Teacher resources and professional development across the curriculum

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Unit Chapters
Genomics
Proteins & Proteomics
Evolution & Phylogenetics
Microbial Diversity
Introduction
Microbes as the First Organisms
The Diversity of Microbial Metabolism
Archaea and Bacteria
The Universal Tree of Life
Studying Unculturable Microbes with PCR
Microbes and the Carbon Cycle
Microbes and the Cycling of Nitrogen
Biofilms
Biofilms Formation and Bacterial Communication
Impact of Biofilms on Humans
Communication Between Bacteria and Eukaryotes
Microbes in Mines
Microbial Leaching of Ores
Coda
Emerging Infectious Diseases
HIV & AIDS
Genetics of Development
Cell Biology & Cancer
Human Evolution
Neurobiology
Biology of Sex & Gender
Biodiversity
Genetically Modified Organisms
Microbes and the Cycling of Nitrogen

Nitrogen is an important part of proteins and nucleic acids. This vital nutrient is recycled from organic compounds to ammonia, ammonium ions, nitrite, nitrate, and nitrogen gas by a variety of processes, many of which depend on microbes. Different organisms prefer nitrogen in different forms.

Figure 6. The nitrogen Cycle

The accompanying figure illustrates nitrogen cycling. Note that nitrification (the conversion of ammonium to nitrite and nitrate) in soil is carried out by two genera of bacteria: Nitrosomonas and Nitrobacter. Denitrification - the loss of nitrate from soil to form gaseous nitrogen compounds (N2O, NO, and N2) - is dependent on other kinds of bacteria.

Some prokaryotes are essential to the nitrogen cycle because of their role in nitrogen fixation, the conversion of nitrogen gas to ammonium ions. These ions can then be used to build amino acids. In aquatic environments cyanobacteria are the most significant nitrogen fixers. In soil some nitrogen-fixing bacteria are free-living, such as members of the genus Clostridium; others live in symbiotic relationship with leguminous plants (such as peas and clover). Symbionts, such as Rhizobium, may contribute ten times more nitrogen to soils than free-living bacteria. As we shall see, these symbionts develop intimate relationships with their host plants that require complex communications.

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