How would you convince a friend that microorganisms are more than just disease causing agents?

When discussing microorganisms the topic that always immediately comes to mind is disease, this is due to the constant bombardment of life threatening pathogens in the media, whether it is the discovery of a new drug resistant strain of a previously easily treatable condition such as the recent outbreaks of extreme drug resistant tuberculosis or the annual concern about the influenza virus, the so called ‘good bacteria' are always overshadowed by the disease causing agents. It is estimated that there are around 107 - 109 different species of bacteria alone and only a small percentage of these are considered to be pathogenic, some species have no effect on us whatsoever and some species are very useful to us. The use of microbes in the modern day industry is vital to our everyday lives and it is the aim of the essay to show this, from the water we drink, food we eat and medicine we take. It is important to realise that all life beyond the microscopic level would not exist if it wasn't for the activity of the microorganisms billions of years ago.

Let us start at the very beginning around three and a half billion years ago, the Earth was covered with highly active volcanoes which released reducing gases such as carbon monoxide, hydrogen and methane with only one percent of oxygen. A group of autotrophic bacteria called the cyanobacteria began to photosynthesise in the coastal waters of the primitive continents via the reaction shown below [1].

Carbon dioxide + water à glucose + oxygen

This process allows the cyanobacteria to make their own energy source in the form of glucose and release oxygen as a by-product, this increased the atmospheric concentration of oxygen from one percent to twenty one percent i.e. from a reducing atmosphere to an oxidising one and was essential for the development and evolution of life as we know it. In order for photosynthesis to occur the cyanobacteria use chloroplasts and it is believed that the chloroplasts found in plants are derived from an endosymbiotic relationship with cyanobacteria, in other words the origin of plants can also be contributed to the actions of cyanobacteria. This amazing microorganism is the oldest known fossil on earth and amazingly is still around today carrying out many other vital functions [2].

In the medical industry bacteria are used as ‘factories' to mass produce many life saving drugs such as insulin. After the discovery of insulin in the 1920s animals slaughtered for food such as cows and pigs were used as a source of insulin to treat diabetes, this method was very effective in managing the disease but there was always a risk that the patient body might recognise this animal insulin as a foreign protein and spark an allergic reaction [3]. However during the 1980s scientists developed recombinant DNA techniques, this allows us to produce a limitless supply of pure human insulin which can be used to treat diabetes patients with a significantly reduced chance of an immune response. The technique first involves isolating the mRNA sequence which encodes for the hormone insulin from a human pancreas, then by a process of reverse transcription using the enzyme reverse transcriptase this mRNA sequence is converted back into a type of DNA known as cDNA. The cDNA copy of the human insulin gene is then inserted by enzymes called endonucleases and DNA ligases into a plasmid which is a circular piece of DNA isolated from bacterial cells, the plasmid is then reinserted back into a bacterial cell, the bacteria then transcribes the cDNA in the plasmid and begins to produce large quantities of insulin. The bacteria divide by mitosis to reproduce which results in an exact copy of that bacteria being produced, so in a short period of time you will have produced millions of bacteria each of which producing vast quantities of insulin [4]. Probably the most important enzyme involved is the reverse transcriptase enzyme which was discovered in viruses, the plasmids, endonucleases, DNA ligases were all discovered in bacteria which themselves are needed for this whole process to work. This is an important example of where multiple microorganisms have been involved in a process which can be used to combat and treat disease, not cause them.

There is another class of microorganisms that have not yet been previously mentioned that have a wide range of uses in many different areas – the fungi, there is a particularly famous genus of fungi called Penicillium which is Latin for paintbrush and comes from the resemblance of the fungus to a paintbrush. As the name suggests one species of the Penicillium genus the Penicillium chrysogenum is a source of the antibiotic Penicillin. This was discovered by accident by the famous Scottish scientist Sir Alexander Fleming who one day left his window open and contaminated his Staphylococcus aureus plates (a disease causing bacteria) with the fungus. When Sir Fleming returned a few days later he noticed that the fungus had grown on some of his staphylococcus aureus plates and a large circle of the bacteria surrounding the fungal growth had disappeared [5]. This was the birthplace of antibiotics which have saved millions of lives since their commercial use all over the world and is another example of man utilising our microscopic friends in saving lives against disease.

Another member of the Penicillium genus the Penicillium glaucum was also involved in another accidental discovery of an entirely different nature. Cheese makers in the early 18th century in the village of Stilton, Leicestershire accidentally contaminated their cheese with the fungus by keeping it stored in mouldy cellars, this improved the flavour of the cheese and microorganisms are used in the production of many other foods and alcoholic drinks [6].

The alcohol in alcoholic drinks is produced by the microorganism yeast via the process of fermentation. Fermentation is an important metabolic pathway for yeast such as the Saccharomyces cerevisiae species as it enables the production of ATP without the need for oxygen, ATP is one of the most important molecules in cell biology, its chemical bonds act as an energy store which can be harnessed by the cell to carry out all energy requiring processes. The overall reaction for this kind of fermentation is shown below, the carbon dioxide given off can be used in the bread making industry to make the bread rise and as previously mentioned the ethanol that is produced can be used for the production of alcoholic drinks.

Glucose à 2ethanol + 2carbon dioxide

As you can see microorganisms have a huge role in the manufacturing of our food and drinks whether its cheese, beer, yoghurt, bread or one of many other products it is likely that microorganisms have played a key role in its production.

The subject of microbial fermentation brings us on to one of the important issues of our generation, what do we do when fossil fuel supplies have been depleted, certain aspects of the fuel crisis may be solved with the aid of microorganisms in the near future. A hydrogen fuel cell is a very efficient way of producing energy particular in vehicles, electrical energy is produced to power the vehicle and water is the only emission which is harmless to the environment. There are bacteria such as Rhodobacter sphaeroides out there that use a process known as dark fermentation to produce hydrogen from a diverse range of substrates such as chemical wastewater, so not only can these bacteria produce an unlimited supply of hydrogen to be used as fuel but they can also clean wastewaters from the industry. New groundbreaking ideas like harnessing the naturally occurring processes of microorganisms could play a key part in dramatically improving the fuel and environment crisis [7], along with many others.

Arguably the most important use of microorganisms for humans is the purification of sewage into clean water. The ability to produce clean, safe water for consumption all over the world saves lives and prevents the spread of the deadly disease causing agents. During the treatment of sewage there are many phases which make use of microorganisms one of them is a secondary treatment process called the activated sludge process, this consists of a brown floc of many different varieties of microorganisms but mainly consists of heterotrophic bacteria from different genus such as the Arthrobacter, Pseudomonas and Zoogloea [7]. The sewage acts an energy source for the microorganisms, their metabolism of the sewage organic matter has many benefits to us including; oxidizing carbonaceous matter, oxidizing nitrogenous matter and removing phosphate and gases from the sewage. The floc settles at the bottom of the tank and allows the treated water to be siphoned off, the remaining sludge can then be reused to treat more sewage [8]. The activated sludge process combined with other microorganism requiring treatments provides us with our clean and safe drinking water at all times and greatly improved the health of the developing world, which we all take for granted as there are still millions of people in the world that don't have access to clean water and die from the diseases associated with drinking contaminated water.

Microorganisms are not just utilised by humans for our own benefit but are needed by plants to nitrify the soil in which they grow in. Leguminous plants such as clover contain nodules on their roots which are home to some very important bacteria, these bacteria obtain nutrients from the plants and in return nitrify the soil for the plant to grow, this is an example of a symbiotic relationship between two organisms in which both of them gain a mutual benefit from their co existence. Examples of such bacteria include bacteria from the Rhizobium genus and even the cyanobacteria. These bacteria are able to convert nitrogen from the air into nitrates which in nature takes the force of a lightning strike or by the man made high energy demanding Haber process. If these bacteria were a disease causing agent that harmed the plant then the bacteria itself would not be able to survive, this is a case where being pathogenic would be disadvantageous for the microorganism.

Hopefully this essay has given you an insight into the other side of microorganisms, yes there are many microorganisms out there that do cause disease but there are so many other important functions for microorganisms both naturally occurring, such as nitrogen fixation and the man made processes such as recombinant DNA technology. Without these new found uses for microorganisms the world would be a very different place, the life expectancy of humans would be significantly lower, people everywhere would die from water born infections and many other types of bacterial infection without the contributions from microorganism to the medical and water industry. It is also important to remember that life as we know it would not even exist if it wasn't for the actions of microorganisms billions of years ago. With such a diverse number of species (107 - 109) of just bacteria alone, it is certain that there are many other unknown potential applications for microorganisms, some of which could come sooner than you think, such as the use of microorganisms in the production of hydrogen and there have even been bacteria discovered that can produce electricity [9]. So in summary microorganisms are not simply disease causing agents but instead are some of the most fascinating and diverse organisms in existence.


1. http://homepage.mac.com/uriarte/cyanobacteria.html

2. http://www.rocw.raifoundation.org/biotechnology/MScBioinformatics/microbilogy/lecture-notes/lecture-15.pdf.

3. http://www.endocrineweb.com/diabetes/2insulin.html

4. http://www.accessexcellence.org/RC/VL/GG/transfer_and.php

5. http://botit.botany.wisc.edu/toms_fungi/nov2003.html

6. http://fungus.org.uk/nwfg/lovaug00.htm

7. http://www.college.ucla.edu/webproject/micro7/studentprojects7/Rader/asludge2.htm

8. http://en.wikipedia.org/wiki/Activated_sludge

9. http://www.wired.com/science/discoveries/news/2006/05/70882

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