lec 15 - Lecture 15 Biogeochemical Cycles on Earth Today's...

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Biogeochemical Cycles on Earth Today’s topics : Cycles of carbon, nitrogen, sulfur, phosphorus, iron, etc. Autotrophic carbon fixation and organic recycling to CO 2 Nitrogen fixation & recycling Sulfur oxidation and reduction Assimilation vs dissimilation Lecture 15 (see pages in chapter 8) (also see chapters 10, 24)
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Most carbon is inorganic in the form of rocks & sediment ( 99.5%) . The rest (0.5%) is CO 2 in the oceans, atmosphere, or in inorganic carbon derived from living cells. Only a small fraction (0.003%) is organic in the form of either living or decaying materials * . *not counting hydrocarbons (coal, oil, natural gas) Carbon on Earth
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Carbon is continually “Fixed” and Recycled Microbes are essential in: • recycling organic carbon to CO 2 Microbes play a critical role in : • Carbon fixation by photosynthesis • Carbon fixation by chemosynthesis
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Nutritional classes of microorganisms • Chemotroph chemo- = “chemical” troph = “feeding” • Phototroph photo- = “light” troph = • Autotroph auto- = “self” troph • Heterotroph hetero- = “different” troph Source of Energy for Life Source of Carbon for Life Uses CO 2 Uses organic carbon Uses chemicals Uses photons
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Autotrophic fixation of Organic Carbon Numerous microbial pathways! Calvin cycle Reductive TCA cycle Hydroxy-propionate pathway Reductive acetyl-CoA pathway Glycine-serine pathway • Ribulose monophosphate pathway (plants, cyanobacteria) (green sulfur bacteria, sulfate reducing bacteria) ( Chloroflexus species) (many anaerobic autotrophs, methanogens) (many C-1 oxidizing bacteria) (many C-1 oxidizing bacteria)
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The “fixed” Organic Carbon is Present as - geological carbon * (coal, gas, oil & methane hydrates) - man-made compounds (plastics, pesticides, herbicides, drugs, and other synthetic compounds) - complex biomolecules (polymers such as protein, DNA, carbohydrate) -small biomolecules (substrates, intermediates & cell waste) Living and Dead organisms in the form of:
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…some microbe has evolved a way to degrade it! a) as a source of cell energy, or b) as a source of cell carbon An excellent generalization… For every naturally occurring organic compound...
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Consider microbes growing on soil particles
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Microbes form micro-colonies on soil particles Very high populations! (10 6 to 10 8 cells/gram) Can: • Respire? • Ferment?
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If by respiration: (RLP and sometimes SLP) If by fermentation: (SLP only) Use an oxidized compound as electron acceptor! Organic compounds serve as electron donors The General Plan (DH + A D + AH) Options? (if oxygen present) Use NADH, FAD, & succinate as electron donors to O 2 .
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Pyruvate oxidation & TCA cycle pathway yield 2 NADPH 4 NADH 2 FADH 2 GTP Per two Ac-CoA 4 CO 2 (GTP formation is by SLP) TCA cycle Per two C3 2 Ac-CoA + 2 CO 2 2 NADH
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Formation of the proton motive force
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