Chapter 3. Energetics Respiration Growth. Types of energy metabolism. Chemoheterotrophs Energy source (electron donor):organic carbon Carbon source: organic carbon. An electron donor is an energy source An electron acceptor is a respiratory substrate. Chemoheterotrophs. Electron donor.
An electron donor is an energy source
An electron acceptor is a respiratory substrate
NO3, Fe(III), Mn(IV), SO4, CO2anaerobic respiration
NH4+, Fe(II), Mn(II), HS-
NO3, Fe(III), Mn(IV), SO4, CO2anaerobic
N2O, Fe(II), Mn(II), H2S, CH4
Carbon source, electron acceptor
Inorganic C (CO2)
Terminal electron acceptor
in Photo System 1
In a chemical reaction, only part of the energy is used to do work. Energy available for work is called “free energy” or DG.
The rest of the energy is lost to entrophy.
DG = -RT log Keq where Keq = [C] [D] / [A] [B] from rxn:
A + B C + D
If logKeq is a negative value, this means the reaction can only proceed if energy is added (endothermic rxn).
When logKeq is a negative value, DG is positive.
If logKeq is a positive value, this means the reaction is favored and, in fact, gives off energy (exothermic rxn).
When logKeq is a positive value, DG is negative.
Terminal electron acceptor
Which ones are exothermic and which ones are endothermic?
oxidation state (volts)
(CH2O CO2) electron donor
Electron ReductionElectron Reduction Difference
AcceptorPotential (V) Donor Potential (V)(V)
O2 H2O+0.81 CH2O CO2 -0.47 -1.28
NO3 N2 +0.75 CH2O CO2 -0.47 -1.22
SO4 H2S -0.22 CH2O CO2 -0.47 -0.25
The sign and magnitude of the difference represents how much
free energy is available to the cell to do work.
= #cells produced/unit time (growth rate)
t2 – t1
More closely mimics natural systems
Engineered wastewater treatment system operates like a chemostat
S=limiting nutrient conc.
D=dilution (flow) rate
Energy source (electron donor)
(Terminal electron acceptor)
Processes occurring in a chemostat
m = D
1 mol of glucose is equivalent to 180g
cell mass produced from 1 mol glucose = 180g x 0.4 = 72g
cell mass is expressed as C5H7NO2 (mol. wt. = 113g/mol)
moles of cell mass produced from 1 mol of glucose
72g cell mass/113 g/mol cell mass = 0.64 mol cell mass
In terms of carbon:
for cell mass,
(0.64 mol cell mass)(5 mol C/mol cell mass)(12 g/mol C) = 38.4g C
for substrate (glucose),
(1 mol substrate)(6 mol C/mol glucose)(12 g/mol C) = 72 g C
% of glucose carbon found in cell mass is (38.4 g C/72 g/C)x100 =53%
by difference 47% glucose carbon is released as CO2
% substrate consumed
that ends up in cell mass
Developing genetically-engineered microbes and plants to carry out specific remediation activities when indigenous organisms can’t do the job