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

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

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

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 13.24 Electron flow during Fe2+ oxidation by the acidophile Acidithiobacillus ferrooxidans. In (pH 6) + ATP NADH Cell material ADP ATP Figure 13.24

Figure 13.23 Iron-oxidizing bacteria.

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

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

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