History of the Discovery of Microorganisms PDF

1 HISTORY OF THE DISCOVERY OF MICROORGANISMS The word ―microbiology‖ was derived from three Greek words: mikros (meaning ‘small‘), bios (meaning ‗life‘) and logia (meaning ‗science or study‘). Microbiology is the study of microorganisms or microbes, which are too small to be seen by the naked (...

1 HISTORY OF THE DISCOVERY OF MICROORGANISMS The word ―microbiology‖ was derived from three Greek words: mikros (meaning ‘small‘), bios (meaning ‗life‘) and logia (meaning ‗science or study‘). Microbiology is the study of microorganisms or microbes, which are too small to be seen by the naked (unaided) eyes. The group includes bacteria, fungi (yeasts and molds), protozoa, and algae. It also includes viruses, those non-cellular entities sometimes regarded as straddling the border between life and non-life. Note however that some organisms studied in this field are visible to the eyes without a microscope such as Epulopiscium fishelsoni (bacteria), Thiomargarita namibiensis (bacteria), mushroom (fungi), mould (fungi). It is all about the study of microbial cells, how they work and affect man, plant, animals and the environment. Discovery of Microorganisms The invention of the microscope enabled the study of microorganisms. The first microscopes were simple ground glass lenses that magnified images of the tiny life. Among the first to observe this previously unseen and invisible microbial world were Robert Hooke and Anthony Van Leeuwenhoek. 1. Robert Hooke (1635-1703), an English mathematician and natural historian was the first to coin the term ―cells‖ to describe the ―little boxes‖ he observed while examining cork slices with a compound microscope. He was also the first to make a known description of microorganisms.  2 2. Anthony Van Leeuwenhoek (1632-1723) was a Dutch draper and an amateur microscope builder. He learned lens grinding as a hobby and made over 100 simple microscopes each capable of magnifying an image about 300 times. By using simple microscopes, he observed microscopic organisms which he called ―animacules‖. He discovered bacteria in 1676 while studying pepper water infusion and reported his observations in a series of letters to Royal Society of London which published them in 1684 in English translation. He made sketches of the different shapes of bacteria. He was the first person to publish extensive and accurate observations of microorganisms. He is regarded as the father of microbiology. After Van Leeuwenhoek‘s death, the study of microbiology did not develop rapidly because microscopes were rare and interest in microorganisms was not high. Scientists then were debating the theory of spontaneous generation. The Theory of Spontaneous Generation of Organisms The concept spontaneous generation states that living organisms could develop from non-living matter. The Greek philosopher Aristotle (384–322 BC) was one of the earliest recorded scholars to articulate the theory of spontaneous generation, the notion that life can arise from non-living matter. Aristotle proposed that life arose from non-living  3 material if the material contained pneuma (“vital heat”). As evidence, he noted several instances of the appearance of animals from environments previously devoid of such animals, such as the seemingly sudden appearance of fish in a new puddle of water. This theory persisted into the 17th century, when scientists undertook additional experimentation to support or disprove it. By this time, the proponents of the theory cited how frogs simply seem to appear along the muddy banks of the Nile River in Egypt during the annual flooding. Others observed that mice simply appeared among grain stored in barns with thatched roofs. When the roof leaked and the grain molded, mice appeared. Jan Baptista van Helmont, a 17th century Flemish scientist, proposed that mice could arise from rags and wheat kernels left in an open container for 3 weeks. In reality, such habitats provided ideal food sources and shelter for mouse populations to flourish. However, one of van Helmont’s contemporaries, Italian physician Francesco Redi (1626–1697), performed an experiment in 1668 that was one of the first to refute the idea that maggots (the larvae of flies) spontaneously generate on meat left out in the open air. He predicted that preventing flies from having direct contact with the meat would also prevent the appearance of maggots. Redi left meat in each of six containers. Two were open to the air, two were covered with gauze, and two  4 were tightly sealed. His hypothesis was supported when maggots developed in the uncovered jars, but no maggots appeared in either the gauze-covered or the tightly sealed jars. He concluded that maggots could only form when flies were allowed to lay eggs in the meat, and that the maggots were the offspring of flies, not the product of spontaneous generation. In 1745, John Needham (1713–1781) published a report of his own experiments, in which he briefly boiled broth infused with plant or animal matter, hoping to kill all pre-existing microbes. He then sealed the flasks. After a few days, Needham observed that the broth had become cloudy and a single drop contained numerous microscopic creatures. He argued that the new microbes must have arisen spontaneously. In reality, however, he likely did not boil the broth enough to kill all preexisting microbes. Lazzaro Spallanzani (1729–1799) did not agree with Needham’s conclusions, however, and performed hundreds of carefully executed experiments using heated broth. As in Needham’s experiment, broth in sealed jars and unsealed jars was infused with plant and animal matter. Spallanzani’s results contradicted the findings of Needham: Heated but sealed flasks remained clear, without any signs of spontaneous growth, unless the flasks were subsequently opened to the air. This suggested that microbes were introduced into these flasks from the air. In response  5 to Spallanzani’s findings, Needham argued that life originates from a “life force” that was destroyed during Spallanzani’s extended boiling. Any subsequent sealing of the flasks then prevented new life force from entering and causing spontaneous generation. Louis Jablot (1670) conducted an experiment in which he divided a hay infusion that had been boiled into two containers: a heated container that was closed to the air and a heated container that was freely open to the air. Only the open vessel developed microorganisms. This further helped to disprove abiogenesis (The origin of life from non-living matter) Disproving Spontaneous Generation The debate over spontaneous generation continued well into the nineteenth century, with scientists serving as proponents of both sides. To settle the debate, the Paris Academy of Sciences offered a prize for resolution of the problem. Louis Pasteur, a prominent French chemist who had been studying microbial fermentation and the causes of wine spoilage, accepted the challenge. In 1858, Pasteur filtered air through a gun-cotton filter and, upon microscopic examination of the cotton, found it full of microorganisms, suggesting that the exposure of a broth to air was not introducing a "life force" to the broth but rather airborne microorganisms.  6 Later, Pasteur made a series of flasks with long, twisted necks ("swan-neck" flasks), in which he boiled broth to sterilize it. His design allowed air inside the flasks to be exchanged with air from the outside, but prevented the introduction of any airborne microorganisms, which would get caught in the twists and bends of the flasks’ necks. If a life force besides the airborne microorganisms were responsible for microbial growth within the sterilized flasks, it would have access to the broth, whereas the microorganisms would not. He correctly predicted that sterilized broth in his swan-neck flasks would remain sterile as long as the swan necks remained intact. However, should the necks be broken, microorganisms would be introduced, contaminating the flasks and allowing microbial growth within the broth. Pasteur’s set of experiments irrefutably disproved the theory of spontaneous generation and earned him the prestigious Alhumbert Prize from the Paris Academy of Sciences in 1862. In a subsequent lecture in 1864, Pasteur articulated "Omne vivum ex vivo" ("Life only comes from life"). In this lecture, Pasteur recounted his famous swan-neck flask experiment, stating that "life is a germ and a germ is life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment.  7 The Golden Era of Microbiology (1860-1910) Golden era of microbiology started with the work of Louis Pasteur (France) and Robert Koch (Germany). John Tyndall (1820-1893) showed that the hay had contaminated his lab with an incredible kind of living organism. Ferdinand John (1877) demonstrated the resistant forms as small, refractile endospores, a special stage in the life cycle of hay bacillus (Bacillus subtilis). Since spores are readily sterilized in the presence of moisture at 120¬0 C, the autoclave, which uses steam under pressure, became hallmark of the bacteriology. Pasteur (1857) became interested in fermentation products and observed different kind of microbes associated with different kind of fermentation: spheres of variable size (now known as yeast cells) in the alcoholic fermentation and smaller rods (lactobacilli) in the lactic fermentation. During this Experiment, Pasteur established the study of microbial metabolism and in particular he showed that life is possible without air. Pasture explained that in grape juice the high sugar concentration and the low protein content (i.e low buffering power) lead to a low pH, which allows the outgrowth of acid-resistant yeasts and thus yields an alcoholic fermentation. In milk in contrast, the much higher protein and lower sugar content favour the outgrowth of fast growing but more acid-sensitive bacteria, which cause a lactic fermentation.This finding led Pasteur to state that specific microbes might also be causes of specific disease in man.  8 Pasteur developed the procedure of gentle heating (i.e. pasteurization) to prevent the spoilage of beer and wine by undesired microbes. This process was later used to prevent milk borne diseases of man. Of the great economic importance was the extension of industrial fermentations from the production of foods and beverages to that of valuable chemicals, such as glycerol, acetone, and later vitamins, antibiotics and alkaloids. The unity of biology at a molecular level concept was developed when it was discovered that the carbohydrate metabolism pathways are similar in some microbes and in mammals. This discovery was made towards the end of the Pasteurian era notably in Russia and Beijerinck in Holland who discovered variety of metabolic patterns by different kinds of bacteria adopted to different ecological niches. The ecological niches is defined as the physical space occupied by an organism, but also its functional role in the community. These organisms were isolated by using Pasteur`s principle of selective cultivation: enrichment culture in which only a particular energy source is provided, and growth is restricted to those organisms that can use that source.  9 The Germ theory of disease The germ theory of disease states that many diseases are caused by microorganisms such as bacteria, viruses, protozoa, or fungi. These diseases are caused by the growth and replication of microorganisms. Robert Koch and Louis Pasteur confirmed this theory in the 1870s and 1880s with a series of elegant experiments proving that microorganisms were responsible for causing anthrax, rabies, plague, cholera, and tuberculosis. Support for the germ theory of disease began to accumulate in the early nineteenth century. Agostino Bassi (1773–1856) first showed that a microorganism could cause disease when he demonstrated in 1835 that the silkworm disease was due to a fungal infection. He also suggested that many diseases were due to microbial infections. In 1845, MJ Berkeley proved that the great potato blight of Ireland was caused by a fungus. Bassi’s work served to influence Louis Pasteur, who is accredited with the germ theory of disease following his experiments demonstrating the relationship between microorganisms and disease.  10 Today, the Germ theory of Disease still remains a guiding theory that underlies contemporary biomedicine. Discovery of Viruses Researchers used special filters to remove bacteria from tissues that were infected. If bacteria were causing the infection, the filtered tissues should no longer be able to make other organisms sick. However, the filtered tissues remained infective. This meant that something even smaller than bacteria was causing the infection. Scientists did not actually see viruses for the first time until the 1930s. That’s when the electron microscope was invented. In 1915, English bacteriologist Frederick Twort discovered bacteriophage, the viruses that attack bacteria. He noticed tiny clear spots within bacterial colonies, and hypothesized that something was killing the bacteria. The tobacco mosaic virus was the first one to be seen. It was first seen with an electron microscope in 1935. Microorganisms in 20th Century The discovery of microbial effects on organic and inorganic matter started with the discovery of Theodore Schwann and others (1937) who observed that yeast cells are able to convert sugar to alcohol i.e. alcoholic fermentation. It was Pasteur’s observations that revealed about anaerobic and aerobic microorganisms. Role of microorganisms in the carbon, nitrogen and sulphur cycles in soil and aquatic  11 habitats were discussed by Sergei N. Winogradsky (1956-1953) and Martinus Beijerinck (1851-1931), The Russian microbiologist Winogradsky also discovered that (i) soil bacteria oxidize Iron, Sulphur and Ammonia to obtain energy, (ii) isolated anaerobic N2 fixers and (iii) studied the decomposition of cellulosic organic matter. On the other hand, Beijerinck, contributed a lot in the area of microbial ecology. Azotobacter, a free living nitrogen fixer was isolated. Later a root nodulating bacterium named as Rhizobium and sulphate reducers were also isolated. Both these microbiologists developed the enrichment culture techniques and the use of selective media in the microbiology. In 20th century, microbiology developed from the angle of other disciplines of biological sciences in such a way so that problems of cell structure to the evolution are solved. Although, more emphasis were laid down on the agents of infectious disease, the immune response, chemotherapeutic agents and bacterial metabolism. Beadle and Tautam (1941) used mutants of the bread mold, Neurospora while Salvadore Luria and Max Delbruck (1943) used bacterial mutants to show that gene mutations were truly spontaneous and not directed by the environment.  12 Avery, Macleod, and Mc Carty (1944) evidenced that DNA was the genetic carried genetic information. Such discoveries made microbiology, genetics and biochemistry as modern molecularly oriented genetics. Microbiology contributed maximum in molecular biology which deals with the physical and chemical aspects of living matter and its function. The genetic code and the mechanism of DNA, RNA and protein synthesis were also studied by using several microorganisms. Regulation of gene expression and the control of enzymes activity were also discussed in the light of microbiology in 1970’s new discovery such as recombinant DNA technology and genetic engineering were also led to development of microbiology which gave the service of microbial biotechnology.