An entire kingdom of microorganisms was brought into life 3 billion years ago. Since then «the earth is a fundamentally a microbial planet, to which the micro-organisms are recent the relatively unimportant additions» (Wheelis, Mark, Principles of modern microbiology, 2008, p.1). The term microorganisms consist of bacteria, archaea, fungi, and protest, which can either be unicellular or multicellular. They first have been studied by Anton van Leeuwenhoek by the use of his own design microscope, in 1675. However, they have been an attractive source of study for many scientists, since they live in all parts of biosphere and are critical to nutrient recycling in ecosystems. Microbes in general are described as one of the most remarkable existence. «The procaryotes in particular are by very large margin the most biochemically and genetically diverse organisms on earth» (Wheelis, Mark, Principles of modern microbiology, 2008, p.23). Since the microorganisms were the first living being in earth they have an important regulatory role in ecosystem balance. Many of them contribute to the four major biochemical cycles; the carbon, nitrogen, sulphur and iron cycle. An example of carbon cycling at local scale is in ruminants where the digestion of cellulose occurs through microbial activity. These cellulolytic microbes hydrolyze cellulose to disaccharide cellobiose and glucose. Glucose then undergoes bacterial fermentation producing volatile fatty acids, CO₂ and methane. Many vitamins are synthesized at this point and microbial cells also good protein source. The nitrogen cycle is the main reservoir for nitrogen is the air where it is present as nitrogen gas. It includes three major processes of microbial nitrogen transformation; Nitrogen fixation, Nitrification and Denitrification. In case of sulphur cycle, sulphur contributes to the radiation balance of the earth. It reduces the amount of solar energy entering the earth, atmosphere and ocean system, thereby contributing to a cooling of the planet. In addition, at the iron cycle Leptospirillum ferooxidans and Geobacter metallireducens unergo anaerobic oxidation of organic compounds to CO2 using Ferric iron as an electron acceptor.
Image 1: Diagram of the carbon cycle. The black numbers indicate how much carbon is stored in various reservoirs, in billions of tons. The purple numbers indicate how much carbon moves between reservoirs each year.
By the time that scientists began began to understand the basis of their activities, the industrial microbiology has been familiar to a great development. This relatively new science describes «the isolation and description of microorganisms from natural environments, such as soil or water, and with the culture conditions required for obtaining rapid and massive growth of these organisms in large scale culture vessels commonly known as fermentors» (Casida, Industrial microbiology, 1968, p.4). Fermentation consist the central process to microbial biotech. In biochemistry the term mainly refers to the generation of energy by the oxidation of organic compounds using an endogenous electron acceptor. It can be carried out both in aerobic and anaerobic conditions. Despite the presence of oxygen, many microbes such as yeast prefer the fermentation to oxidative phosphorylation, as long as sugars are available for consumption. The production of ATP by fermentation, where the net-gain of energy is two molecules of ATP, is less efficient than oxidative phosporylation, a process whereby pyruvate is fully oxidized to carbon dioxide and the net-gain of ATP is 36 molecules. Since fermentation consists the main energy source in anaerobic conditions, it can be distinguished in three categories; the lactic acid fermentation, the ethanol fermentation and as hydrogen gas. The lactic acid fermentation is usually used in industrial microbiology to produce milk and dairy products. The non pasteurized milk will often undergo spontaneous lactic acid fermentation. During this process lactic acid bacteria convert milk sugar lactose to lactic acid. The accumulation of lactic acid inhibits the growth of other organisms and protects the food from spoilage. The different characteristic flavours and smells are due to the minor fermentation products. Role has the started culture organisms, the culture times and conditions. For instance the cheese is first prepared by that process and most of them are then ripened by secondary microbial transformations. That involves the gradual hydrolysis of milk protein, whereby proteases are released from the bacterial cells. A surface growth of white mold ripens several soft cheeses. This mold is known as Penicillium camembert whereas in blue cheese the mold Penicillium roquefortii is spread through it. In case of yoghurt the Lactobacillus bulgaricus species produces acetaldehyde which gives to yoghurt characteristic tart taste. In contrast with the lactic acid fermentation, the sugars in ethanol fermentation are converted into ethanol, carbon dioxide and cellular energy. This type of fermentation is carried out by yeasts and is responsible for the production of alcoholic beverages, the rising of bread dough and also the production of ethanol also can be used as flue. In bread the Saccharomyces cerevisiae are ferments that give lightness and texture to bread to it. Wines employ fermentation of natural sugars present in fruits. Here, the Lactobacillus oenos and other lactic acid bacteria lead to a second fermentation which reduces acidity i.e. converts malic acid to lactic acid and CO₂ (malo-acid fermentation). Beers, ales, and whiskeys are produced by fermenting grain starches by the action of enzyme amylase. Image 2: The process of Fermentation in yeast
At the other end of the scale, the hydrogen fermentation is associated with a diverse group bacteria and multi enzyme systems. It is similar to anaerobic conversion. The dark fermentation can be applied both in day and night. Hydrogen is constantly produced by organic compounds. In case of photofermentation the presence of light is necessary. Electrohydrogenesis refers to the generation of hydrogen gas from organic matter being decomposed by bacteria and it is used in microbial fuel cells. Due to the great variety of microorganisms “there is a wide range of such products solvents produced as fermentation end products, enzymes that are used in detergents or other applications, and perhaps most importantly, antibiotics” (Wheelis, Mark, Principles of modern microbiology, 2008, p.452). Image 3: Penicillium
These chemical compounds are made in nature by various microorganisms which are toxic to other microorganisms and are able to kill or inhibit them. The first antibiotic discovered was penicillin, from the Penicillium fungus. Penicillin is highly effective against Gram-positive bacteria and ineffective against Gram-negative organisms and fungi.the discover of penicillin yield to other developments such as to ampecillin and to beta-lactamase-resistant penicillins. In addition, streptomycin antibiotic derives from the actinobacterium Streptomyces griseus and kills sensitive microbes by inhibiting their protein synthesis. Generally, antibiotics are made by filamentous organism; the eukaryotic fungi and the prokaryotic actinomycetes, are known as secondary metabolists and “are only secreted as the culture enters the stationary phase and as the process of forming spores commences” (Wheelis, Mark, Principles of modern microbiology, 2008, p.452). Antibiotics have transformed the practice of medicine, since they allow effective control of bacterial infections. Moreover, microorganisms have been a benefit to wastewater treatment. The killing of pathogens is achieved by the chlorination or by irradiating the effluent with U.V light to produce ozone. This biotreatment describes «the major engineering infrastructure that scrupulously separates sewage from drinking water and that oxidizes much of the organic matter in sewage before it is released into the environment» (Wheelis, Mark, Principles of modern microbiology, 2008, p.458). The dilute solution of organic matter is a bacterial process at which microbes scavenge the organic matter, oxidize and convert it to microbial cells. The treatment process cannot occur completely, since inorganic salts released during the process. Thus, due to the various oxidations and regardless of their compositions, these effluent waters should not be able to support extensive growth of heterotrophic or autotrophic microorganisms. The further microbial oxidation of the organic matter leads to a decrease of dissolved oxygen in the water and results to less desirable types of fish or sometimes to the death of higher forms of water life. The strength of microorganisms had been obvious as well as in military biological programs, when they first have been used as biological weapons. Lethal diseases (e.g. anthrax) and incapacitating diseases (e.g. Q fever) were developed by the infection of animals. For instance the plague disease was occurred through the release of infected flies and rats into the target cities. Although this program of biological and chemical weapons was considered as an intelligent development from many countries, the international law banned it. As I mentioned before, microbes with their different activities benefit the humans. They are more than just disease causing as most people have known. A great example of this benefaction is the protective effect of normal flora. As the population of bacterial cells in our body is bigger than the one of human cells, a set of microorganisms adapted in specific body environment takes the responsibility of the protection from highly pathogenic organisms, i.e. can compete with pathogens, promote disease (e.g. dental caries), provide vitamins and eliminating toxins (e.g. Bacteroides), and also by being harmless (e.g. commensals). The skin, the respiratory tract, the urinary tract, the digestive tract are some of the regions where normal flora is highly adapted and acts. Concluding, the revolution of microbiology led to a complex and mature industry which principle role has been not only the production of a big variety of food by microbial processes, but also the development of the antibiotic industry. «Understanding the microbial basis of infectious disease also laid the foundations for effective control of transmission of intestinal diseases by modern sewage treatment» (Wheelis, Mark, Principles of modern microbiology, 2008, p.465). Furthermore, the higher standard of public health is underlined by the wastewater treatment since water is the most important potential common source of infectious diseases. However, because of the great variety of microorganisms their benefactions to human life and moreover to the ecosystem are more than the presented ones. Human well being is truly dependent on microbes (Wheelis, Mark, Principles of modern microbiology, 2008, p.465).
* Wheelis, Mark, Principles of modern microbiology, 2008
* (Casida, Industrial microbiology, 1968
* Dr Heaphy's Lecture material
* Dr Martha Clokie's Lecture material
* http://en.wikipedia.org/wiki/File:Carbon_cycle-cute_diagram.svg * http://yeastpee.com/fermentationfigure2.jpg