Why are anaerobic organisms simple and aerobic organisms complex?

Peter Herman herman at populus.slu.se
Tue Dec 5 09:41:08 EST 1995


: Your conclusion (probably derived from this wrong assumption)  
: that a clostridial metabolism must yield as much energy in 
: fermentation as an aerobic organism would in oxidizing a given 
: substrate is much easier to prove wrong: Any microbiology 
: textbook will tell you that the ATP yield in the fermentative 
: degradation of, e.g. glucose, yields 2-4 ATP (depending on the 
: type of fermentation involved), while a respiratory degradation 
: will yield 26-38 ATP per glucose. The reason for this difference 
: is not only a mechanistical one (pathway) but mostly based on the 
: much smaller free energy changes in the respective fermentative 
: reactions (thermodynamics). 

: Andreas

Even where the anareobic metabolism is respiratory with alternate 
terminal electron acceptors such as NO3 or SO4, the ATP yield
is lower than with O2 because their half reactions coupled with the 
NADH <--> NAD +e- + H+ half reaction yield less energy.

You can easily show how dependent growth rate is on the nature of the
substrate by growing something like E. coli aerobically on Glucose/mineral
salts and a rich medium and comparing the rates and C-use.  The growth is
faster and the C-use is less/cell built when the cell can transport most
of its building blocks pre-formed rather than having to build them ll from
scratch. 

Peter
--
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R. Peter Herman				email	Peter.Herman at mv.slu.se
Sveriges Lantbruksuniversitet		Phone:	+46 18 67 12 20
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