Dear Jim
The problem here is that the energy yield from anaerobic respiration with
nitrate is NOT as high as from aerobic respiration. Anaerobic respiration
utilizes an electron-transport chain in the bacterial cytoplasmic membrane.
This is thus electron-transport-linked phosphorylation (ETP) but while
aerobes employ oxygen as the terminal electron acceptor, anaerobes can
utilize sulphate, formate, nitrate, nitrite or CO2. The process depends on
the electrochemical potential between redox partners of different redox
potential, which is used to drive the production of ATP (Thauer et al,
1977). The free-energy change associated with ETP in anaerobes is much less
than that achieved when oxygen can be utilized, due to the high affinity of
oxygen for electrons. This may be one reason why anaerobes relying mainly on
anaerobic respiration for energy production tend to grow more slowly than
aerobes.
The 'Thauer' reference is quite old but absolutely essential reading,
especially if you are not a microbiologist. The full citation is:
Thauer R K, Jungerman K and Decker K (1977) Energy conservation in
chemotrophic anaerobic bacteria.
Bacteriological reviews, Vol 41 Pages 100 - 180
This will answer your question (and more) better than I can!
Best wishes,
Andrew Pridmore
