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Fermentation: Catabolism of carbon in the absence of a terminal electron acceptor (like O 2 ) for electron transport cha

Fermentation: Catabolism of carbon in the absence of a terminal electron acceptor (like O 2 ) for electron transport chain. Compare the D E h for putting electrons onto O 2 vs. lactate. The unusual fermentation of oxalate by Oxalobacter formigenes.

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Fermentation: Catabolism of carbon in the absence of a terminal electron acceptor (like O 2 ) for electron transport cha

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  1. Fermentation: Catabolism of carbon in the absence of a terminal electron acceptor (like O2) for electron transport chain

  2. Compare the DEh for putting electrons onto O2 vs. lactate

  3. The unusual fermentation of oxalate by Oxalobacter formigenes Thank goodness for this hard-working anaerobe in your gut: it degrades oxalate from amino acid catabolism, coffee, tea, fruits, veggies… and helps prevent kidney stones!! You can lose it by taking doxycycline and other antibiotics, but can regain it by… guess how?

  4. And now for something completely different!

  5. Photosynthesis and Autotrophy I. Photosynthesis A. General Aspects B. Classes of Photosynthetic Bacteria C. Mechanism of Photosynthesis 1. Anoxygenic Photosynthesis 2. Oxygenic Photosynthesis D. Halobacterium (light-driven H+ pump) II. Autotrophy A. General Aspects B. Types of Autotrophic Pathways

  6. PHOTOSYNTHESIS (Photoautotrophy) Excited state X CO2 NADP+ photon e- CH2O NADPH Ground state

  7. PHOTOAUTOTROPHY: 2 reactions 1. LIGHT  CHEMICAL ENERGY (ATP) 2. CO2 reduction → Organic compounds

  8. Phototrophic Prokaryotes: the metabolic menu Group Reducing power Oxidized product Purple nonsulfur bacteria H2, reduced organic Oxidized organics Purple sulfur bacteria H2S SO4-2 Green sulfur bacteria H2S SO4-2 Green non sulfur bacteria* H2S SO4-2 Heliobacteria** Lactate, organics Oxidized organics Cyanobacteria H2O O2 Prochlorophytes***H2O O2 *Most ancient? **Gram positive, heterotrophs ***Related to cyanobacteria

  9. Three types of photochemical energy capturing systems in microorganisms: • Carotenoid-based light-capturing system that is structurally similar to rhodopsin in eyes. In halophilic Archaea. • Anoxygenic (uses chlorophyll, no O2 made) • Oxygenic (uses chlorophyll, splits water, generates oxygen)

  10. Carotenoid-based (bacteriorhodopsin) -no chlorophyll, no metals: protein with G-protein coupled receptor-like structure plus chromophore (retinal) -chromophore is a long-chain hydrocarbon with extensive conjugation -ancient protection for oxygenic phototrophs against toxic O2 -light-powered ion transfer Nagel et al. 2005. Mechanics of Biolenergetic Membrane Proteins 33: 863

  11. Photosystems do not absorb at short enough wavelengths to split water, so must get e-’s somewhere else. Cyclic: electrons run in closed circuit

  12. Photosystems can take light energy strong enough to split water. Non-cyclic (although cyclic can occur)

  13. Chlorophyll: Light Harvesting Molecule Porphyrin (like heme in cytochromes, but Mg instead of Fe) Bacteriochlorophyll: Absorbs at ~700 nm; allows light harvesting at depths where light is low and environment is anoxic Not enough energy to extract e- from H2O; must use H2S instead Eventually, chlorophyll evolved. Utilizes a short enough wavelength (680 nm) to split H2O and generate O2.

  14. Consequence of oxyenic photosynthesis in evolution: • *DNA absorbs UV at 260 nm; mutations occur • *Some exant organisms are resistant to damaging radiation • (e.g. Deinococcus radiodurans: survives 100 rad while 10 rads kills us… D. radiodurans is resistant to chromosome shattering and mutation) • O2 is a reactive molecule: ·O2- H2O2 OH · • At first, protected by Fe+2 (ferrous iron): Fe+2 + O2 FeOH3 Banded iron formations from Wittenoom Gorge in Australia

  15. Consequence of oxyenic photosynthesis in evolution: • Bacteria began evolving carotenoids: protection against singlet oxygen; convert to less toxic state • Eventually (at least 2 billion years ago), used up ferrous iron • Accumulation of O2 in atmosphere • O2 + sun (UV radiation) → O3 (ozone) • Ozone screened out wavelengths below 290 nm • - Life could evolve on land, because water no longer necessary to screen out damaging/mutagenic UV radiation

  16. Production of Reactive Oxygen Species (ROS) During normal cellular respiration, oxygen is reduced to water and highly reactive superoxide ( ·O2- ). Reactive oxygen species react with nucleic acids, sugars, proteins and lipids - eventually leading to molecular degradation.

  17. Cellular Defense Mechanisms Prevent ROS Buildup. • Due to the oxygen rich environment in which proteins exist, reactions with ROS are unavoidable. - Superoxide dismutase, catalase, and glutathione peroxidase are natural antioxidants present in organisms which eliminate some ROS. Other molecules are antioxidants too (e.g. ascorbic acid, or Ignose/Godnose!) - Glutathione peroxidase catalyzes the reduction of peroxide by oxidizing glutathione (GSH) to GSSG.

  18. Nutrient upwelling (El Nino) = phytoplankton blooms Detection of algal blooms from satellites via remote sensing: relies on reflected spectral properties of chlorophylls.

  19. Photosynthesis in the open oceans Compared to freshwater, nutrients (N, P, Fe) are limiting. Fewer cells found than in freshwater (only 106/mL prokaryotes and 104 eukaryotes) Because oceans are huge, collective O2 production and CO2 fixation there is a major contributor to Earth’s carbon balance. Influence food chain, global climate Many marine microbes use light to drive ATP synthesis. Photic zone = upper 300 meters Oxygenic and anoxygenic photosynthesis Chlorophylls a and b (cyanobacteria and relatives; algae) Proteorhodopsin (very similar to bacteriorhodopsin but Bacteria, not Archaea)

  20. Phototrophic Primary Producers (red = chlorophyll)

  21. Phototrophic Prokaryotes: • Purple nonsulfur bacteria • Green nonsulfur • Purple sulfur bacteria (sulfur inside cell) • Green sulfur bacteria (sulfur outside cell • Heliobacteria (G+ relatives of Clostridium, endospores, N2-fixation) 5. Cyanobacteria • Prochlorophytes • Halobacterium-type Domain Bacteria 1 group of “photocapable” prokaryotes in the Domain Archaea (the halobacteria = extreme halophiles [salt-loving])

  22. Photosynthetic Prokaryotes Group Reducing power Oxidized product Purple nonsulfur bacteria H2, reduced organic Oxidized organics Purple sulfur bacteria H2S SO4-2 Green sulfur bacteria H2S SO4-2 Green non sulfur bacteria H2S SO4-2 Heliobacteria* Lactate, organics Oxidized organics Cyanobacteria H2O O2 Prochlorophytes**H2O O2 • *Gram positive, heterotrophs • **Related to cyanobacteria

  23. Chlorophyll Diversity Different absorbance maxima = different niches… e.g. lower or higher in water column. Chlorophyll (cyanobacteria) = 680 nm Bchl a (purple bacteria) = 805, 870

  24. Structure of bacteriochlorophylls

  25. Accessory pigments:Carotenoids

  26. Accessory pigments:Phycobilins

  27. Photosynthetic Membranes Reaction center chlorophyll -few -convert light energy to ATP Light harvesting chlorophyll -many - “antenna” -captures “faint signal” of low light environments Accessory pigments Carotenoids Phycobilins

  28. … light harvesting complex in cyanobacteria, plants

  29. Mechanism of Photosynthesis1) Anoxygenic Photosynthesis • Cyclic • Your text: Fig. 17.14 , 17.15, and 17.18 • Purple Bacteria • Green Bacteria • Heliobacteria

  30. Purple Bacteria (within phylum Proteobacteria) • photosynthetic membranes are lamellae or tubes with the plasma membrane • bacteriochlorophyll a or b • accessory pigments are purple colored carotenoid pigments (see Fig. 12.5 in your text) • may live as photoheterotrophs two types: 1. sulfur 2. nonsulfur

  31. Green Bacteria • photosynthetic membranes are vesicles attached to but not continuous with the plasma membrane • bacteriochlorophyll c, b, or e (small amount of a in LH and RC) • accessory pigments are yellow to brown-colored carotenoids • two types: 1. sulfur (green sulfur bacteria phylum) 2. nonsulfur (green nonsulfur bacteria phylum)

  32. Heliobacteria • plasma membrane only (no specialized photosynthetic membranes) • bacteriochlorophyll g • Photoheterotrophs: require organic carbon • These are the only Gram-positive photosynthetic bacteria

  33. Electron donors: H2S, Fe2+, S0, etc.

  34. Anoxygenic Photosynthesis strong e- donor Purple bacteria

  35. Purple bacteria Cyclic NAD(P)H and ATP can be generated by PMF

  36. Many cyanobacteria can use H2S as an electron donor for anoxygenic photosynthesis. Elemental sulfur globules outside filamentous cyanobacterium Oscillatoria limnetica

  37. Purple bacterium (Chromatium): internal sulfur deposits Green bacterium (Chlorobium): external sulfur deposits

  38. Variation on the Theme ATP & NAD(P)H ATP only ATP only * * * Off to supply reducing power for CO2 fixation via reverse citric acid cycle

  39. Green Sulfur Bacteria (Chorobium, Chlorobaculum, Prosthecochloris) Aquatic, anoxic environments Most are facultative heterotrophs; strict autotrophy requires reverse TCA cycle Have chlorosomes: very efficient at light harvesting so live at great depths May form consortia – aggregates of cells that have differing metabolic duties; chemotrophic and phototrophic (epibiont) components. Example: Chlorochromatium aggregatum (not a formal taxonomic name because not a single species)

  40. Green Non Sulfur Bacteria (Choroflexus) Filamentous, form microbial mats with cyanobacteria in neutral to alkaline hot springs Like Green Sulfur Bacteria: has chlorosomes But reaction center of in cell membrane is like purple bacteria Earliest known photosynthetic bacterium: perhaps reaction center first, chlorosome later by HGT Most are facultative heterotrophs; CO2 fixation requires hydroxypropionate pathway (unique to very ancient organisms)

  41. Light harvesting complex in green photosynthetic bacteria (both sulfur and non-sulfur) Chlorosome is a giant antenna: Bchl c, d, or e BP = baseplate (proteins) LH = light harvesting complex (Bchl a) RC = reaction center (Bchl a)

  42. Chlorosomes (EM, stained dark)-in green sulfur bacteria-lie along the inside of cytoplasmic membrane-proteinaceous (nonlipid) membrane-each vesicle contains ~ 10,000 bacteriochlorophyll c molecules in tubes/rods-chlorosomes transmit energy via subantenna of bacteriochlorophyll a.

  43. Mechanism of PhotosynthesisOxygenic Photosynthesis • Photosystems I & II • Noncyclic • Your text, Fig. 17.19 • Cyanobacteria • Algae (protists) • Plants

  44. Cyanobacteria (phylum contains cyanobacteria and prochlorophytes) • Synechococcus, Oscillatoria, Nostoc, Anabaena • photosynthetic mebranes are multilayered lamellae • formerly called “blue-green algae” but now known to be prokaryotic and possess peptidoglycan • chlorophyll a only • accessory pigments are carotenoids and phycobilin proteins • Photosystem I and II are present (oxygenic photosynthesis) • Autotrophs • Gas vesicles frequent • Some are filamentous, N2 fixing (heterocysts)

  45. Lake Mendota up close: eutrophic (nutrient-rich) lake algal blooms July through September (ag runoff)

  46. Electron donor: H2O

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