Sunday, November 27, 2005
What are Bacteria?
Bacteria
Borrelia burgdorferiNelson, ASM MicrobeLibrary
Bacteria consist of only a single cell, but don't let their small size and seeming simplicity fool you. They're an amazingly complex and fascinating group of creatures. Bacteria have been found that can live in temperatures above the boiling point and in cold that would freeze your blood. They "eat" everything from sugar and starch to sunlight, sulfur and iron. There's even a species of bacteria—Deinococcus radiodurans—that can withstand blasts of radiation 1,000 times greater than would kill a human being.
Classification
Leucothrix mucor Appl. Environ. Microbiol. 55:1435-1446, 1989
Bacteria fall into a category of life called the Prokaryotes (pro-carry-oats). Prokaryotes' genetic material, or DNA, is not enclosed in a cellular compartment called the nucleus.
Bacteria and archaea are the only prokaryotes. All other life forms are Eukaryotes (you-carry-oats), creatures whose cells have nuclei.
(Note: viruses are not considered true cells, so they don't fit into either of these categories.)
Early Origins
Bacteria are among the earliest forms of life that appeared on Earth billions of years ago. Scientists think that they helped shape and change the young planet's environment, eventually creating atmospheric oxygen that enabled other, more complex life forms to develop. Many believe that more complex cells developed as once free-living bacteria took up residence in other cells, eventually becoming the organelles in modern complex cells. The mitochondria (mite-oh-con-dree-uh) that make energy for your body cells is one example of such an organelle.
What They Look Like
Ball-shaped StreptococciSimonson, ASM MicrobeLibrary
There are thousands of species of bacteria, but all of them are basically one of three different shapes. Some are rod- or stick-shaped and called bacilli (buh-sill-eye).
Others are shaped like little balls and called cocci (cox-eye).
Others still are helical or spiral in shape, like the Borrelia pictured at the top of this page.
Some bacterial cells exist as individuals while others cluster together to form pairs, chains, squares or other groupings.
Where They're Found
Bacteria live on or in just about every material and environment on Earth from soil to water to air, and from your house to arctic ice to volcanic vents. Each square centimeter of your skin averages about 100,000 bacteria. A single teaspoon of topsoil contains more than a billion (1,000,000,000) bacteria.
How They Move
Some bacteria move about their environment by means of long, whip-like structures called flagella. They rotate their flagella like tiny outboard motors to propel themselves through liquid environments. They may also reverse the direction in which their flagella rotate so that they tumble about in one place.
Other bacteria secrete a slime layer and ooze over surfaces like slugs. Others are fairly stationary.What They EatSome bacteria are photosynthetic (foe-toe-sin-theh-tick)—they can make their own food from sunlight, just like plants. Also like plants, they give off oxygen. Other bacteria absorb food from the material they live on or in. Some of these bacteria can live off unusual "foods" such as iron or sulfur. The microbes that live in your gut absorb nutrients from the digested food you've eaten.
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Bacteria are very small, single-cell organisms which occur as little round balls, tiny short sticks, or spirals that look like springs. These three basic forms are often stuck together in long strings, or clusters that look like little squares, cubes, or random grape-like clusters.
Size of Bacteria
An individual bacterium is very tiny. They are usually one or two micrometers across. Since micro means 1/000,000 (one-millionth), they are commonly one millionth of a meter in diameter. A meter is 39.37 inches (3.33 inches longer than a yard). How many bacteria lying snugly side-by-side would it take to reach one meter? Since they are one to two micrometers wide, it would take about one million lying side by side to reach one meter, or 500,000 if they were 2 micrometers wide.
Shapes of Bacteria
While some bacteria are small spheres, others are shaped like tiny hotdogs (frankfurters, or sausages). Some species of bacteria hang together in chains like a chain of sausages. Often these chains contain only a few cells, but some form chains of hundreds of cells. The hotdog shaped bacteria are usually 2 or 3 times as long as wide, but some are very long in comparison to width. Some individual cells are long shaped like a needle.
Many species of bacteria reproduce by a wall forming across the cell dividing the orginal cell into two daughter cells having the same shape and genetic composition. Since the cells are growing, by the time division (fission) is completed each of the daughters may be as large as the mother cell was before it began fission (splitting).
Arrangement of Bacteria
Some bacteria can divide every 12 to 20 minutes. Often they hang to together by the outer membranes (skin of the sausage) for a while. Suppose that the bacteria in a culture are dividing every 20 minutes on average. Suppose they then hang together for 10 minutes before becoming separated. If you draw time-diagram, you can see that about half the cells will be singles and half doubles (diploid).
Some daughter cells hang together for a long time and form long flexible chains. In some species, the the cross walls do not pinch of off for a long time and long rigid filaments form. In fact, some genera of bacteria are notable for forming long chains which which to not break apart until the culture runs out of food and is dying.
While round bacteria also form chains, some species form squares or cubes. Imagine a single round bacterium which divides and the two cells hang together. Then each of the daughter cells divides in the same plane. You now have a short chain of 4 cells. Alternatively, Suppose the second set of cell fissions occur at right angle to the first, you would now have four cells in a sqare packet. Suppose each cell then divides in the 3rd plane, you now have a cube-shaped packet of 8 cells. After 3 more divisions you have a large packet of 64 cells, but with the microscope you can usually see they are really 4 cubes of 16 cells each.
This was very long story about fission of bacteria. But you can see that the shape and arrangement of bacteria can give you some idea of the genus of an unknown bacterium by looking at the shape and arrangement of cells in a growing culture. However, toy microscopes do not have the resolution to see bacteria and I do not recommend a beginning student buy such cheap instruments. You will be disappointed. It is better to find a doctor, teacher, or lab technician who will take some time to let you look thru his microscope at some bacteria. However, it is difficult to find cultures in the optimum condition to show cubic packets, chains, etc. on the same day because your mentor in not likely to be working with so many different kinds of bacteria on the day you visit.
How Bacteria Eat
Bacteria do not have a mouth. They make proteins called enzymes inside the cell and these travel thru the cell wall into the surrounding medium. The enzymes chop the food into tiny subunits which then come into the bacteria cell by osmosis or active transport. Active transport is the process by which the cell grabs a molecule of glucose or other food and pulls it in thru the cell wall. Many specialized proteins and other molecules made by the bacterium are involved in this active transport process. Perhaps someday you can figure out ways to study the mechanisms of active transport.
The process by which the enzyme chops the food into subunits is also very complex and specific and usually requires one molecule of water for each split. If water is consumed, the chopping process is called hydrolysis (splitting by water).
The enzyme which is able to hydrolyse lactose (milk sugar) will not fit into a protein molecule the right way to be able to hydrolyze protein. Further, lactase (an enzyme able to hydrolyse lactose) will not be able to fit into a starch molecule to split it. Thus, if a bacterium is going to eat many kinds of foods, it must have many kinds of hydrolases because enzymes do very specific jobs.
Some bacteria have many kinds of enzymes and can eat many kinds of foods. Other bacteria have few enzymes and are able to digest very few kinds of food. Bacteria which do not have the correct enzymes can still live off a given food by growing where other bacteria have ready broken the food down. This is similar to a gull eating bits of sealion meat left by a shark that killed the sealion. Thus, in food processing we might used a "mixed culture" and get an especially delightfully tasting and digestible food. This website has some very interesting experiments like this for the home fermentation of special foods.
We have just learned that bacteria differ in the foods they are able to digest and that is one of the ways we can tell them apart. For example some species of Clostridium are able to digest carbohydrates and make alcohols and very smelly organic acids but can't digest proteins. Other Clostridium species can digest proteins and cause serious problems in human wounds, but do not digest carbohydrates. A few Clostridium species can digest proteins and carbohydrates. Thus, trying to grow an unknown Clostrium species upon separate carbohydrate and protein media can help us identify the unknown species.
Why would anyone want to know the name of a Clostridium? Simple, some Clostridium species are harmless and some are human pathogens (causing disease in humans). Suppose a doctor found a Clostridium in a deep wound in your body, you would suddenly be very interested wouldn't you. Or suppose you want a career helping other people; you might want to learn such thing so you could be a bacteriologist or doctor. Or you might want to study the bacteria which can ferment coarse seeds like soybeans to make a fine, tasty cheese-like food to add zest to the diets of all nations able to grow or buy soybeans.
What Bacteria Eat
There are hundreds of species of bacteria and it is possible to find a bacterium able to eat anything from sugar, to corn proteins, to soybean oil, to iron nails, to sulfur, to the compounds in wood. Yes, it is possible to find a bacterium able to do each of these. In fact, it has long been known that bacteria were involved in transforming soluble iron ions ( ) into the insoluble compounds of iron ores. Just as animals breathe oxygen to burn (oxidize) their food Thiobacillus(error not thibacillus) bacteria "breathe" (use) sulfur to oxidize their food. Each organism is using the named element as an electron acceptor to complete its electron transport pathway which generates ATP the high energy posphate that most organisms use for energy.
Most of them must find foods such as sugars, proteins and vitamins to live. The blue-green bacteria (some times called blue-green algae) have chlorophyll and can make their own food from light energy + carbon dioxide. Some other bacteria have red chlorophylls and can use light and carbon dioxide to make the sugars they need. Like all living things bacteria require mineral salts such as magnesium, calcium, iron, and others. Some bacteria are able to obtain the energy they need by oxidizing iron or sulfur. Some bacteria need sugars, vitamins, aminoacids, and other growth factors already digested and ready to use. Other bacteria can digest proteins down to amino acids and digest complex carbohydrates such as starches and table sugar down to simple sugars. Some bacteria can make their own amino acids and vitamins from carbohydrates. The metabolic abilities of bacteria are among the traits we use to group them into genera.
Bacteria species differ greatly in the conditions they need for growth. Some grow best in cool places such as soil or bodies of water, but others are able to grow in hot springs, hot water heaters, or undersea volcanoes. The bacteria which cause disease in mammals and birds, usually grow best at body temperatures. Many bacteria which cause diseases in hydra, snakes, turtles, and other cold-blooded animals, are not able to cause disease in birds or mammals because the high body temperatures kill these bacteria or limit their growth. This web site offers several pages of experiments to study the effect of pH, temperature, osmotic pressure (salt and sugar concentrations), oxygen concentration, and other environmental factors upon the growth of bacteria.
As you can imagine from this discussion, the numerous species of bacteria live in an astonishing variety of places and live on every food you can imagine. Some can eat gasoline and other
Lets begin our study of bacteria by considering the balance of nature. If there is food, some organism will eat it. If there is a place to live, some organism will live there. Every species has a great ability to produce offspring and its population expands until it runs out of food or it is limited by competition, its own waste products, or some other factor. Changes in climate or introduction of a new species from elsewhere can greatly affect the balance of nature. These simple sentences summarize the interactions of living things on earth.Bacteria are single-cell organisms and most of them must find foods such as sugars, proteins and vitamins to live. The blue-green bacteria (some times called blue-green algae) have chlorophyll and can make their own food from light energy + carbon dioxide. Some other bacteria have red chlorophylls and can use light and carbon dioxide to make the sugars they need. Like all living things bacteria require mineral salts such as magnesium, calcium, iron, and others. Some bacteria are able to obtain the energy they need by oxidizing iron or sulfur. Some bacteria need sugars, vitamins, aminoacids, and other growth factors already digested and ready to use. Other bacteria can digest proteins down to amino acids and digest complex carbohydrates such as starches and table sugar down to simple sugars. Some bacteria can make their own amino acids and vitamins from carbohydrates. The metabolic abilities of bacteria are among the traits we use to group them into genera.
Bacteria species differ greatly in the conditions they need for growth. Some grow best in cool places such as soil or bodies of water, but others are able to grow in hot springs, hot water heaters, or undersea volcanoes. The bacteria which cause disease in mammals and birds, usually grow best at body temperatures. Many bacteria which cause diseases in hydra, snakes, turtles, and other cold-blooded animals, are not able to cause disease in birds or mammals because the high body temperatures kill these bacteria or limit their growth. This web site offers several pages of experiments to study the effect of pH, temperature, osmotic pressure (salt and sugar concentrations), oxygen concentration, and other environmental factors upon the growth of bacteria.
As you can imagine from this discussion, the numerous species of bacteria live in an astonishing variety of places and live on every food you can imagine. Some can eat gasoline and other hydrocarbons. In fact, machinists face disagreeable odors on Monday morning from the accumulated waste products of microbes living in the cutting oils used to lubricate drills and cutting tools. We often say termites, cows, beavers, beetle larva, and other organisms can eat wood or sawdust. Actually, it is usually bacteria in their guts that eat the wood and the animal lives on the dead bacteria and substances they produce. In many instances, the bacteria actually live inside protozoa which live in the gut of the wood eating animal.
If some new substance comes along, a bacterium may have a little ability to eat it and that gives it a slight competitive edge because he can live when the others have run out of food. It may slightly outgrow his neighbors. Over time minor changes in genetic material occur which are called mutations. If these minor changes help an organism to grow better than its competitors, that organism may outgrow his neighbors. That is one reason the balance between living things on earth slowly changes. Mutations are constantly occurring. Nearly all mutations are harmful, meaning the change is not quite as good as the original, but some mutations give an organism an advantage over his neighbors. Genetics is the science of studying genetic material. Bacteria are good subjects for studying the basic laws of inheritance because they grow rapidly and and have traits which are easily studied.
Bacteria are important in food preparation and preservation. Firstly, many species would love to eat our food and we must find a way to keep them out or slow their growth. For example, foods retain their value longer when frozen because few bacteria can grow in a freezer, and the low temperature also slows biochemical reactions. Secondly, certain bacteria have specialized metabolisms which are ideal for food fermentations. For example, man has found many species which can digest sugars but not proteins. These species are very useful in food preparation if they produce acids which slow the growth of other organisms which would eat the proteins. Bacteria and yeasts which produce alcohols preserve foods because the alcohol kills other organisms or slows their growth. Primitive peoples around the world have developed an interesting variety of fermented foods: cheeses, drinks, breads, fish pastes, nut pastes, and others. These primitive foods sometimes cause disease because they contain pathogens such as TB, or toxic substances. Food microbiologists interested in producing safe versions of the primitive foods begin by isolating the microbes which cause the desired reactions and flavors. Then they add pure cultures of these organisms to clean raw food to produce safe, wholesome cheeses, breads, and other foods.
From the above, it is clear that the detailed study of bacteria may involve studying chemistry, botany, zoology, genetics, biochemistry, and other sciences. Even the use of mathematics and computers can enhance your bacteria science project. This web site will provide information and links to all those areas. Just begin something and let your interests lead you where they may.
Microbial safety precautions should be considered from the very beginning of your microbiology project. Most bacteria are harmless and many of those living on our skin help protect us and many species living in our gut are beneficial. For example, bacteria in the human gut produce vitamin K which is essential for normal clotting of blood.
Be sure to read our safety pages before you begin any experiments. Discuss your project with your parents and teachers and work out a safety plan before you begin. Helping your parents prepare and cook ordinary foods will give you valuable safety lessons because cuts, burns, and abrasions are the most common injuries in microbial projects.
Bacteria
