Nutrient Cycling Interactions

Microorganisms, in the course of their growth and metabolism, interact with each other in the cycling of nutrients, including carbon, sulfur, nitrogen, phosphorus, iron, and manganese. This nutrient cycling, called biogeochemical cycling when applied to the environment, involves both biological and chemical processes. Nutrients are transformed and cycled, often by oxidation-reduction reactions (see section 8.5) that can change the chemical and physical characteristics of the nutrients. All of the biogeochemical cycles are linked (figure 28.18), and the metabolism-related transformations of these nutrients have global-level impacts.

The major reduced and oxidized forms of the most important elements are noted in table 28.4, together with their valence states. Significant gaseous components occur in the carbon and nitrogen cycles and, to a lesser extent, in the sulfur cycles. Thus a soil, aquatic, or marine microorganism often can fix gaseous forms of carbon and nitrogen compounds. In the "sedimentary" cycles, such as that for iron, there is no gaseous component.

Carbon Cycle

Carbon can be present in reduced forms, such as methane (CH4) and organic matter, and in more oxidized forms, such as carbon monoxide (CO) and carbon dioxide (CO2). The major pools

612 Chapter 28 Microorganism Interactions and Microbial Ecology

Table 28.4 The Major Forms of Carbon, Nitrogen, Sulfur, and Iron Important in Biogeochemical Cycling

Major Forms and Valences

Significant Gaseous

Table 28.4 The Major Forms of Carbon, Nitrogen, Sulfur, and Iron Important in Biogeochemical Cycling

Major Forms and Valences

Significant Gaseous

Cycle

Component Present?

Reduced Forms

Intermediate Oxidation State Forms

Oxidized Forms

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