Bacteriology at UW-Madison
Beneficial Effects of Microorganisms
Microbes are everywhere in the biosphere, and their presence
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 exploitation of microorganisms as they relate to human
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.
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 that 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 rainforests 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
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
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
Microbes invariably enter into beneficial, sometimes essential, associations with all higher forms of organisms, including insects, invertebrates, fish, animals and plants. For example, bacteria and other microbes in the intestines of animals and insects digest nutrients and produce vitamins and growth factors. In the plant world, leguminous plants (peas, beans, clover, alfalfa, etc.) live in intimate associations with bacteria that extract nitrogen from the atmosphere and supply it to the plant for growth.
The mutalistic association between nitrogen fixing bacteria and legumious plants. Left. Nitrogen-fixing Rhizobium bacteria colonized on the root hairs of clover plants. Right. Nodules containing Rhizobium bacteria on the plant roots through the combined interaction between the plant and the bacterium. In the nodule the bacteria fix nitrogen. which they share with the plant. In exchange, the plant supplies the bacteria with a source of carbon and energy for growth.
The microbes that normally live in associations with humans on the various surfaces of the body (called the normal flora), such as Lactobacillus and Bifidobacterium, are known to protect their hosts from infections, and otherwise promote nutrition and health.
Lactobacillus acidophilus and a vaginal squamous epithelial cell. CDC. L. acidophilus (informally known as Doderlein's bacillus) colonizes the vagina during child-bearing years. As a lactic acid bacterium, the organism creates a low pH (acidic environment) on the tissues which prevents colonization by potentially harmful yeast and other bacteria.
Production of Foods and Fuels
In the home and in industry, microbes are used in the production of fermented foods. Yeast's are used in the manufacture of beer and wine and for the leavening of breads, while lactic acid bacteria are used to make yogurt, cheese, sour cream, buttermilk and other fermented milk products. Vinegars are produced by bacterial acetic acid fermentation. Other fermented foods include soy sauce, sauerkraut, dill pickles, olives, salami, cocoa and black teas. Yeast are also involved in fermentations to convert corn and other vegetable carbohydrates into ethanol to make beer, wine or gasohol, but bacteria are the agents of most other food fermentations.
Medical, Pharmaceutical and Biotechnological ApplicationsIn human and veterinary medicine, for the treatment and prevention of infectious diseases, microbes are a source of antibiotics and vaccines.
Left. Human insulin for treatment of diabetes. Right. Streptokinase for dissolving blood clots. Made by recombinant DNA technology. Other medical products include hormones, vitamins, vaccines, antigens, antibiotics and diagnostic agents.
Microorganisms, in particular the bacterium, Escherichia coli and the yeast, Saccharomyces, have been used as model organisms for basic research and the study of cellular life. Hundreds of thousands of scientific papers have been published on these two organisms. Because of cell theory and the unity of biological processes in all organisms, this information provides us with insight and understanding of life at all levels, including human.
Harmful Effects of Microbes
The primary harmful effects of microbes upon our existence and civilization is that they are an important cause of disease in animals and crop plants, and they are agents of spoilage and decomposition of our foods, textiles and dwellings.
Microbes Cause Infectious Disease
A microbe which is capable of causing infectious disease in an animal or plant is called a pathogen. Four groups of microbes contain pathogens: bacteria, fungi, protozoa and the viruses. Only the archaea and algae are lacking pathogens. Pathogens are the cause of infectious diseases.
(L) Borrelia burgdorferi, the bacterium that causes Lyme Disease. (R) Influenza virus, cause of flu. CDC.
Historically, infectious diseases are the most significant cause of death in humans. Until the beginning of the Twentieth Century, it is estimated that more than half the people who ever lived died from smallpox, caused by a virus, or malaria, caused by a protozoan. Bacteria, too, have been the cause of some of the most deadly diseases and widespread epidemics of human civilization. Bacterial diseases such as tuberculosis, typhus, plague, diphtheria, typhoid fever, cholera, dysentery and pneumonia have taken a huge toll on humanity.
Deaths from infectious diseases declined markedly in the United States during the 20th century. This contributed to the nearly 30-year increase in life expectancy during this period. In 1900, the three leading causes of death were pneumonia, tuberculosis (TB), and diarrhea and enteritis, which (together with diphtheria) caused one third of all deaths. In 1997, heart disease and cancers accounted for 55% of all deaths, with 4.5% attributable to pneumonia, influenza, and human immunodeficiency virus (HIV) infection . However, one of the most devastating epidemics in human history occurred during the 20th century: the 1918 influenza pandemic that resulted in 20 million deaths, including 500,000 in the United States in less than 1 year - more than have died in as short a time during any war or famine in the world.
HIV infection, first recognized in 1981, has caused a pandemic that is still in progress, affecting 33 million people and causing an estimated 13.9 million deaths. This illustrates the volatility of infectious disease and the unpredictability of disease emergence and points us to the challenges ahead.
Progress in the 20th century is based on the 19th century discovery of microorganisms as the cause of many serious diseases (e.g., cholera and TB). Disease control resulted from improvements in sanitation and hygiene, the discovery of antibiotics, the implementation of universal childhood vaccination programs, and technological advances in detecting and monitoring infectious disease.
Left: Penicillium mold growth on orange; Right: soft rot on peaches caused by the fungus Monilia.