1. 3.13 Catabolic Diversity Chemolithotrophy
Uses inorganic chemicals as electron donors
Examples include hydrogen sulfide (H2S), hydrogen gas (H2), ferrous iron (Fe2+), ammonia (NH3)
Begins with oxidation of inorganic electron donor
Uses an electron transport chain and transmembrane ion gradient

2. Dissimilative Iron Oxidizers are chemolithotrophs (13.9 and 14.15)
Oxidize Fe2+ to Fe3+
Very widely distributed in many environments where Fe2+ is available
Autotrophic or heterotrophic
Aerobic or anaerobic
Archaea or Bacteria

3. Acidithiobacillus ferrooxidans is a representative iron oxidizer
Acidophile at pH 2-3
Acid environments with Fe2+
Fe2+ -> Fe3+ -> FeOH3

4. Figure 13.24 (pH 2) (pH 6) + ATP ATP e– e– Out Outer membrane cyt c
Electron transport generates proton motive force.
Rusticyanin e–
Periplasm
Reverse e– flow e–
NAD+ Q
cyt bc1
cyt c
cyt aa3
Figure Electron flow during Fe2+ oxidation by the acidophile Acidithiobacillus ferrooxidans. In
(pH 6) +
ATP
NADH
Cell material
ADP
ATP
Figure 13.24

5. Figure 13.23 Iron-oxidizing bacteria.

6. 3.17 Nitrogen Fixation (Sec 3.17 also pp 438-439)
Living systems require nitrogen in the form of NH3 or R-NH2
“Fixed” or “reduced” nitrogen, not N2
Only some prokaryotes can fix atmospheric nitrogen: diazotrophs

7. 3.17 Nitrogen Fixation
Some nitrogen fixers are free-living, and others are symbiotic
Cyanobacteria are free-living
nitrogen fixers
Soybean root nodules contain
endosymbiotic
Bradyrhizobium japonicum

8. 3.17 Nitrogen Fixation Energetically expensive (8 ATP per N atom)
Requires electron donor, often pyruvate
Utilizes leghemoglobin
Reaction is catalyzed by nitrogenase
Sensitive to the presence of oxygen
Fe plus various metal cofactors
Can catalyze a variety of reactions