria Caretenoid  Accessory pigment used by purple bacteria Conduct photolysis

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 26 Common Principle of Photolysis Membrane embedded chain of oxidoreductases and quinones Common design  Antenna system  Reaction center complex  ETS  Energy carriers

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. 27 Photolytic Electron Transport Chain Three systems  Photosystem I  Photosystem II  Oxygenic Z pathway Includes PSI and II components Molecular oxygen is generated Only in cyanobacteria (and green plants)