Info

hno2

hno2 +1/2 o2^hno3

Important in nitrogen cycle

Nitrobacter

The chemolithotrophs extract electrons from an inorganic energy source and then use the electrons to generate ATP by oxidative phosphorylation. The electrons are passed along an electron transport chain to generate a proton motive force, analogous to the processes described earlier. Molecular oxygen generally serves as the terminal electron acceptor. The amount of energy gained in metabolism depends on the energy source and the terminal electron acceptor; figure 6.25 illustrates this relationship.

Chemolithotrophs generally thrive in very specific environments where reduced inorganic compounds are found. For example, Thiobacillus ferrooxidans is found in certain acidic environments that are rich in sulfides. Because these organisms oxidize metal sulfides, they can be used to enhance the recovery of metals (see Perspective 6.1). Thermophilic chemolithotrophs thrive near hydrothermal vents of the deep ocean, harvesting the energy of reduced inorganic compounds that spew from the vents. The diversity and ecology of some of these organisms will be discussed in chapter 11.

Unlike organisms that use organic molecules to fill both their energy and carbon needs, chemolithotrophs do not require an external source of carbon. Instead, they incorporate inorganic carbon, CO2, into an organic form. This process, called carbon fixation, will be described later.

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