[Plant-education] cyclic electron transport in bacterial photosynthesis

Catharina Coenen via plant-ed%40net.bio.net (by ccoenen from allegheny.edu)
Tue Mar 4 19:27:09 EST 2008


Can someone please help me understand the following statement from 
Raven et al. Biology 8th edition (p. 153) on cyclic 
photophosporylation in sulfur bacteria:

"The hydrogen atoms extracted from H2S are used as a source of 
protons for driving ATP pumps and are not available to join carbon. 
Bacteria that are restricted to this process therefore must scavenge 
hydrogens from other sources, an inefficient undertaking."

My old edition of Gottschalk Bacterial Metabolism states that 
"reduced sulfur compounds are preferentially used as H-donors by 
[phototrophic bacteria]" for CO2 reduction.

And Brock's Microbiology, (2006, p. 542) states that "Reducing power 
(NADH) [....] for purple sulfur bacteria [...] usually comes from H2S [...]."

Am I misreading Raven et al. somehow, or is their explanation in 
contradiction to the Microbiology textbooks?

Thanks for any clarification you can provide,

Catharina


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Dr. Catharina Coenen
Associate Professor of Biology

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