23 - PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 23...

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PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 23 The Methanogens
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Alessandro Volta (1745-1827) The discovery of “combustible air” • Methane was discovered by the Italian physicist Alessandro Volta in 1776. He collected gas from marsh sediment and showed that it was flammable. • Known best for the development of the first electric cell in 1800. The electric unit, the volt, is named in his honor. • The Volta experiment can easily be reproduced if methane trapped in freshwater sediments is collected in a large, stoppered funnel and ignited. • Below is a 225-year old combustion chamber designed by Volta. It contains 2 ports connected to gold foil that produce an electric spark within the chamber. • “The air of swamps…ignites and explodes most loudly, if to one part of it, we add 8 or 10 parts of ordinary air” Wolfe (2004) ASM News 70:15-18
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Why do anaerobes discard so much chemically entrapped energy? Wolfe (2004) ASM News 70:15-18 • Anaerobic oxidation-reduction reactions are favorable only under particular conditions. • Fermentative anaerobes carry out only limited oxidations, passing electrons to a more oxidized fraction of the original substrate molecule or to protons (forming H 2 ). • The main end products of fermentation are acetate, propionate, butyrate, and hydrogen. •H 2 is produced in the fermentation of butyrate and propionate, but its accumulation thermodynamically limits this process. This process is dependant on a sink for the H 2 . • Methanogens utilize H 2 and reduce CO 2 to methane. Methane is also produced from acetate and a number of other substrates. • Comparing the energy produced from the partial oxidation of glucose (eq. 1) with that to the complete aerobic oxidation of glucose (eq. 3) indicates that 85% of the energy from glucose remains in methane.
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www.greenhouse.nsw.gov.au Many chemical compounds found in the Earth’s atmosphere act as “greenhouse gases.” These gases allow sunlight to enter the atmosphere freely. When sunlight strikes the Earth’s surface, some of it is reflected back towards space as infrared
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23 - PROKARYOTIC DIVERSITY BIOL 4125 SPRING 2009 LECTURE 23...

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