Forest Preserve District of Cook County, Illinois
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Useful Bacteria
Nature Bulletin No. 217-A   February 12, 1966
Forest Preserve District of Cook County
Seymour Simon, President
Roland F. Eisenbeis, Supt. of Conservation

Most of us think of bacteria as "germs" -- unseen threats to our health and welfare. But for each of the few disease-producing kinds which can live in the human body, there are hundreds of others upon which we depend for our very existence. Bacteria help us digest our food. Without bacteria we would have no food.

They belong to the vegetable world, being minute one-celled colorless plants so small that the dot over this "i" can cover nearly a million of some kinds. Some are rod-shaped, some are round, some are corkscrew or spiral-shaped, some have hair-like whip-like filaments with which they swim actively in fluids. Most kinds multiply by simply splitting in two: each bacterium dividing into two equal "daughter" bacteria every 20 or 30 minutes, under favorable conditions. Though microscopic in size, they can multiply so fast that, after a day and a half, the billions of billions of offspring of a single one would load a long freight train -- if it were possible to feed so many. Under unfavorable conditions, some kinds form thick-walled spores which can withstand prolonged drying, extreme cold, and even boiling; and may lie inactive for days or even years.

All animals depend upon plants, directly or indirectly. Plants depend upon the fertility of the soil, which in turn depends upon bacteria. Inconceivable numbers of them inhabit the soil -- roughly a billion per teaspoonful -- where some convert plant and animal remains into humus and plant food, and others make the minerals in the soil available as plant food. All decomposition and decay in the dead bodies of plants and animals are caused by bacteria and their close relatives: molds, fungi and yeasts. Our huge garbage dumps are decomposed by them. Our modern methods of sewage disposal employ speeded-up bacterial action to rapidly break down and oxidize household and industrial wastes. Nothing escapes these scavengers. They are in the ground, in the water, in the air -- everywhere.

Nitrogen in the form of nitrates is an essential plant food frequently lacking in soils. Nitrogen from the air is inert and difficult to change and combine with other substances, but certain bacteria have the rare ability to absorb it and change it into forms which other plants and animals can use. Some of these nitrogen-fixing bacteria live in nodules or lumps on the roots of legumes such as clover, alfalfa, peas, beans and locust trees.

Fermentation, as when wine and cider turn into vinegar, is caused by bacteria. Of hundreds of different kinds, a few of the common bacteria are those used to make rye bread, sauerkraut from cabbage, pickles from cucumbers, silage from corn, linen from flax, glycerin, citric acid, lactic acid, and dairy products.

Fresh warm milk is an ideal food for many kinds of bacteria, especially the common one which causes milk to sour and curdle. Cream so soured and ripened is easily churned into butter. Cottage cheese is made from sour milk. Most cheeses are made from curds produced by treating milk from cows, sheep or goats with "rennet", a digestive ferment. The ripening, and the different textures and flavors, are accomplished by various pure cultures of bacteria and molds which are added to the curd as "starters", depending also upon special conditions of air, moisture and temperature. Some extremely hard Italian cheeses contain little water and are correspondingly slow to ripen. "Soft" cheeses contain more water and ripen more rapidly. The blue-green mold of Roquefort is due to powdered bread mold sifted into the curd. The holes in Swiss cheese come from gas generated by bacteria.

The bacteria in Limburger are little stinkers.

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