1.018/7.30J Fall 2009 Ecology I: The Earth System READINGS: Textbook p. 43, 84 – 88; 673-674  Luria. 1975. Overview of photosynthesis.  Kaiser, J. 1995. Can deep bacteria live on nothing but rocks and water? Science. 270:377.  Jannasch, H. Life at the sea floor. Nature. 1995 374:676-677  Lovley, D. Bug juice harvesting electricity with microorganisms. 2006. Nat Rev. Microbiol. 4:497  Jetten, M et al. Microbiology & application of the anaerobic ammonium oxidation (‘anammox’) process Curr Opin Biotechnol. 2001 Jun; 12(3):283-8. Lecture 3: How to be Alive Carbon and energy transformations Nature has put itself the problem of how to catch in flight light streaming to earth and to store the most elusive of all powers in rigid form.” Mayer, 1842, discovered law of conservation of energy Summary energy inputs: solar chemical Carbon Metabolism O2 and CH2O Heterotrophs “self-Autotrophs “nourished from nourishers ” others ” CO2 and H2O Organisms can be broadly classified by how they obtain their energy and carbon Living organisms can be generally categorized by their primary sources of carbon, reducing power (electrons), and energy. Typically whether these carbon, energy and electron sources are organic, or inorganic, guides the classification. The different types of metabolisms found in these diverse organisms, that differentially oxidize or reduce different organic and inorganicchemicals in the environment, is what drives biogeochemical cycles in the biosphere. Their integrated activities balance oxidation and reduction reactions in the environment, and keep the system cycling between the oxidized and reduced forms of organic and inorganic materials. A. Autotrophs These “self-nourishers” typically get their energy from the sun (photoautotrophs), or from reduced inorganic compounds (chemoautotrophs a.k.a. chemolithotrophs). They get their carbon for growth and production of new cells from CO2. The energy generating reactions produces ATP’ and NADPH’’, which provide stored biochemical energy and reducing power forbiosynthesis and production of new cells. For oxygen-generating photosynthetic organisms (like plants and cyanobacteria), the light-requiring reaction that generates energy is known as the Hill, or “light reaction”. There are a number of different ways that organism can incorporate, or “fix” inorganic CO2 into organic material. In plants, the Calvin Cycle, is common biochemical pathway, and uses the stored energy and reducing power (ATP and NADPH) to convert CO2 to CH2O (sugar). 1. Oxygenic Photosynthesis (produces O2) Who? Plants, cyanobacteria, eukaryotic algae C Source? CO2 Energy Source? Sunlight Electron Donor? H2O (the oxygen from the water used in photosynthesis, is what produces the O2 we breath !) Where? In aerobic, light conditions CO2 + H2O + hν  CH2O + O2 2. Anoxygenic Photosynthesis (doesn’t produce O2) Who? Bacteria (e.g. Purple sulfur bacteria, green sulfur bacteria) C Source? CO2 Energy Source? Sunlight Electron Donor? H2S, H2, Fe2+ Where? In anaerobic, light conditions CO2 +2 H2S + hν  CH2O + 2 S + H2O 3. Chemosynthesis Who? Chemoautotrophic bacteria, aka chemolithoautotrophs (“rock eaters”) C Source? CO2 Energy Source? Reduced inorganic compounds (CH4, H2, NH4, H2S, Fe2+) Electron Donor? Reduced inorganic compounds Where? In microaerobic or anaerobic, dark conditions Sulfur oxidizing bacteria: H2S  S  SO42- Methanotrophs: CH4 (methane)  CO2 Nitrifying bacteria: NH4+  NO2- NO3- Iron oxidizing bacteria: Fe2+  Fe3+ *ATP = adenosine triphosphate. (ADP = adenosine DI phosphate) 2**NADPH = nicotinamide adenine dinucleotide phosphate B. Heterotrophs These organisms (“nourished by others”) get their energy and carbon by oxidizing (“burning”) reduced organic compounds, eg organic matter. ATP and NADH*** are produced, which can then be used elsfor biosynthesis, growth and the production of new cells. (***NADH = nicotinamide adenine dinucleotide (chemically similar to NADPH, NADH is oxidized to facilitate ATP production, while NADPH is associated with biosynthesis). 1. Aerobic respiration Who? Aerobic eukaryotes and prokaryotes C Source? CH2O (sugars, amino acids, organic acids, other organic compounds) Energy Source? CH2O Electron Acceptor? O2 Where? Aerobic conditions These reaction is essentially the reverse of the Calvin cycle. O2 is the final electron acceptor. Plants also carry out this reaction to get energy for their growth and metabolic processes. CH2O + O2  CO2 + H2O 2. Fermentation Who? Eukaryotes and prokaryotes C Source? CH2O Energy Source? CH2O Electron Acceptor? organic compounds (part of the energy source gets oxidized, the other part reduced) Where? Anaerobic conditions This is only the first part of respiration and results in partial breakdown of glucose. The products are organic acids or alcohols (e.g., lactic acid, ethanol, acetic acid) rather than CO2. 3. Anaerobic respiration Who? Prokaryotes only C Source? CH2O Energy Source? CH2O Electron Acceptor? Oxidized inorganic compounds (SO42-, Fe3+, NO3+, etc.) Where? Anaerobic conditions Very similar to aerobic respiration, except that O2 is not the final electron acceptor. Instead, another oxidized compound such as SO42-, NO3-, or CO2 is the final electron acceptor. Iron reducing bacteria: Fe3+  Fe2+ Denitrifying bacteria: NO3- NO2- NO2- N2 Sulfate reducing bacteria: SO42- S  H2S Methanogens: CO2  CH4(methane) 3Overview of Life on Earth The energy that drives all life processes is organized around oxidation/reduction reactions. Ultimately on Earth today, oxygenic photosynthesis, and energy from the sun, fuels the entire biosphere. Oxygenic photosynthesis produces (by the splitting of water as a reducing agent) one of the most powerful oxidants known – oxygen. The biosphere on the contemporary Earth runs largely on the carbon produced by CO2 fixation by oxygenic photosynthesis, and on the free energy difference between O2 and organic carbon, which heterotrophs use to fuel their metabolism. The autotrophs synthesize glucose using solar or chemical energy, which is broken down through respiration (either their own or that of the organisms that eat them) to provide the energy necessary for “biological work”. Redox reactions are central to all of