Unknown to many people, bacteria play an important role in many technological fields, mainly in mining, medicine, food culture, plastics synthesis and sewage control. The overall commercial worth of bacteria in these operations is immense. It is also fascinating to see how much of a hidden effect bacteria have on our lives. One way bacteria are useful to mankind is in the production of complex organic molecules that are of used in small amounts as part of the our normal process of living, these include antibiotics, vitamins, amino acids and enzymes. By manipulating the genes of the bacteria and esuring they have ideal living conditions scientists can make the bacteria concentrate almost exclusively on producing just one chemical. These bacteria are then grown in special fermenting vats where the end product can be as much as 80% dry weight of the desired chemical. The desired chemical is then separated from the bacteria and made ready for commercial or practical use.
Bacteria have also been pivotally important in the study of genetics and genetic engineering but this is a separate and complicated subject which I am not going into here.
The bacterium Thiobacillus ferrooxidans is the important organism here. It works by catalysing the oxidation of metal sulphides, particularly copper sulphate so that they are soluble in water ie, Cu2S to 2Cu2+ and SO42-. This allows the copper to be leached out of the rock. The copper is then precipitated (brought out of solution) as a solid by passing it over iron. Copper sulphate will oxidise naturally in the presence of air in an acid environment, but only slowly. The presence of T. ferrooxidans speeds up the process by over 100x. This allows miners to extract metal from low grade ores in a relatively ecologically friendly way. T. ferrooxidans is also used in the organic leaching of gold and uranium with the help of other bacteria such as T. thiooxidans and Leptospirillum ferrooxidans. The mining of gold like this in small enclosed environmentally friendly digesters is becoming more popular.
Commercially, antibiotics are the most important of these substances (called secondary metabolites). An antibiotic is a substance that suppresses the growth of micro-organisms such as bacteria and fungi, and they are produced by some bacteria to prevent other bacteria from growing near them and using up their food. Over 8000 antibiotics are known to science, but we are always looking for more and currently (2000 AD) about 200-300 more are discovered each year. Antibiotics are used to treat diseases caused by bacteria or to prevent these diseases from occurring in the first place. The following list gives the most important antibiotics produced by bacteria. Penicillin is not on the list because it is produced by a fungus called Penicillum chrysogenum.
|Polymyxin B||Bacillus polymyxa|
Amino Acids are used in medicine to treat dietary deficiencies and in the food industry as antioxidants, sweeteners and flavour enhancers. Amino acids come in two forms one of which is the 3D mirror image of the other. They are called the D and L isomers of a particular amino acid. Living things use only the L isomer amino acids. Unfortunately, chemical methods of production produce 50% D and 50% L isomers, so half of what is produced is no use to anybody. Bacteria, however, being living things, produce only the L form. This is one of the reasons that they are so important in this industry.
Perhaps the best known commercially produced amino acid is glutamic acid which is sold as Monosodium Glutamate, MSG, a flavour enhancer. Two other important amino acid products are aspartic acid and phenylalanine. Mixed together these two become the popular sugar-free sweetener, Aspartame.
Lysine, another essential amino acid for humans, is also produced from bacteria, it is used as a food additive to enhance its nutritional value. Lysine is produced by Brevibacterium flavum whilst glutamic acid is produced by Corynebacterium glutamicum. Over half a million metric tonnes of amino acids are produced commercially each year, the table below lists a few with their uses.
|Lysine||Nutritive additive in bread|
|Glutamate||Flavour enhancer, meat tenderiser|
|Glycine||Flavour enhancer in sweet foods|
|Cysteine||Antioxidant in bread and fruit juices|
|Tryptophan and Histidine||Antioxidant|
|Methionine||Nutritive additive in soy products|
|Phenylalanine and Aspartic acid||Sweetener in soft drinks|
Enzymes are proteins that make chemical reactions go. Enzymes allow bacteria to make all the other useful molecules described in these sections. Of course, most of what you and I are made of was built by enzymes as well so they are pretty important biologically. Usually each enzyme has its own task which it does over and over and over again until it wears out, such are the building blocks of life. As well as building things up, enzymes can also break large molecules and groups of molecules down, such as the food we eat, into smaller more easily used parts. Many bacteria produce enzymes which they secrete into the world around them. These enzymes breakdown their target molecules outside of the bacterial cell, which can then be absorbed by them (See 'How Bacteria Eat'). This is useful for people who want to manufacture enzymes. Enzymes come in different types such as Proteases which breakdown protein molecules and Amylases which breakdown starch. Modern technology makes use of enzymes in many ways, you may even know of some already. Proteases are used for spot removal in drycleaning, meat tenderising, wound cleansing, desizing textiles and as detergents. While glucose isomerase is used in soft drink manufacture and cellulases are used in genetic research and forensic science.
Plastic fantastic - plastic is everywhere in our modern society. It is ideal for producing a variety of products such as containers for liquids of and all sorts other materials, machinery and plates, tables, cups, etc. However, plastic is a nuisance when it is no longer useful and is left lying around the countryside. Plastic is still a problem even if it is buried in a landfill. The reason for this is that it is not biodegradable, in other words it can not be rotted away by bacteria and fungi as is natures normal method of recycling the materials. Chemically produced plastics are made of multiple units of molecules such as Polypropylene, Polyethylene and Polystyrene, which most bacteria and fungi cannot digest or breakdown. Thi means they are non-biodegradable, and so they last for years once abandoned, an ecological waste and often an eyesore.
Plastics do not have to be a problem like this though, science has developed an answer. The chemical giant ICI is manufacturing a plastic in the UK from multiple units of a mixture of two bacterially produced molecules, Poly-B-hydroxybuterate and Poly-B-hydroxyvalerate. These molecules make a polymer just like ordinary plastic but having the essential difference that once left out in the compost or in a landfill they can be broken down by bacteria and fungi to become part of the cycle of life again. In 1998 only 600 tonnes of this plastic was produced but in the future, mass production could make it as cheap as ordinary plastics. Without doubt further research will reveal more microbial plastics to help save the environment. Why not ask your local politicians what they are doing to encourage the use of biodegradable microbial plastics. The picture (left) is a shampoo bottle sold in Europe, it is made of microbial plastic. The bacterium which does all the work is Alcaligenes eutrophas.
Vinegar is a common substance, used in pickles and other food stuffs. Its technical name is Acetic acid and it is a small molecule made from Ethanol (the alcohol in booze) by a number of species of bacteria. The bacteria actually make acetaldehyde from the alcohol first so the reaction looks like this:
CH3CH2OH to CH3CHO to CH3COOH
The bacteria involved are called acetic acid bacteria and the two most important genera are Acetobacter and Gluconobacter. Pure acetic acid can easily be made chemically, but vinegar made from wine by these bacteria has its own flavour resulting from other molecules present in the original wine. Vinegar is therefore made by bacteria rather than in chemical vats.