Virus and Bacteria


Virus infectious agent found in virtually all life forms, including humans, animals, plants, fungi, and bacteria.
The word Virus is from Latin which means poison. The study of virus is called Virology – a branch of microbiology.
Viruses are not considered free-living since they cannot reproduce outside of a living cell; they have evolved to transmit their genetic information from one cell to another for the purpose of replication.
Individual viruses, or virus particles, also called virions, contain genetic material, or genomes, in one of several forms.
Viruses consist of genetic material—either deoxyribonucleic acid (DNA) or ribonucleic acid (RNA)—surrounded by a protective coating of protein, called a capsid, with or without an outer lipid envelope
Unlike cellular organisms, in which the genes always are made up of DNA, viral genes may consist of either DNA or RNA. Like cell DNA, almost all viral DNA is double-stranded, and it can have either a circular or a linear arrangement. Almost all viral RNA is single-stranded; it is usually linear, and it may be either segmented (with different genes on different RNA molecules) or nonsegmented (with all genes on a single piece of RNA).

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A bacteriophage is a type of virus that destroys bacteria. It consists of a head, containing the genetic material, and a tail, which attaches to the exterior of a bacterium. The genetic material of the bacteriophage passes from its head through its tail into the bacterium. The genetic material then directs the bacterium to create new bacteriophages, which eventually burst from their host and, in the process, destroy the bacterium. The released bacteriophages attack nearby bacteria, and the infection process continues.
Viruses are between 20 and 100 times smaller than bacteria and hence are too small to be seen by light microscopy. Viruses vary in size from the largest poxviruses of about 450 nanometers (about 0.000014 in) in length to the smallest polioviruses of about 30 nanometers (about 0.000001 in).
Viruses are classified according to their type of genetic material, their strategy of replication, and their structure. The International Committee on Nomenclature of Viruses (ICNV), established in 1966, devised a scheme to group viruses into families, subfamilies, genera, and species. The ICNV report published in 1995 assigned more than 4000 viruses into 71 virus families. Hundreds of other viruses remain unclassified because of the lack of sufficient information.
The replication of virus is divided into 6 stages:
1.         Attachment
2.         Penetration
3.         Uncoating _ capsid is dissolved
4.         Replication _ synthesis of viral
5.         Assembly of viral particles
6.         Lysis _ the destruction of cells by disruption of the bounding membrane, allowing the cell contents to escape
Viral Replication
Outside of a host cell, a virus is an inert particle. Once inside a cell, a virus can replicate many times, creating thousands of viruses that leave the cell to find host cells of their own. Viruses that cause disease do so by destroying or damaging cells as they leave them.
Because viral processes so closely resemble normal cellular processes, abundant information about cell biology and genetics has come from studying viruses. Basic scientists and medical researchers at the university and hospital laboratories are working to understand viral mechanisms of action and are searching for new and better ways to treat viral illnesses.
Many pharmaceutical and biotechnology companies are actively pursuing effective antiviral therapies.
Viruses can also serve as tools. Because they are efficient factories for the production of viral proteins, viruses have been harnessed to produce a wide variety of proteins for industrial and research purposes.
A new area of endeavor is the use of viruses for gene therapy. Because viruses are programmed to carry genetic information into cells, they have been used to replace defective cellular genes.
Viruses are also being altered by genetic engineering to kill selected cell populations, such as tumor cells. The use of genetically engineered viruses for medical intervention is a relatively new field, and none of these therapies is widely available.
However, this is a fast-growing area of research, and many clinical trials are now in progress. The use of genetically engineered viruses extends beyond the medical field.
Recombinant insect viruses have agricultural applications and are currently being tested in field trials for their effectiveness as pesticides

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Viruses often damage or kill the cells that they infect, causing disease in infected organisms. A few viruses stimulate cells to grow uncontrollably and produce cancers. Although many infectious diseases, such as the common cold, are caused by viruses, there are no cures for these illnesses.
The difficulty in developing antiviral therapies stems from the large number of variant viruses that can cause the same disease, as well as the inability of drugs to disable a virus without disabling healthy cells. However, the development of antiviral agents is a major focus of current research, and the study of viruses has led to many discoveries important to human health.
Common diseases caused by virus are:
1.         Common cold
2.         Influenza
3.         Chicken Pox
4.         AIDS
5.         Bird Flue
6.         Polio
7.         Chlorosis (plants)
8.         Necrosis (plants)
9.         Vein Cleaning Disease (poplar)


Bacteria live all around us and within us. The air is filled with bacteria, and they have even entered outer space in spacecraft. Bacteria live in the deepest parts of the ocean and deep within Earth. They are in the soil, in our food, and on plants and animals. Even our bodies are home to many different kinds of bacteria.
Bacteria lack a true nucleus, a feature that distinguishes them from plant and animal cells. In plants and animals, the saclike nucleus carries genetic material in the form of deoxyribonucleic acid (DNA). Bacteria also have DNA but it floats within the cell, usually in a loop or coil. A tough but resilient protective shell surrounds the bacterial cell.
Anatomy of a Simple Bacterium
Bacteria cells typically are surrounded by a rigid, protective cell wall. The cell membrane, also called the plasma membrane, regulates passage of materials into and out of the cytoplasm, the semi-fluid that fills the cell. The DNA, located in the nucleoid region, contains the genetic information for the cell. Ribosomes carry out protein synthesis. Many bacteria contain a pilus (plural pili), a structure that extends out of the cell to transfer DNA to another bacterium. The flagellum, found in numerous species, is used for locomotion. Some bacteria contain a plasmid, a small chromosome with extra genes. Others have a capsule, a sticky substance external to the cell wall that protects bacteria from attack by white blood cells. Mesosomes were formerly thought to be structures with unknown functions, but now are known to be artifacts created when cells are prepared for viewing with electron microscopes.
The earliest bacteria that scientists have discovered, in fossil remains in rocks, probably lived about 3.5 billion years ago.
Some bacteria today are able to grow at temperatures higher than the boiling point of water, 100oC (212oF). These bacteria live deep in the ocean or within Earth. Other bacteria cannot stand contact with oxygen gas and can live only in oxygen-free environments—in our intestines, for example
Bacteria are so small that they can be seen only under a microscope that magnifies them at least 500 times their actual size. Some become visible only at magnifications of 1,000 times. They are measured in micrometers (µm) and average about 1 to 2 µm in length. Hundreds of thousands of bacteria would fit on a rounded dot made by a pencil
Bacteria not only have many uses, they also occur in diverse shapes and types. As a group they carry out a broad range of activities and have different nutritional needs. They thrive in a variety of environments.
Bacteria reproduce very rapidly. Replication in some kinds of bacteria takes only about 15 minutes under optimal conditions. One bacterial cell can become two in 15 minutes, four in 30 minutes, eight in 45 minutes, and so on. Bacteria would quickly cover the entire face of the globe if their supply of nutrients was unlimited. Fortunately for us, competition for nutrients limits their spread. In the absence of sufficient nutrients, however, many bacteria form dormant spores that survive until nutrients become available again. Spore formation also enables these bacteria to survive other harsh conditions.
1.         Binary Fission
The simplest sort of bacterial reproduction is by binary fission (splitting in two). The bacterial cell first grows to about twice its initial size.
2.         Spore Formation
In response to limited nutrients or other harsh conditions, many bacteria survive by forming spores that resist the environmental stress. Spores preserve the bacterial DNA and remain alive but inactive. When conditions improve, the spore germinates (starts growing) and the bacterium becomes active again.
3.         Genetic Exchange
Bacterial cells often can survive by exchanging DNA with other organisms and acquiring new capacities, such as resistance to an antibiotic intended to kill them. The simplest method of DNA exchange is genetic transformation, a process by which bacterial cells take up foreign DNA from the environment and incorporate it into their own DNA. The DNA in the environment may come from dead cells. The more the DNA resembles the cell’s own DNA, the more readily it is incorporated.
1.         Bacteria That Inhabit the Body:
A healthy, balanced community of bacteria is extremely important for our health. Some of these organisms protect us from disease-causing organisms that would otherwise infect us. 
Animals raised in a completely germ-free environment, without any contact with bacteria, are highly susceptible to infectious diseases if they are exposed to the outside world. Bacteria in our bodies also provide us with needed nutrients, such as vitamin K, which the body itself cannot make. The communities of bacteria and other organisms that inhabit the body are sometimes called the normal microflora or microbiota.
2.         Bacteria and Human Health:
Tooth decay provides a good example of how multiple factors contribute to bacterial disease. The human body hosts the bacteria, the diet supplies the sugars, and the bacteria produce the acid that damages the teeth.

3.         Disease-Causing Bacteria:
In most cases the bacteria that cause disease are not part of the bacteria that normally inhabit the body. They are picked up instead from sick people, sick animals, contaminated food or water, or other external sources. Bacterial disease also can occur after surgery, an accident, or some other event that weakens the immune system.
4.         Bacterial Killers:
Cholera, one of the world’s deadliest diseases today, is caused by the bacterium Vibrio cholerae. Cholera is spread in water and food contaminated with the bacteria, and by people who have the disease. After entering the body, the cholera bacteria grow in the intestines, often along the surface of the intestinal wall, where they secrete a toxin (poison). This toxin causes massive loss of fluid from the gut, and an infected person can die of dehydration (fluid loss) unless the lost fluids, and the salts they contain, are replaced.
Another major bacterial killer is Mycobacterium tuberculosis, which causes tuberculosis (TB), a disease of the lungs. Tuberculosis is responsible for more than 2 million deaths per year worldwide. Although antibiotics such as penicillin fight many bacterial diseases, the TB bacterium is highly resistant to most antibiotics. In addition, the TB-causing bacteria readily spread from person to person.
5.         Bacteria and the Environment:
Bacteria play a major role in recycling many chemical elements and chemical compounds in nature. Without such bacterial activities as the recycling of carbon dioxide (CO2) life on Earth would be impossible. Plants use CO2 to grow and in the process, they produce the oxygen humans and other animals breathe. Moreover, we would drown in garbage and wastes if bacteria did not speed the decomposition of dead plant and animal matter.

a.         Nitrogen Fixation:
Bacteria play a key role in making soil fertile. They convert nitrogen in Earth’s atmosphere into the nitrogen compound ammonia, which plants need to grow. Bacteria are the only organisms able to carry out this biochemical process known as nitrogen fixation. The bacteria able to fix atmospheric nitrogen usually live in association with plants, often integrated into the plant tissue. Bacteria in the genus Rhizobium, for example, form nodules (knobs) on the roots of beans and other plants in the legume family.
Symbiotic nitrogen-fixing bacteria, present in small nodules on the roots of beans and other legumes, help to return nitrogen to the soil, where the plant can then utilize it directly. In exchange, the bacteria in the root nodules use organic compounds supplied by the plant as an energy source.
b.         The Carbon Cycle:
Bacteria and fungi (yeasts and molds) are vital to another process that makes life on Earth possible: the carbon cycle. They help produce the gas carbon dioxide (CO2), which plants take from the atmosphere. During a part of the carbon cycle called photosynthesis, plants turn sunlight and CO2 into food and energy, releasing oxygen into the atmosphere
c.         Bioremediation:
Bioremediation refers to the use of microorganisms, especially bacteria, to return the elements in toxic chemicals to their natural cycles in nature. It may provide an inexpensive and effective method of environmental cleanup, which is one of the major challenges facing human society today.
6.         Bacteria in the Food Industry:
The dairy industry provides prime examples of bacteria’s harmful and helpful roles. Before the introduction of pasteurization in the late 1800s, dairy products were major carriers for bacteria that caused such illnesses as tuberculosis and rheumatic heart disease. Since that time regulation of the dairy industry has greatly reduced the risks of infection from dairy products.
On the helpful side, bacteria contribute to the fermentation (chemical breakdown) of many dairy products people eat every day. Yogurt, considered a healthful food, is produced by bacterial fermentation of milk. The bacteria produce lactic acid, which turns the milk sour, hampers the growth of disease-causing bacteria, and gives a desirable flavor to the resulting yogurt. Cheese also is produced by fermentation. First, bacteria ferment milk sugar to lactic acid. Then, cheese makers can introduce various microorganisms to produce the flavors they desire. The process is complicated and may take months or even years to complete, but it gives cheeses their characteristic flavors.
The variety of fermented foods we eat ranges from pickles, olives, and sauerkraut to sausages and other cured meats and fish, chocolate, soy sauce, and other products. In most of these fermentations, bacteria that produce lactic acid play major roles. Alcohol-producing yeasts are the primary fermentors in the manufacture of beer and wine, but lactic-acid bacteria also are involved, especially in making wine or cider. Bacteria that produce acetic acid can convert wine, cider, or other alcoholic beverages to vinegar.

7.         Bacteria in Mineral Extraction:
An interesting industrial process carried out by bacteria is the recovery of valuable minerals such as copper from ores.

8.         Bacteria in Biotechnology:
Bacteria have been at the center of recent advances in biotechnology—the creation of products for the human benefit through the manipulation of biological organisms.
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