2. 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

3. 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

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

5. Figure 13.24 (pH 2) (pH 6) + ATP ATP e– e– Out Outer membrane
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

6. Figure 13.23 Iron-oxidizing bacteria.

8. 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
Numerous types of prokaryotes can fix atmospheric nitrogen:
Diazotrophs
Assimilative not dissimilative

9. 3.17 Nitrogen Fixation Energetically expensive (8 ATP per N atom)
Requires electron donor, often pyruvate
Reaction is catalyzed by nitrogenase
Sensitive to the presence of oxygen
Fe plus various metal cofactors
Can catalyze a variety of reactions

10. 3.17 Nitrogen Fixation
Cyanobacteria most important nitrogen-fixers at ecological level
Numerous types and habitats: terrestrial, aquatic, marine
Can be unicellular or colonial
Most species free-living
But some cyanobacteria are symbionts

11. 3.17 Nitrogen Fixation Some nitrogen fixers are symbiotic
Rhizobia provide best example
Bradyrhizobium japonicum colonizes soybean roots
Induces plant to form
specialized structures
called root nodules
Leghemoglobin

12. Rhizobium radiobacter aka Agrobacterium radiobacter aka Agrobacterium tumefaciens is another important member but not a diazotroph
Soil bacterium that causes plant tumors called crown galls
Agro uses chemotaxis to accumulate around plant roots
Transfers some of its DNA (called T-DNA) into plant genome
In plant cell T-DNA causes synthesis of plant hormones and other compounds not usually found in plants