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Tag words:bacteria, microbes, environmental microbiology, nitrogen fixation, nitrogen cycle, autotrophy, lithotroph, anaerobic respiration, decomposition, denitrification, anoxygenic photosynthesis.








Kenneth Todar currently teaches Microbiology 100 at the University of Wisconsin-Madison.  His main teaching interests include general microbiology, bacterial diversity, microbial ecology and pathogenic bacteriology.

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The Impact of Microbes on the Environment and Human Activities (page 1)

(This chapter has 4 pages)

© Kenneth Todar, PhD

Beneficial Effects of Microorganisms

Microbes are everywhere in the biosphere, and their presence invariably affects the environment that they are growing in. The effects of microorganisms on their environment can be beneficial or harmful or inapparent with regard to human measure or observation. Since a good part of this text concerns harmful activities of microbes (i.e., agents of disease) this chapter counters with a discussion of the beneficial activities and exploitations of microorganisms as they relate to human culture.

The beneficial effects of microbes derive from their metabolic activities in the environment, their associations with plants and animals, and from their use in food production and biotechnological processes.

Nutrient Cycling and the Cycles of Elements that Make Up Living Systems

At an elemental level, the substances that make up living material consist of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), sulfur (S), phosphorus (P), potassium (K), iron (Fe), sodium (Na), calcium (Ca) and magnesium (Mg). The primary constituents of organic material are C, H, O, N, S, and P. An organic compound always contains C and H and is symbolized as CH2O (the empirical formula for glucose). Carbon dioxide (CO2) is considered an inorganic form of carbon.

The most significant effect of the microorganisms on earth is their ability to recycle the primary elements that make up all living systems, especially carbon (C), oxygen (O) and nitrogen (N). These elements occur in different molecular forms that must be shared among all types of life. Different forms of carbon and nitrogen are needed as nutrients by different types of organisms. The diversity of metabolism that exists in the microbes ensures that these elements will be available in their proper form for every type of life. The most important aspects of microbial metabolism that are involved in the cycles of nutrients are discussed below.

Primary production involves photosynthetic organisms which take up CO2 in the atmosphere and convert it to organic (cellular) material. The process is also called CO2 fixation, and it accounts for a very large portion of organic carbon available for synthesis of cell material. Although terrestrial plants are obviously primary producers, planktonic algae and cyanobacteria account for nearly half of the primary production on the planet.  These unicellular organisms which float in the ocean are the "grass of the sea", and they are the source of carbon from which marine life is derived.



NASA receives data from the Terra and Aqua satellites which measures net primary productivity on Earth. These false-color maps represents the rate at which photosynthetic organisms absorb carbon out of the atmosphere. The yellow and red areas show the highest rates, ranging from 2 to 3 kilograms of carbon taken in per square meter per year. The green, blue, and purple shades show progressively lower productivity. Tropical rain forests are generally the most productive places on Earth.  However, primary productivity near the sea�s surface over such a widespread area of the Earth makes the ocean roughly as productive as the land.  http://earthobservatory.nasa.gov/Newsroom/NPP/npp.html


Decomposition or biodegradation results in the breakdown of complex organic materials to forms of carbon that can be used by other organisms. There is no naturally-occurring organic compound that cannot me degraded by some microbe, although some synthetic compounds such as teflon, styrofoam, plastics, insecticides and pesticides are broken down slowly or not at all. Through the metabolic processes of fermentation and respiration, organic molecules are eventually broken down to CO2 which is returned to the atmosphere.


Waste management, whether in compost, landfills or sewage treatment facilities,  exploits activities of microbes in the carbon cycle.  Organic (solid) materials are digested by microbial enzymes into substrates that eventually are converted to a few organic acids and carbon dioxide.

Nitrogen fixation is a process found only in some bacteria which removes N2 from the atmosphere and converts it to ammonia (NH3), for use by plants and animals. Nitrogen fixation also results in replenishment of soil nitrogen removed by agricultural processes. Some bacteria fix nitrogen in symbiotic associations in plants. Other Nitrogen-fixing bacteria are free-living in soil and aquatic habitats.


Some habitats like this cactus community in the Sonoran Desert, rely on nitrogen-fixing bacteria at the base of the food chain as the source of nitrogen for maintenance of cell material. Every plant in this scene depends ultimately on biological nitrogen fixation. http://helios.bto.ed.ac.uk/bto/microbes/nitrogen.htm


Oxygenic photosynthesis occurs in plants, algae and cyanobacteria. It is the type of photosynthesis that results in the production of O2 in the atmosphere. At least 50 percent of the O2 on earth is produced by photosynthetic microorganisms (algae and cyanobacteria), and for at least a billion years before plants evolved, microbes were the only organisms producing O2 on earth. O2 is required by many types of organisms, including animals, in their respiratory processes.


The cyanobacterium, Synechococcus, is a primary component of marine and freshwater plankton and microbial mats,  The unicellular procaryote is involved in primary production, nitrogen fixation and oxygenic photosynthesis and thereby participates in the cycles of carbon, nitrogen and oxygen.  Synechococcus is among the most important photosynthetic bacteria in marine environments, estimated to account for about 25 percent of the primary production that occurs in typical marine habitats. Thomas D. Brock.

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Kenneth Todar is an emeritus lecturer at University of Wisconsin-Madison. He has taught microbiology to undergraduate students at The University of Texas, University of Alaska and University of Wisconsin since 1969.

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