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274 Chapter 11 The Diversity of Prokaryotic Organisms

Table 11.3 Terms Used to Describe Microorganisms According to Their Metabolic Capabilities

Term

Definition

Comments

Chemotroph

An organism that obtains energy by oxidizing chemicals; the same process provides reducing power for biosynthesis.

Aerobic respiration uses O2 as a terminal electron acceptor, anaerobic respiration uses an inorganic compound other than O2 as a terminal electron acceptor, and fermentation uses an organic compound such as pyruvate as a terminal electron acceptor.

Chemolithotroph

Inorganic chemicals such as H2S are used as an energy source (litho- means "rock").

Generally, a chemolithotroph obtains carbon from CO2 and is therefore a chemoautotroph; because of this, the terms chemolithotroph and chemoautotroph are often used interchangeably. Alternatively, and more correctly, the term chemolithoautotroph is used.

Chemoorganotroph

Organic compounds such as glucose are used as an energy source.

A chemoorganotroph obtains carbon from organic compounds and is therefore a chemoheterotroph; because of this, the terms chemoorganotroph and chemoheterotroph are often used interchangeably.The term chemoorganoheterotroph is rarely used, although it is technically more correct.

Phototrophs

Organisms that harvest energy from sunlight; cells need a source of electrons to make reducing power for biosynthesis.

Anoxygenic phototrophs use reduced compounds such as H2S as a source of electrons for reducing power. Oxygenic phototrophs use H2O as a source of electrons for reducing power, generating O2.

Photoautotroph

Energy is harvested from sunlight; carbon is obtained from CO2.

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