Biology- Bacteria

What Are Bacteria?

Bacteria consist of only a single cell—but don't let their small size and seeming simplicity fool you. They are an amazingly complex and fascinating group of organisms. Bacteria have been found that can live at temperatures above the boiling point and in those that would freeze your blood. They "eat" everything from sugar and starch to sunlight, sulfur and iron. There is even a species of bacteria that can withstand blasts of radiation 1,000 times greater than those that would kill a human being. What Do They Look Like? There are thousands of species of bacteria, but all of them basically fall into one of three different shapes. Where Are They Found? B acteria live on or in just about every material and environment on Earth from soil to water to air, from inside your house to arctic ice to volcanic vents. Each square centimeter of your skin averages about 100,000 bacteria. Some microbes live on our skin and protect us from harmful agents.  What Do They Eat? Some bacteria are photosynthetic—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 food you've digested. Bacterial structure A structure that is vital to bacterial survival is its unique cell wall. It defines the shape of the bacterium, gives it mechanical strength and protects it from environmental changes. Bacteria are classified according to the single cell's shape and size, and the way in which the cells organized. Some bacteria have unique additional structures: Capsule—protects the bacterium from phagocytic cells, which are part of the host’s defense mechanism. . Flagellum—a structure used for locomotion. How Do They Move? Some bacteria move about in 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 of flagellar rotation so that they tumble about in one place. Other bacteria secrete a slime layer and ooze over surfaces like slugs. Yet others are fairly stationary. Friendly Bacteria We are used to thinking of bacteria as disease-causing agents. Indeed, bacteria are at the origin of various worrisome diseases. However, it is important to point out that, in contrast to popular opinion, only a small number of the thousands of bacterial species are pathogenic, meaning disease-causing. Most bacteria do not harm humans at all, and many species of bacteria are even beneficial and vital to our health. The bodies of humans and animals serve as a natural environment for bacteria. The bacteria that live in our bodies produce and provide us with different vitamins. For instance: In the human digestive system, there are different species of friendly bacteria which take part in an important and inseparable way. These bacteria are vital to the metabolism of food, the production of enzymes and vitamins (e.g., bacteria that manufacture vitamin B or vitamin K), the demolition of disease-causing microorganisms including fungi, and the regulation of intestinal acidity. These bacteria play a decisive role as symbionts in most multicellularorganisms. Bacteria that live in ruminants' digestive system break down cellulose to its monosaccharide components, releasing usable energy in the process. Not only do the bacteria located at the entrances to the body (for example the mouth, skin and woman's vagina) not cause damage, they also do not allow disease-causing microorganisms to settle there or to invade our bodies through these entrance points.   he essential uses of bacteria for humans can be seen in the environmental protection arena: Sewage-disposal facilities are aided by bacteria in the breakdown of many waste products (not only organic) and in the neutralization of some of the toxic substances that make their way into sewage. Bacteria play an important role in the biological view of pest control—as the natural enemies of different organisms that damage food crops and the agricultural industry. Several bacteria play a major role in modern genetic-engineering techniques: by inserting specific genes into the bacterial cell, the bacteria can be induced to produce the protein which these genes encode. These proteins can then be used to produce medicines and other vital substances, such as hormones. Another use of bacteria is in the making of food, especially dairy products. Special fermentation bacteria convert milk to products such as cheese, cultured milk and yogurt, the manufacture of which would be impossible without them.                                            Internal Structure Bacteria have a very simple internal structure, and no membrane-bound organelles. Nucleoid: DNA in the bacterial cell is generally confined to this central region. Though it isn’t bounded by a membrane, it is visibly distinct (by transmission microscopy) from the rest of the cell interior. DNA- Deoxyribo Nucleic Acid is single long circular molecule. It contains all genetic information for the structure & function of a bacterium under its optimum conditions. Ribosome Ribosome gives the cytoplasm of bacteria a granular appearance in electron micrographs. It is important in translating the genetic massage in messenger RNA ( Ribo Nucleic Acid) into the production of peptide sequences (proteins). It is responsible for protein synthesis. Storage Granules Nutrients and reserves may be stored in the cytoplasm in the form of glycogen, lipids, polyphosphate, or in some cases, sulfur or nitrogen. Endospore Some bacteria, like clostridium botulinum, form spores that are highly resistant to drought, high temperature and other environmental hazards. Once the hazard is removed, the spore germinates to create a new population. Capsule This layer of polysaccharide (sometimes proteins) protects the bacterial cell and is often associated with pathogenic vacteria because it serves as a barrier against phagocytosis by white blood cells. Outer membrane This lipid bilayer is found in Gram negative bacteria and is the source of lipo-polysaccharides (LPS) in these bacteria. LPS is toxic and turns on the immune system of, but not in Gram positive bacteria. Cell wall This is the complex & semi-rigid outermost layer. It gives shape to the bacterial cell & protects it from external environment. It is composed of peptidoglycan (polysaccharides + protein); the cell wall maintains the overall shape of a bacterial cell. Periplasmic Space This cellular compartment is found only in those bacteria that have both an outer membrane and plasma membrane (e.g. Gram negative bacteria). In the space are enzymes and other proteins that help digest and move nutrients into the cell. Plasma membrane This is a lipid bilayer much like the cytoplasmic (plasma) membrane of other cells. There are numerous proteins moving within or upon this layer that are primarily responsible for transport of ions, nutrients and waste across the membrane. Appendages: Bacteria may gave the following appendages ( a tail or a limb attached to a major part): Pili: These are hollow, hair like structures made of protein allow bacteria to attach to other cells. A specialized pilus, the sex pilus, allows the transfer from one bacterial cell to another. pili (sing; pilus) are also called fimbriae (sing; fimbria). Flagella The purpose of flagella (sing; flagellum) is motility. flagella are long appendages which rotate by means of a “motor” located just under the cytoplasmic membrane. Bacteria may have one, a few or many flagella in different positions on the cell.