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Harmful bacteria
Pathogenic Bacteria
These bacteria cause great losses to plant and animal population by causing several diseases.
Reduction of Soil Fertility
Some facultative anaerobic bacteria are available mostly in the oxygen deficient soil which reverse the nitrifying process, thereby causing the loss of a part of its combined nitrogen. They break down the nitrates in a stepwise manner either to ammonia through assimilatory nitrate reduction or to N2 through dissimilatory nitrate reduction.
Spoilage of Food
In favourable temperature and humidity, bacteria can grow luxuriantly in many food materials. They change the flavour, appearance and smell of food.
Different species of Streptococcus, Micrococcus and Lactobacillus cause spoilage of milk and different milk products. The exotoxin produced by Clostridium botulinum causes botulism disease showing the symptoms like swelling of tongue, double vision and respiratory disturbances.
Pollution of Water
Some bacteria pollute water and make it unsuitable for drinking. Diseases like cholera (Vibrio cholerae), typhoid fever (Salmonella typhi) and bacillus dysentery (Shigella dysenteriae) are commonly transmitted by drinking water.
Biological Warfare
Bacteria causing diseases like anthrax, black-leg, tuberculosis, etc., are used as secret war-agents.
Useful bacteria
Increase Soil Fertility
Plants do not have the efficiency of direct utilisation of huge amount (78%) of atmospheric nitrogen. However, some free-living and symbiotic bacteria are able to fix free nitrogen into nitrogenous compounds.
Industrial Importance
From ancient time men have used microorganisms in the preparation of their food, drinks etc.
The lactic acid bacteria are used in the preparation of butter, cheese, curd etc. The curd is prepared from milk by bacteria in two steps. They convert lactose sugar to glucose and then glucose to lactic acid, which sours the milk and coagulates the milk protein (casein) forming curd. Some bacteria used in dairy are Lactobacillus plantarum, L. acidophilus, L. bulgaricus, Streptococcus lactis, S. thermophilic etc.
Clostridium aceto- butylicum and Acetobacter aceti, the acetic acid bacteria are used in the conversion of alcohol to acetic acid, the vinegar. This was done in wooden vats and takes several weeks to complete the process.
Biological Control of Insect
Many bacteria like Bacillus thuringiensis etc., secrete proteins which are highly toxic to caterpillars and insects belonging to Lepidoptera. They are, however, nontoxic to other animals and also plants, thereby the bacteria are used as ideal agent for biocontrol of insect.
Degradation of Petroleum
Many bacteria like Pseudomonas, Micrococcus, Candida and Achromobacter are able to degrade petroleum hydrocarbon in water from different vehicles, thereby they check pollution.
Decomposition of Dead Animals: Some bacteria are, able to decompose the dead organic matters into inorganic form which mix with soil and increase the soil fertility. These inorganic substances are then absorbed by the plants as nutrients.
Uses and harms of virus
Usefull viruses
When most people think of viruses, they begin to recall episodes of colds and flu and symptoms associated with them. They identify viruses as harmful molecules flowing through their body, untreatable by antibiotics, meaning that the person will have to ride it out and treat the symptoms associated with the virus. Surprisingly, not all viruses, are harmful. Some viruses are good and serve a positive purpose.
Viruses are little microbes or organisms. They are not cells. Viruses are made up of protein, and to survive they must have a host. They are parasites that live off of other living things. Viruses are also capable of hibernating until they can find a host. They spread easily by exiting the body through sneezing or body fluids. They can be airborne or lay resting on the side of a sink or toilet. Protection against viruses is one of the reasons that handwashing is paramount.
The cowpox virus is considered as a helpful virus. Dr Edward Jenner discovered that when people became infected with cowpox, they did not get a more deadly virus called smallpox. Smallpox was responsible for many deaths and scarring when he discovered cowpox as a useful virus in 1796. Because of Dr. Jenner’s work, people are familiar with vaccinations. Because of the discovery of cowpox creating an immunity in people, vaccines were created that have ended smallpox throughout the world.
Studies have shown that when an infant is born, he or she has viruses in his or her stomach that help the baby to stay healthy. The viruses also travel through the intestinal system providing protection from harmful viruses. However, scientists have discovered that the infant has not one virus but a vast diversity of helpful viruses (2015).
Phages are viruses that can be found in mucus. Mucus plays a role in humans by capturing bacteria and foreign substances that could harm the human body. Phages attack harmful bacteria and destroy it. Also, phages are also found in human saliva and have molecules similar to antibodies. At present, researchers are taking a second look at the benefit of helpful viruses in the human body and as protection against harmful viruses.
Harmful viruses
Common human diseases caused by viruses include the common cold, the flu, chickenpox and cold sores. Serious diseases such as Ebola and AIDS are also caused by viruses. Many viruses cause little or no disease and are said to be "benign". The more harmful viruses are described as virulent. Viruses cause different diseases depending on the types of cell that they infect. Some viruses can cause lifelong or chronic infections where the viruses continue to reproduce in the body despite the host's defence mechanisms. This is common in hepatitis B virus and hepatitis C virus infections. People chronically infected with a virus are known as carriers. They serve as important reservoirs of the virus. If there is a high proportion of carriers in a given population, a disease is said to be endemic.
There are many ways in which viruses spread from host to host but each species of virus uses only one or two. Many viruses that infect plants are carried by organisms; such organisms are called vectors. Some viruses that infect animals, including humans, are also spread by vectors, usually blood-sucking insects. However, direct transmission is more common. Some virus infections, such as norovirus and rotavirus, are spread by contaminated food and water, hands and communal objects and by intimate contact with another infected person, while others are airborne (influenza virus). Viruses such as HIV, hepatitis B and hepatitis C are often transmitted by unprotected sex or contaminated hypodermic needles. It is important to know how each different kind of virus is spread to prevent infections and epidemics.
There are many types of plant virus, but often they only cause a loss of yield, and it is not economically viable to try to control them. Plant viruses are often spread from plant to plant by organisms (vectors). These are normally insects, but some fungi, nematode worms and single-celled organisms have been shown to be vectors. When control of plant virus infections is considered economical (perennial fruits, for example) efforts are concentrated on killing the vectors and removing alternate hosts such as weeds. Plant viruses are harmless to humans and other animals because they can only reproduce in living plant cells.