09 biogeochemical cycles.ppt

09 biogeochemical cycles.ppt - CEE 266 ENVIRONMENTAL...

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Unformatted text preview: CEE 266 ENVIRONMENTAL BIOTECHNOLOGY Lecture 9 (Microbe-mediated Global Biogeochemical Cycles) The Carbon Cycle Figure 24.1 Major Carbon Reservoirs on Earth The Carbon Cycle   CO2 in the atmosphere is the most rapidly transferred carbon reservoir   Phototrophs are the foundation of the carbon cycle   Oxygenic phototrophic organisms can be divided into two groups: plants and microorganisms   Plants dominant phototrophic organisms of terrestrial environments   Phototrophic microbes dominate aquatic environments Redox Cycle for Carbon Figure 24.2 Syntrophy and Methanogenesis   Methanogenesis is central to carbon cycling in anoxic environments   Most methanogens reduce CO2 to CH4 with H2 as an electron donor; some can reduce other substrates to CH4 (e.g., acetate)   On a global basis, biotic processes release more CH4 than abiotic processes   Methanotrophy significantly reduces the release of CH4 into the atmosphere Anoxic Decomposition Figure 24.3 Estimates of CH4 Released into the Atmosphere The Nitrogen Cycle   Nitrogen fixation: conversion of N2 to ammonia   Assimilation: conversion of NH3 to organic-N (not redox)   Nitrification: oxidation of ammonia to nitrate   carried out in 2 steps: nitrosification and nitrification   Denitrification: reduction of nitrate to gaseous nitrogen products and is the primary mechanism by which N2 is produced biologically   Anammox: anaerobic oxidation of ammonia to N2 gas Redox Cycle for Nitrogen Figure 24.5 Redox Reactions in Nitrogen Cycling Process Reaction Nitrification NH3 NO2- NO3- Denitrification Organic compound Organic compound Nitrogen fixation Anammox Electron Donor NH3 + NO2- N2 Electron Acceptor The Sulfur Cycle   Sulfur transformations by microbes are complex   The bulk of sulfur on Earth is in sediments and rocks as sulfate and sulfide minerals (e.g., gypsum, pyrite)   The oceans represent the most significant reservoir of sulfur (as sulfate) in the biosphere Redox Cycle for Sulfur Figure 24.6 The Sulfur Cycle   Hydrogen sulfide is a major volatile sulfur gas that is produced by bacteria via sulfate reduction or emitted from geochemical sources   Sulfide is toxic to many plants and animals and reacts with numerous metals   Sulfur-oxidizing chemolithotrophs can oxidize sulfide and elemental sulfur at oxic/anoxic interfaces The Sulfur Cycle   Organic sulfur compounds can also be metabolized by microbes   The most abundant organic sulfur compound in nature is dimethyl sulfide (DMS)   DMS can be transformed via a number of microbial processes The Phosphorus Cycle   Phosphorus is biologically important   Nucleic acids   ATP, ADP, AMP, NAD(P)H   Phospholipids   There is no significant component in global P cycle   Phosphorus conversions are not microbially mediated   P is cycled through plants, animals, fossils, and rocks   Long turnover times Redox Cycle of Iron Figure 24.7 Oxidation of Ferrous Iron (Fe2+) Figure 24.8a Figure 24.8b Role of Iron-Oxidizing Bacteria in Oxidation of Pyrite Pyrite (FeS2) • One of the most common forms of iron in nature • Its oxidation by bacteria can result in acidic conditions in coal-mining operations Figure 24.10a Pyrite and Coal Figure 24.9 Role of Iron-Oxidizing Bacteria in Oxidation of Pyrite Figure 24.10b The Iron Cycle  Acid Mine Drainage   An environmental problem in coal-mining regions   Occurs when acidic mine waters are mixed with natural waters in rivers and lakes   Bacterial oxidation of sulfide minerals is a major factor in its formation Acid Mine Drainage from a Bituminous Coal Region Figure 24.11 Microbial Leaching of Ores  Microbial Leaching   The removal of valuable metals, such as copper, from sulfide ores by microbial activities   Particularly useful for copper ores   Microbes are also used in the leaching of uranium and gold ores Effect of the Acidithiobacillus ferrooxidans on Covellite Figure 24.13 Microbial Leaching of Ores   In microbial leaching, low-grade ore is dumped in a large pile (the leach dump) and sulfuric acid is added to maintain a low pH   The liquid emerging from the bottom of the pile is enriched in dissolved metals and is transported to a precipitation plant   Bacterial oxidation of Fe2+ is critical in microbial leaching as Fe3+ itself can oxidize metals in the ores The Microbial Leaching of Low-Grade Copper Ores A Typical Leaching Dump Effluent from a Copper Leaching Dump Figure 24.14a The Microbial Leaching of Low-Grade Copper Ores Recovery of Copper as a Metallic Copper Figure 24.14c The Microbial Leaching of Low-Grade Copper Ores Small Pile of Metallic Copper Removed from the Flume Figure 24.14d Arrangement of a Leaching Pile and Reactions Figure 24.15 Cycling of Trace Elements   Present in low concentrations in soils, water, and biota   Cu, Co, Ni, Zn, Mo, Mn – important for cell functions   Pb, Hg, As, Cd, Se, Cd, Cr – toxic   Oxidation state is important, e.g., Cr6+ toxic but Cr3+ is not   Microorganisms can mobilize, accumulate, precipitate or detoxify trace metals,   Implications for mining and remediation   Heavy metal resistance Mercury and Heavy Metal Transformations   Mercury is of environmental importance because of its tendency to concentrate in living tissues and its high toxicity   The major form of mercury in the atmosphere is elemental mercury (Hgo) which is volatile and oxidized to mercuric ion (Hg2+) photochemically   Most mercury enters aquatic environments as Hg2+ Biogeochemical Cycling of Mercury Figure 24.17 Mercury and Heavy Metal Transformations   Hg2+ readily absorbs to particulate matter where it can be metabolized by microbes   Microbes form methylmercury (CH3Hg+), an extremely soluble and toxic compound   Several bacteria can also transform toxic mercury to nontoxic forms   Bacterial resistance to heavy metal toxicity is often linked to specific plasmids that encode enzymes capable of detoxifying or pumping out the metals Mechanism of Hg2+ Reduction to Hgo in P. aeruginosa The mer operon Figure 24.18a Mechanism of Hg2+ Reduction to Hgo in P. aeruginosa Transport and Reduction of Hg2+ Figure 24.18b Arsenic in the Environment   Natural Sources   Inorganic As: associated with S, Fe, Cu, Se, Te, Ni, Co in pyrites.   Organic As: methylated arsenic acids   Anthropogenic Sources   Coal combustion, mine tailings, pesticides, wood preservatives, solar cells, catalysts Species of Interest   Arsenate (As(V))   H2AsO4-, HAsO42  Arsenite (As(III))   H3AsO3, H2AsO3  As (III) more toxic than As (V)   Substitutes P during ATP formation through arsenolysis @ substrate & mitochondrial levels   Reacts with enzymatic functional groups, decreases ATP formation Dissimilatory Arsenate-Reducing Prokaryotes   Anaerobic bacteria   Arsenate as e- acceptor   Organic matter is e- donor   The arsenate reductases (ArrAB) are located in the periplasm   ArrAB are encoded by arrA and ArrB genes Arsenite Oxidases ...
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This note was uploaded on 02/02/2012 for the course CEE 266 taught by Professor Shailymahendra during the Fall '11 term at UCLA.

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