Gfn

proteases deamination NH3

proteases deamination NH3

Figure 6.24 Catabolism of Organic Compounds Other than Glucose The subunits of macromolecules are degraded to form the appropriate precursor metabolites.These metabolites can then either be oxidized in one of the central metabolic pathways or be used in anabolism.

electron acceptors. This is one important example of how nutrients are cycled; the waste products of one organism serve as an energy source for another. ■ biogeochemical cycling and energy flow, p. 773

Chemolithotrophs fall into four general groups with respect to their energy source (table 6.8):

■ Hydrogen bacteria oxidize hydrogen gas.

■ Sulfur bacteria oxidize hydrogen sulfide.

■ Iron bacteria oxidize reduced forms of iron.

■ Nitrifying bacteria include two groups of bacteria—one oxidizes ammonia, forming nitrite, and the other oxidizes nitrite, forming nitrate.

6.7 Chemolithotrophs

Table 6.8 Metabolism of Chemolithotrophs

Common Name of Organism

Source of Energy

Oxidation Reaction (Energy Yielding)

Important Features of Group

Common Genera in Group

Hydrogen bacteria

H2 gas

H2 + 1/2 O2^H2O

Can also use simple organic compounds for energy

Hydrogenomonas

Sulfur bacteria (non-photosynthetic)

H2S

H2S + 12 O2^H2O + S S + 1/2 O2 + h2o^h2so4

Some organisms of this group can live at a pH of less than 1

Thiobacillus

Beggiatoa

Thiothrix

Iron bacteria

Reduced iron (Fe2+)

2 Fe2+ + 12 02 + H2O^ 2 Fe3+ + 2 0H:

Iron oxide present in the sheaths of these bacteria

Sphaerotilus Gallionella

Nitrifying bacteria

nh3

NH3 + 11/2 02^HN02 + H20

Important in nitrogen cycle

Nitrosomonas

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