Monerans

Monerans are a group of one-celled organisms that do not have a nucleus. Along with Protists, Fungi, Plants, and Animals, Monerans make up the five kingdoms of living things. As one of the first life forms to evolve, they are today the most abundant living organisms on Earth. Monerans are found throughout the world and can live in freezing as well as extremely hot conditions.

Monerans belong to the kingdom Monera, which, unlike other kingdoms, is made up of only one member—bacteria. Monerans are usually microscopic life forms, and although some are smaller than viruses, others can be seen by the naked eye. They live not only on Earth, from hot springs to frozen wastelands, but inside other organisms as well. Nearly all multicelled plants and animals act as hosts to Monerans. Monerans are so abundant that it is estimated that the number of bacteria found in the human mouth would outnumber all of the people who have ever lived. They have left no fossil record that scientists can learn from, yet are believed to be among the oldest type of organisms still thriving. Unlike other living cells, Monerans are prokaryotic, meaning that they have no nucleus or any organelles (tiny structures inside a cell that have certain functions) inside their walls. Instead, the material that is usually found in the nucleus is scattered throughout the cell. Monerans can also reproduce asexually by binary fission, meaning that a single cell can divide itself into two identical "daughter" cells. Monerans can reach maturity in a phenomenally short time (about fifteen minutes), so that they are able to rapidly mutate or adapt to a changing environment.

TYPES OF BACTERIA

For some time, Monerans were not considered to be a separate kingdom, but advances in molecular biology now suggest that this kingdom is made up of three different types of bacteria: the archaebacteria, the eu-bacteria, and the cyanobacteria. Some scientists argue that cyanobacteria (formerly called blue-green algae) are part of the eubacteria, and that archaebacteria should form their own kingdom.

Archaebacteria. Archaebacteria are unique, since some species live in such harsh places as boiling mud, hot springs, and extremely salty water, while others live in the intestinal tracts of some mammals. The archae-bacteria called thermoacidophiles thrive in the recently discovered deep-sea volcanic vents where it is extremely hot.

Eubacteria. Eubacteria are considered to be "true" bacteria and are composed of types with which scientists are most familiar. Some make their own food as plants do, while others get their energy by fermentation (a process by which cells break down sugar and starch into energy). Others are considered dangerous parasites. The bacteria in the soil that are able to "fix" or capture nitrogen from the air are eubacteria, as are those that live in ticks and cause Lyme disease and Rocky Mountain spotted fever. These bacteria are also responsible for such transmissible diseases as syphilis and gonorrhea, as well as botulism and diarrhea. Although sometimes harmful, eubacteria also can be beneficial. For example, the bacteria Escherichia coli that normally lives in the gut of mammals produces enzymes that help with the digestion of fats. Eubacteria also are necessary for the production of cheese, yogurt, and other fermented milk products.

Cyanobacteria. Cyanobacteria are a group that make their own food by photosynthesis. Also called blue-green algae, they use the process that plants employ of capturing the energy of the Sun and changing it into simple food substances. Most live in or on the water's surface, either by themselves or in large clusters called colonies.

IDENTIFYING BACTERIA

Although all bacteria are prokaryotic, it is the cell wall that gives different types of bacteria their different shapes and allows biologists to identify them. The most commonly occurring shapes are round (cocci), rodshaped (bacillus), and coiled (spirillum). The bacteria with a round shape called cocci (singular, coccus) often form chains and are usually found in the human body. An example is Streptococcus mutans, which inhabits the mouth and causes tooth decay. A single rod-shaped bacterium is called a bacillus (plural, bacilli). The species Bacillus anthrax causes the cattle disease anthrax. Finally, the corkscrew-shaped bacteria are like twisted spirals and are called Spirillum (plural, Spirilla) or Spirochaete.

Despite our familiarity with the many disease-causing bacteria, most bacteria are not only harmless to human beings, but some have become indispensable. Besides the bacteria that allow us produce cheese and wine, and naturally break down and recycle our waste and sewage, bacteria have been used in medicine to produce such modern miracle drugs as antibiotics (like erythromycin and streptomycin). More and more, bacteria are used in the biotechnology industry, which is genetically altering certain bacteria so they will produce important compounds like insulin that are difficult to make artificially. As a result, the Monerans or bacteria are an important and essential part of the life cycle on Earth.

[See alsoKingdom ]