Introduction
Microorganisms are crucial to human existence and to all living creatures. They many play significant roles in animal and plant life. A microorganism is a microscopic living organism. They may be single celled or multicellular.
They range from bacteria, archae, protozoa, some fungi, algae and viruses. Single-celled microorganisms were the first form of develop on Earth, some 3–4 billion years ago. They have fast rate of evolution and adaptation which have helped them to evolved and survive till today.

Benefits of microorganism
Micro-organisms are exploited extensively in the fields of medicine, agriculture, food production, waste disposal and many other industries.
We make use of some saprophytic bacteria which do not produce waste products harmful to humans. The bacterium Lactobacillus feeds on milk, turning it into yoghurt. Other bacteria and fungi help in cheese-making and are responsible for distinctive flavours. Most industrial enzymes (protein catalysts) come from micro-organisms.

Digestion
Huge numbers of bacteria, particularly Escherichia coli, live in the human colon. There are an estimated four hundred species and it has been suggested that the action of some of these on carbohydrate can contribute up to 10% of our energy requirements. Other bacteria synthesise vitamins and amino acids, and others may contribute to our resistance to disease by competing for space in the gut with harmful bacteria. It is important therefore to maintain a healthy gut flora.

Antibiotics
Many antibiotics are derived from microorganisms.
Most bacterial infections can be treated with antibiotics. Penicillin was the first antibiotic drug which was isolated from the Penicillium mould. However, as we use more and more antibiotics, some bacteria are becoming resistant to them. Example one strain of Staphylococcus aureus is resistant to all known antibiotics except one.

Vaccination
Vaccinations are an effective way of stimulating the body's defence against such diseases as diphtheria, polio, measles, mumps, german measles, tetanus, tuberculosis, hepatitis B and others. Vaccination play vital role in disease control and eradication. They contain killed or non-virulent (less pathogenic) strains of bacteria and viruses, and when these are injected into the blood, or swallowed, the body has a mild form of the disease, and is able to manufacture sufficient antibodies to acquire immunity.
This is the process of immunization.

Biotechnology
The manipulation of cells, particularly micro-organisms, to produce useful substances is referred to as biotechnology. Special strains of fungi and bacteria are developed by genetic engineering. They are grown in large fermenters where they secrete enzymes into their nutrient solution. The enzyme is isolated and concentrated for use. Examples of such enzymes include amylases for producing chocolates, fruit juices and syrups; cellulases for softening vegetables; proteases for tenderising meat and for removing biological stains when put in biological washing powders to name a few.

Food and beverage industry
Yeast is economically important in brewing and bread-making. In wine-making the yeast feeds on fruit sugars in the grapes, and in beer-making it feeds on the maltose sugar in germinating barley.
The term fermentation, is usually applied to this process of anaerobic respiration in which alcohol is produced. Controlled oxidation of alcohol can be carried out to produce vinegar (ethanoic acid). Bread-making uses the carbon dioxide produced by anaerobic respiration, not the ethanol. Starch in the dough breaks down to sugar, which feeds the yeast.
The carbon dioxide bubbles make the dough rise before it is baked into bread.

Sewage treatment
Makes use of bacteria which break down harmful substances in sewage into less harmful ones. Aerobic bacteria decompose organic matter in sewage in the presence of oxygen. Once the oxygen is used up the aerobic bacteria can no longer function, and anaerobic bacteria continue the decomposition of organic matter into methane gas and carbon dioxide, along with water and other minerals. Anaerobic micro-organisms are also being used to convert carbohydrate-rich crops, such as cane sugar and maize, into ethanol which is used as a substitute for petrol in cars.

Negative effects
Some of the harmful effects of microorganism include diseases caused my microscopic pathogens. Pathogenic microorganisms are also responsible for mortality and morbidity of life stock and plants. They also bring about economic loses by causing decay and damage to goods and food products.

Human diseases
Microorganisms are the cause of many infectious diseases. An estimated 30% of bacteria are disease causing pathogens.
According to health care experts, infectious diseases caused by microbes are responsible for more deaths worldwide than any other single cause. They include:

Bacteria: salmonella, tetanus, typhoid, cholera, gangrene, bacterial dysentery, diphtheria, tuberculosis, bubonic plague, meningococcal meningitis, pneumococcal pneumonia
Viruses: rabies, influenza (flu), measles, mumps, polio, rubella, chicken pox, colds, warts, cold sores
Protoctists: malaria, amoebic dysentery,
Fungi: athlete's foot, etc.
Many also cause disease in farm animals and commercial crops

Warfare
In recent times pathogenic microorganism have been threatened to be used as weapon of wars by terrorist groups. For example Saddam Hussein threatened use of anthrax as a germ warfare agent. This poses great threat to human life and can lead to vast scale of mortality and morbidity over a short period of time.

Contamination and Decay
Bacteria and other microorganism frequently cause contamination of food and water which lead to food poisoning and other illness. They are also responsible for spoilage and decomposition of agriculture produce causing vast amounts of economic losses to food and agriculture industry each year. In addition, they act as agents of spoilage and decomposition of clothing and sheltering material.


Summary
The microorganisms are without doubt crucial for human life. Their benefits are numerous from biotechnology to antibiotics and vaccine production. In recent times and coming future the composition and/or function of the microorganisms is being manipulated to achieve specific health benefits. However, the harmful effects of microorganisms is of equal importance. They cause enormous number of disease condition to both human and animals. They are also responsible for spoilage of food and agriculture produce. Further more, bacteria which are known for rapid evolution and it is of importance in medicine, as it has led to the recent development of super bugs, disease causing bacteria that are resistant to many antibiotics. This poses a great threat to human health.
As well is a challenge for medical and pharmaceutical industry which needs urgent solution as soon as possible.


 References
1.    life material/technologies limited, microbes and human life.
2.    Wikipedia, microorganisms, 6 October 2015.

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