Bacteria Definition : What Is Bacteria ? - Health Article

Bacteria Definition : What Is Bacteria ?

What is bacteria?

The bacteria constitute a domain of single-cell, sometimes in colonies live micro-organisms. A bacterium does not have a cell nucleus, and thus is a prokaryote. The genetic material is located in the cytoplasm. The DNA containing usually consists of a single circular chromosome, often accompanied by one or more plasmids, which are also genetic information. A property of bacteria is that they are able to multiply rapidly. In addition to a single giant bacteria, bacteria are so small that they are only visible under a microscope.

 The bacteria constitute a domain of single Bacteria Definition : What Is Bacteria ?

Bacteria can mutually exchange plasmid (conjugation), by which they recombine. In this way arise constantly new bacterial strains.

Bacteria used to be called Eubacteria. In common parlance is often no distinction between Bacteria ("ordinary" bacteria) and Archaea (archeabacteria), which together form the group prokaryotes. In the taxonomy of the types of Bacteria, however, a separate domain.

Cyanobacteria or blue-green algae are among the bacteria, and not - as the name suggests - the eukaryotic algae. They are capable of photosynthesis.


Bacteria are found nearly everywhere. Most bacteria are about 1-5 microns (.001-.005 mm) long. However, the size can vary greatly by species. The parasitic Rickettsia bacterium can measure 0.1 microns (0.0001 mm), while the "sulfur-eating" bacterium giant Thiomargarita namibiensis dimensions of up to 750 micrometers (0.75 mm) can achieve. Bacteria are the smallest organisms that are still detectable with a light microscope.

The majority of bacteria are not harmful but sometimes useful for the health, for example in our intestines. They are also used in the industry to break down, for example, certain types of waste, or to make drugs.


The interior of a bacterium consisting of cytoplasm with, among others, the DNA. The cytoplasm is surrounded by a cell membrane. In most types of bacteria is here surrounded by a cell wall on the basis of peptidoglycan. Many bacteria to cell walls have a haircut or a slime layer or cell envelope. Bacteria can have further projections on the outside in the form of flagella and / or pili.

Differences between bacteria

Bacteria can in different ways be distinguished from each other.

 The bacteria constitute a domain of single Bacteria Definition : What Is Bacteria ?

Distinction in form
The shape of the bacteria is used for the automatic classification, without thereby are indicated at the same time also in kinship relationships. On the basis of shape and position, one can already a lot of bacteria distinguished from each other. For example, one distinguishes cocci, which are spherical, rods, which may have a large variation in length, diameter, and shape, and spiral-shaped micro-organisms, which have a corkscrew structure or a comma shape. The way in which the cells are located relative to each other may also be different, in that after the division, the cells often remain in a characteristic manner to each other.

Distinction for food
Between the bacteria are heterotrophic and autotrophic bacteria to be found:
  • Heterotrophic bacteria should include organic nutrients to survive. Within the group of heterotrophic bacteria can distinguish between parasites and saprophytes.
  1. If a heterotrophic bacteria have nutrients from a living thing and get this organism has downside is called the bacterial pathogen, pathogen or parasite.
  2. If the bacteria gets its food from dead material, it is called a saprophyte (sapros = rotten). These bacteria are responsible for the rotting of food.
  • Autotrophic bacteria are themselves capable of producing organic substances. They are classified according to the energy source:
  1. Fotoautotrofe bacteria get their energy through photosynthesis from sunlight. Cyanobacteria (blue-green algae or cyanobacteria) are in possession of pigment phycocyanin, which they can obtain their energy through photosynthesis. They may consist of single cells or connected to wire-shaped cell groups (colonies) in which the individual bacteria are held together by a sheath, for example, iron bacteria.
  2. Chemoautotrofe bacteria get their energy from certain substances from their environment.
Distinction of cell wall
The cell wall of bacteria consists of peptidoglycan. By means of a Gram-stain can be made visible or this layer is thick or thin. The cell wall is located inside the next cell membrane.
  • Bacteria with a thick wall peptidoglycan. These are the Gram-positive bacteria. Gram-positive bacteria do not typically have additional membrane on the outside of the casing, but several species do have an extra encased in a layer. Mycobacteria are well Gram-positive but have on the outside a hydrophobic waxy coating. Therefore, they are only good colourable with special color technique, such as the Ziehl-Neelsen stain.
  • Bacteria of the phylum Deinococcus-Thermus are Gram-positive, but do have an additional membrane on the outside. Bacteria with a thin wall peptidoglycan. These are Gram-negative bacteria, which usually have an additional membrane on the outside of the casing. The outer membrane allows these bacteria often pathogenic.
  • Bacteria without cell wall. There are bacteria that have no cell walls naturally, like the members of the Mollicutes class, which includes the Mycoplasmas. These are parasitic living bacteria that live in the cells of their hosts. In addition there are cell wall-less bacteria, which have developed from bacteria with a cell wall, under the action of antibiotics or any other chemical substance. These are referred to as L-forms.
Distinction on environment
Bacteria can make different demands on the environment to grow there. Does the environment here than some bacteria will not settle or grow. Conversely, favorable conditions can stimulate the growth and multiplication again.

To sensitivity to temperature, there are three distinct groups of bacteria:
  1. psychrophilic bacteria with a temperature range of 5 ° to 30 ° Celsius. These bacteria cause problems in the storage of food in the refrigerator, because they still grow at relatively low temperatures.
  2. mesophilic bacteria grow optimally between 15 ° and 50 ° Celsius. Most of the bacteria belong to this group, and so are the most common human pathogenic bacteria that have an optimum temperature of 35 ° to 40 ° Celsius.
  3. thermophilic bacteria of which the optimum temperature is between 50 and 60 ° Celsius is located. In hot springs were found to be bacteria that can grow at temperatures up to 90 ° C.

With regard to the sensitivity to the acidity of the area concerned can be classified as bacteria
  1. acidogen is a micro-organism which can constitute from food sources acid, which then lowers the pH.
  2. acidophilic is a micro-organism which can still grow well at low pH.
  3. alkaliphile is a microorganism that can grow well at a high pH (9-11).
Most of the bacteria grow at a neutral pH of 7, and can generally tolerate a pH range of 5 to 8.

*Osmotic value
The osmotic value is determined by the concentration of solute in the vicinity.

*Oxygen Tension
In their sensitivity to oxygen tension, bacteria are divided into four groups:
  1. aeroob- can thrive in the presence of oxygen
  2. optional anaeroob- can live both with and without oxygen
  3. aerofiel- micro-well need oxygen, but in small quantities
  4. anaeroob- can live without oxygen

Bacteria come in very many places, but 90% dwells deep underground, mostly under the sea. It is also known that some bacteria that normally live on plants, temporarily survive in an extreme environment like thunderclouds.


Bacteria multiply by binary division. The bacterium divides into two cells such that the cell content of each new cell or daughter cell is the same as the mother cell. There are bacterial species that can divide every 20 minutes under favorable conditions.


The conditions are not always ideal, but bacteria have many different strategies to survive. Under unfavorable conditions, some bacteria can form endospores: an internal capsule around a portion of the cell contents that even after decades freeze or boil an hour still managed to keep position. Under favorable conditions germinates from the endospore a new bacterium. Many pathogenic bacteria can not. Another survival strategy is that the whole bacterium encapsulates, it is called a cyst. So the bacteria can bridge a critical period because he is temporarily at rest.

Bacteria that live deep in the earth's crust to cope with limited food supply. In nutrient-poor tropical Pacific Ocean between Hawaii and Central America, living 30 meters depth some aerobic types so slow that in 1000 only a year micromoles consume oxygen per liter of water. At 20 meters depth there are approximately 1000 bacteria per cm², which is very little, at even greater depths is impossible to count them. There are bacteria known in a sediment life that is already buried 66 million years. The amount of food available was so small and the metabolism of the bacteria so slow that the bacteria only once parts of the millennium. It is thus the slowest organisms on earth. Thus, there are bacteria in the tropical Pacific which consume oxygen, but it is expected that most of these bacteria of sulfate or iron life.

Pathogens in humans

Many types of bacteria are present everywhere. Some are never problematic, some are useful, others may in severe debilitation or under special circumstances sometimes lead to symptoms of disease (pathogens), while others do it regularly. At the cellular metabolism of bacteria, poisons or toxins can arise which can sometimes be harmful to humans. You experience than on diseases such as cholera, plague, tetanus. There are a lot of bacteria which do not normally occur in or on the human being and to contact often or always lead to disease symptoms. A major duduk kasus here is that bacteria can often unnoticed spread by germs carriers who do not suffer from the bacteria but release the bacteria through feces, urine, blood and saliva.

Against diseases that are caused can usually antibiotics are used by bacteria.

The science that deals with the study of these pathogens is the medical microbiology.

Examples of these bacteria or diseases are:
  • Blue-green algae
  • Botulism
  • Legionella

Bacteria can also cause plant diseases. Fighting is not really possible because antibiotics are not available. The diseases are quite contagious. Hygienic work is the way to prevent spreading. Examples are:
  • blight
  • watermark disease
  • halo blight (bean)
  • bacterial canker (Pseudomonas syringae) of plum, peach and cherry
  • yellow sick (hyacinth)
Other bacteria live in symbiosis with plants, such as Rhizobium bacterium that forms nitrogen-fixing root nodules of legumes. Some Cyanobacteria (blue-green algae) live in symbiosis with fungi is different groups lichens.


The bacteria are distinguished by shape (morphology), diet (metabolism) and in modern taxonomy mainly to the composition of the DNA. In the course of time the bacteria have been classified in various ways. Broadly speaking, however, the formats in general are equivalent to each other.

Species are further subdivided into sub-genera (subgenus) and subspecies (subspecies). Subspecies are identified by an addition to the two-part generic, for example, Campylobacter pylori subsp. mustelae. Thus a ternary name.

We know by the bacteria also the expression strain (in English strain) in front of a pure culture of genetically identical bacteria which is derived from a particular bacterial species. Such a culture of identical bacteria is usually obtained by means of a pure culture.
When a tribe is the generic name of the original species added to a name or letter-number, for example, Lactobacillus casei Shirota and Bifidobacterium longum BB536.
The Dutch term strain but should not be confused with the English term Tribe. Tribe is a grade ranging from Family and Genus and thus has a larger number of different (but very similar to each other) species.

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