VI.

Importance of Prokaryotes

Prokaryotes play significant roles in our daily lives. In a process called nitrogen fixation, many species of cyanobacteria convert atmospheric nitrogen to nitrogenous compounds that other organisms use as food sources. Moreover, the photosynthesis occurring in cyanobacteria still contributes substantial amounts of oxygen to the atmosphere and stores the Sun’s energy in carbohydrate molecules. Cyanobacteria are the foundation for aquatic ecosystems, providing food for protozoa and other aquatic organisms. Cyanobacteria are threatened, however, by ultraviolet radiation, which penetrates the atmosphere as a result of the thinning ozone layer.

Other prokaryotes act as recyclers of carbon, nitrogen, phosphorus, sulfur, and other elements. Many prokaryotes have medical and economic importance to humans. For instance, disease-causing bacteria have played a significant role in human history, causing diseases such as tuberculosis, gonorrhea, plague, whooping cough, pneumonia, syphilis, and botulism. Certain bacteria, including the soil bacteria Actinomycetes, produce antibiotics. Other bacteria are used industrially to synthesize vitamins, enzymes, organic acids, and food products and to produce drugs by the processes of genetic engineering. Archaebacteria support ecosystems in hot springs and hydrothermal vents, where a variety of organisms feed on them. Methane-producing archaebacteria are used widely in sewage treatment plants to convert sewage sludge into methane (see Bioremediation).