Presentation on theme: "Fermentation: Catabolism of carbon in the absence of a terminal electron acceptor (like O2) for electron transport chain."— Presentation transcript:
1Fermentation:Catabolism of carbon in the absence of a terminal electron acceptor (like O2) for electron transport chain
2Compare the DEh for putting electrons onto O2 vs. lactate Figure: 05-09Caption:The electron tower. Redox couples are arranged from the strongest reductants (negative reduction potential) at the top to the strongest oxidants (positive reduction potentials) at the bottom. As electrons are donated from the top of the tower, they can be “caught” by acceptors at various levels. The farther the electrons fall before they are caught, the greater the difference in reduction potential between electron donor and electron acceptor and the more energy that is released. As an example of this, on the left is shown the differences in energy released when a single electron donor, H2, reacts with any of three different electron acceptors, fumarate, nitrate, and oxygen.
3The unusual fermentation of oxalate by Oxalobacter formigenes Figure: 17-52aCaption:The unique fermentations of succinate and oxalate. (a) Succinate fermentation by Propionigenium modestum. A sodium-translocating ATPase produces ATP; sodium export is linked to the energy released by succinate decarboxylation.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?
5Photosynthesis and Autotrophy I. PhotosynthesisA. General AspectsB. Classes of Photosynthetic BacteriaC. Mechanism of Photosynthesis1. Anoxygenic Photosynthesis2. Oxygenic PhotosynthesisD. Halobacterium (light-driven H+ pump)II. AutotrophyB. Types of Autotrophic Pathways
7PHOTOSYNTHESIS (Photoautotrophy) Excited stateXphotonCO2NADP+e-CH2ONADPHGround state
8PHOTOAUTOTROPHY: 2 reactions 1. LIGHT CHEMICAL ENERGY(ATP)2. CO2 reduction → Organic compounds
9Phototrophic Prokaryotes: the metabolic menu Group Reducing power Oxidized productPurple nonsulfur bacteria H2, reduced organic Oxidized organicsPurple sulfur bacteria H2S SO4-2Green sulfur bacteria H2S SO4-2Green non sulfur bacteria* H2S SO4-2Heliobacteria** Lactate, organics Oxidized organicsCyanobacteria H2O O2Prochlorophytes*** H2O O2*Most ancient?**Gram positive, heterotrophs***Related to cyanobacteria
10Three 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)
11Carotenoid-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 transferNagel et al Mechanics of Biolenergetic Membrane Proteins 33: 863
12Photosystems do not absorb at short enough wavelengths to split water, so must get e-’s somewhere else.Cyclic: electrons run in closed circuit
13Photosystems can take light energy strong enough to split water. Non-cyclic (although cyclic can occur)
14Chlorophyll: 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 anoxicNot enough energy to extract e- from H2O; must use H2S insteadEventually, chlorophyll evolved. Utilizes a short enough wavelength (680 nm) to split H2O and generate O2.
15Consequence 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- H2O OH ·At first, protected by Fe+2 (ferrous iron): Fe+2 + O2 FeOH3Banded iron formations from Wittenoom Gorge in Australia
16Consequence of oxyenic photosynthesis in evolution: Bacteria began evolving carotenoids: protection against singlet oxygen; convert to less toxic stateEventually (at least 2 billion years ago), used up ferrous ironAccumulation of O2 in atmosphereO2 + 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
17Production 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.
18Cellular 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.
19Detection of algal blooms from satellites via remote sensing: relies on reflected spectral properties of chlorophylls.Nutrient upwelling (El Nino) = phytoplankton blooms
20Photosynthesis 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 climateMany marine microbes use light to drive ATP synthesis.Photic zone = upper 300 metersOxygenic and anoxygenic photosynthesisChlorophylls a and b (cyanobacteria and relatives; algae)Proteorhodopsin (very similar to bacteriorhodopsin but Bacteria, not Archaea)
30Photosynthetic Membranes Reaction center chlorophyll-few-convert light energy to ATPLight harvesting chlorophyll-many- “antenna”-captures “faint signal” of low light environmentsAccessory pigmentsCarotenoidsPhycobilins
31… light harvesting complex in cyanobacteria, plants
33Purple Bacteria (within phylum Proteobacteria) photosynthetic membranes are lamellae or tubes with the plasma membranebacteriochlorophyll a or baccessory pigments are purple colored carotenoid pigments(see Fig in your text)may live as photoheterotrophstwo types: 1. sulfur2. nonsulfur
34Green Bacteriaphotosynthetic membranes are vesicles attached to but not continuous with the plasma membranebacteriochlorophyll c, b, or e (small amount of a in LH and RC)accessory pigments are yellow to brown-colored carotenoidstwo types: 1. sulfur (green sulfur bacteria phylum)2. nonsulfur (green nonsulfur bacteria phylum)
35Heliobacteriaplasma membrane only (no specialized photosynthetic membranes)bacteriochlorophyll gPhotoheterotrophs: require organic carbonThese are the only Gram-positive photosynthetic bacteria
41Variation on the Theme * * ATP & NAD(P)H ATP only ATP only * Off to supply reducing power for CO2 fixation via reverse citric acid cycle
42Green Sulfur Bacteria (Chorobium, Chlorobaculum, Prosthecochloris) Aquatic, anoxic environmentsMost are facultative heterotrophs; strict autotrophy requires reverse TCA cycleHave chlorosomes: very efficient at light harvesting so live at great depthsMay 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)
43Green Non Sulfur Bacteria (Choroflexus)Filamentous, form microbial mats with cyanobacteria in neutral to alkaline hot springsLike Green Sulfur Bacteria: has chlorosomesBut reaction center of in cell membrane is like purple bacteriaEarliest known photosynthetic bacterium: perhaps reaction center first, chlorosome later by HGTMost are facultative heterotrophs; CO2 fixation requires hydroxypropionate pathway (unique to very ancient organisms)
44Light harvesting complex in green photosynthetic bacteria (both sulfur and non-sulfur) Chlorosome is a giant antenna: Bchl c, d, or eBP = baseplate (proteins)LH = light harvesting complex (Bchl a)RC = reaction center (Bchl a)
45Chlorosomes (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.
46Mechanism of Photosynthesis Oxygenic Photosynthesis Photosystems I & IINoncyclicYour text, FigCyanobacteriaAlgae (protists)Plants
47Cyanobacteria (phylum contains cyanobacteria and prochlorophytes) Synechococcus, Oscillatoria, Nostoc, Anabaenaphotosynthetic mebranes are multilayered lamellaeformerly called “blue-green algae” but now known to be prokaryotic and possess peptidoglycanchlorophyll a onlyaccessory pigments are carotenoids and phycobilin proteinsPhotosystem I and II are present (oxygenic photosynthesis)AutotrophsGas vesicles frequentSome are filamentous, N2 fixing (heterocysts)
48Lake Mendota up close: eutrophic (nutrient-rich) lake algal blooms July through September (ag runoff)
52Halobacterium-typeUse light-driven proton pump consisting of patches of the pigment bacteriorhodopsin in cytoplasmic membranebacteriorhodopsin resembles rhodopsin, the visual pigmentAbsorbs light near 570 nm (green region of spectrum)Extreme halophile (2-4M NaCl = 12-23%): balances Na+ outside with K+ inside to maintain osmotic equilibriumHeterotrophs (use amino acids and organic acids for growth)Most are obligate aerobes; some can do anaerobic respiration or fermentation
53Solar SaltEvaporationPonds (salterns) in CARed colorationdue to carotenoids ofhalobacteria
54Colonies of halobacteria isolated from Portsmouth salt piles. Plates contain 25 % NaCl !
55Oops, wrong, outdated hypothesis HalobacteriaOops, wrong, outdated hypothesisDomain ArchaeaNot autotrophs - grow as chemoheterotrophs but can function as phototrophsBacteriorhodopsin, proteorhodopsin = cytoplasmic membrane-associated photopigment similar to rhodopsinof mammalian eye.Bacteriorhodopsin is a light driven ion (proton) pump...Homologous protein in Halobacteria is called halorhodopsin; a chloride pump
56Correct; see next slide Light at 570 nm excites the retinal chromophore of bacteriorhodopsin, converting it from its normal all-trans conformation to a cis form. Conversion instigates the movement of a proton across the membrane. Proton loss returns retinal to its all-trans form.Correct; see next slideChloride ions flow across membrane in reverse direction for halorhodopsinLight + H+ = cisLoss of H+ = trans
57Arrangement of bacteriorhodopsin in the cytoplasmic membrane: Purple structures are proteins (opsin) that hold the chromophore (retinal)
58Current model for how bacteriorhodopsin and halorhodopsin work… Biochemical studies show that rather than transporting H+ out, bacteriorhodopsin (BR) may actually transport OH- in and halorhodopsin (HR) may transport in a Cl- (from all that NaCl in its environment)Bacteriorhodopsin in the cell membrane. CP = cytoplasm, EC = extracellular space. Arrows indicate direction of ion transfer.Bacteriorhodopsin and its retinal chromophore. Yellow arrow indicates direction of ion transfer.
59Autotrophy General Aspects Heterotrophs: organisms requiring organic compounds as a carbon sourceAutotrophs: organism capable of biosynthesizing all cellular material from CO2; CO2 as a sole carbon source