Why are anaerobic organisms simple and aerobic organisms complex?

Andreas Brune Andreas.Brune at uni-konstanz.de
Wed Nov 29 06:00:06 EST 1995


In article 
<Pine.D-G.3.90.951128091037.24843A-100000 at necc.mass.edu>,
   mkolotila at NECCADM1.NECC.MASS.EDU (Michael Kolotila x3887) 
wrote:
..
>Also, since anaerobic bacteria do not use oxygen as their 
>terminal electron acceptor, the can use other substances and if 
my 
>understanding is correct generate as much energy as aerobe.  One 
>Clostridium, an anaerobe, has a generation time under ideal 
conditions of 
>8 minutes.  I find it hard to believe that it can derive enough 
energy 
>from glycolysis or fermentation to support that type of growth 
rate.

Michael, it is an often encountered misconception that the 
energetics of an organisms metabolism correlates with its 
generation time. If you look through the microbial world you find
both aerobes growing extremely slowly as well as 
fermenting anaerobes growing much faster than most aerobes.

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). 

So were back to the point raised earlier in this thread that 
anaerobes are severely energy-limited when compared to aerobes, 
and presumably this precludes any elaborate multicellular 
architecture calling for, e.g., expensive exchanges of 
metabolites by intra- and extracellular circulation systems. But 
this is pure speculation.

Regards,

Andreas


Dr. Andreas Brune * Mikrobielle Oekologie * Fakult. f. Biologie * Universitaet Konstanz * Postfach 5560, M654 * 78434 Konstanz * Germany * Phone: +49-7531-883282 * Fax: +49-7531-882966

~!



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