Lec 12: Microbial Metabolism & Diversity (PDF)

PowerPoint® Lecture Presentations CHAPTER 3, 14, 15 Microbial Metabolism and Metabolic Diversity & Functional Diversity © 2018 Pearson Education, Inc. Microbial Cells Must Do Work • Cells must do work in order to survive and reproduce • Chemical work • Synthesis of complex molecules (i.e. anab...

PowerPoint® Lecture Presentations CHAPTER 3, 14, 15 Microbial Metabolism and Metabolic Diversity & Functional Diversity © 2018 Pearson Education, Inc. Microbial Cells Must Do Work • Cells must do work in order to survive and reproduce • Chemical work • Synthesis of complex molecules (i.e. anabolism) • Transport work • Take up of nutrients, elimination of wastes, and maintenance of ion balances • Mechanical work • Cell motility and movement of structures within cells • Work requires energy • Organisms obtain energy they need from an energy source present in their environment & convert it into a useful form • Most commonly used form of cellular energy = ATP • = Energy conservation Energy-Rich Compounds • Chemical energy released in redox reactions is primarily stored in certain phosphorylated compounds • ATP; the prime energy currency • Phosphoenolpyruvate • Free energy is released upon removal (hydrolysis) of the phosphate group • ATP is continuously hydrolyzed and resynthesized • For longer-term energy storage, microorganisms produce polymers that can be catabolized later to produce ATP • E.g. Glycogen, Poly-β-hydroxybutyrate, elemental sulfur Redox tower • Tendency to donate or accept electrons is expressed as reduction potential (E0’) Good electron donors Low reduction potential • Electrons will flow spontaneously from lower E0’ to higher E0’ (down the tower) • Greater the difference between donor & acceptor = greater ΔG Good electron acceptors High reduction potential Highest potential energy = best donors Energetically favourable transfer Lowest potential energy = best acceptors • So in terms of microbial metabolism ask yourself.. • Where are the electrons coming from? Organic or inorganic or through light activation? • Where are the electrons going? What is the terminal electron acceptor? Oxygen or some other compound? • Where is the carbon coming from? Organic or inorganic (CO2)? Energy classes of microorganisms • Chemotrophs: Conserve energy from chemicals • Organic chemicals = chemoorganotrophs • e.g. Oxidation of glucose • Inorganic compounds = chemolithotrophs • e.g. Oxidation of H2, H2S, NH3, Fe2+ Electron donors • Phototrophs: Conserve energy from light • Contain pigments that allows for the conversion of light energy into chemical energy • Oxygenic = Oxygen is produced Light energy absorbed • Cyanobacteria, algae • Anoxygenic = Does not yield oxygen • Purple and green bacteria, heliobacteria by pigment molecules converts weak electron donors into strong donors Catabolic diversity of prokaryotes Lets start with CHEMOORGANOTROPHS glucose Example of glucose as the electron donor glucose glucose H2O Chemolithotrophs • Use inorganic chemicals as electron donors for electron transport chain, instead of organic chemicals • Generates proton motive force for ATP synthesis • Carbon usually obtained from carbon dioxide (CO 2) • = autotrophs • But some can also use organic compounds mixotrophs • Carbon fixation usually occurs via the Calvin cycle • Requires ATP and NADH • Major groups of chemolithotrophs: • Hydrogen bacteria (donor = H2) • Sulfur bacteria (donor = H2S, S0, S2O32-, SO32-) • Iron bacteria (donor = Fe2+) • Nitrifying bacteria (donor = NH3, NO2-) Sulfur oxidizing bacteria Sulfur oxidizing bacteria Electrons liberated from this reaction used for energy S SO4- H2S + 2O2 SO4-2 + 2H+ + 8e- Sulfur-Oxidizing Bacteria Chemolithotroph Thermothrix, Thiobacillus and Beggiatoa • If it is a chemolithotroph it uses H2S and S0 as electron DONORS, and OXYGEN as the electron acceptor • Beggiatoa Filamentous, gliding bacteria • Found in habitats rich in H2S • Examples: sulfur springs, decaying seaweed beds, mud layers of lakes, sewage-polluted waters, and hydrothermal vents • Most grow mixotrophically • With reduced sulfur compounds as electron donors • And organic compounds as carbon sources Filamentous sulfur-oxidizing bacteria. Sulfur-Reducing Bacteria Chemolithotrophs or Chemoorganotroph • Key genera: Desulfovibrio, Desulfobacter • Over 30 genera of sulfate-reducers across five phyla of Bacteria and Archaea Most are Deltaproteobacteria • Some are Firmicutes • Some are Thermodesulfobacteria • Some are Nitrospira • Archaeoglobus in Archaea • Many are mixotrophs Dissimilative metabolism is the process by which an inorganic compound (NO 3 − , SO 4 2− , Fe3+, CO2) is reduced because it is used as an electron acceptor for anaerobic respiration Let’s go to Sulfur reducing bacteria.. They can be chemoorganotrophs because they use an organic electron donor…. H2S So sulfur reducing bacteria can be chemolithotrophs or chemoorganotrophs. use n ca o s Al They have in common that they reduce sulfur as the electron acceptor. H2S ! ! ! H 2 H2S Sulfur-Reducing Bacteria • Use SO42− and S0 as electron ACCEPTORS, and organic compounds (lactate or pyruvate) or H2 as electron donors • H2S is an end product • If they use H2 as electron donors then they are chemolithotrophs!!! • If they use organic compounds as electron donors then they are chemoorganotrophs!!! • Most are obligate anaerobes • Widespread in aquatic and terrestrial environments Hydrogen-Oxidizing Bacteria Chemolithotrophs • Key genera: Ralstonia, Paracoccus • Most can grow autotrophically with H2 as sole electron donor and O2 as electron acceptor ("knallgas" reaction) • Both gram-negative and gram-positive representatives Hydrogen oxidizing bacteria Figure 14.37 NOW, PHOTOTROPHS Phototrophs • Light is used instead of chemicals to drive electron transport & generate a proton motive force • Produces ATP (via ATPase) • = photophosphorylation • Most use CO2 as carbon source = photoautotrophs • If organic compound is used = heterotrophs • Two main groups of prokaryotic phototrophs: • Purple and green bacteria • Photosynthetic pigment = bacteriochlorophylls • Anoxygenic: Electrons derived from H2S or H2 • Cyanobacteria • Photosynthetic pigment = chlorophyll • Oxygenic: Electrons derived from H2O, producing O2 Prokaryotic phototrophs Purple and green bacteria Cyanobacteria Oxygenic Anoxygenic Reducing power ele ctr on s electrons Carbon Energy ADP Reducing power ele ctr on s Light ATP Carbon Energy ADP Light ATP Cyanobacteria Oxygenic Photoautotrophs • Key genera: Prochlorococcus,Crocosphaera, Synechococcus, Oscillatoria, Anabaena • Oxygenic phototrophs • Impressive morphological diversity (Figure 14.2) • Unicellular (divide by binary fission) • Unicellular (divide by multiple fission) • Filamentous (with heterocysts) • Filamentous (no heterocysts) • Branching filamentous Cyanobacteria • Most species are obligate phototrophs • Many cyanobacteria produce potent neurotoxins • Widely distributed in terrestrial, freshwater, and marine habitats • Can be phototrophic component of lichens • Often form extensive crusts in desert soils Unicellular Colonial Filamentous heterocystous Filamentous Filamentous branching Cyanobacteria: the five major morphological types of cyanobacteria. Heterocysts involved in nitrogen fixation not photosynthesis (loss of photopigments) Figure 14.8 Purple Sulfur Bacteria Anoxygenic Photoautotrophs • Key genera: Chromatium, Ectothiorhodospira • Found in illuminated anoxic zones of lakes and other aquatic habitats where H2S accumulates, as well as sulfur springs • Use hydrogen sulfide (H2S) as an electron donor for CO2 reduction in photosynthesis • Sulfide oxidized to elemental sulfur (S0), which is stored as globules either inside or outside cells Sulfur later disappears as it is oxidized to sulfate (SO42−) THIS IS ANOXYGENIC PHOTOTROPHY Figure 14.9 Figure 14.10 THIS IS PHOTOHETEROTROPHY Uses light for energy BUT uses an organic compound for carbon building blocks. Also can use H2S instead of water!! H2 All four possible combinations of obtaining carbon and ATP exist in microbes. First prefix is energy, second is carbon. (Chemoautotroph = Chemolithotroph) Winogradsky Column Microbial diversity, metabolic diversity and microbial ecology go hand in hand. The compounds that are reduced are ultimately oxidized by other microbes. Microorganisms play key roles in the cycling of carbon, sulfur, nitrogen and iron.