General Microbiology
Total Page：16
File Type：pdf, Size：1020Kb
GENERAL MICROBIOLOGY Microbial World, History and Development of Microbiology, Scope of Microbiology Dr. (Mrs) S. Sharma Professor Department of Microbiology CCS Haryana Agricultural University Hisar-125001 and Dr. Neeraj Dilbaghi Reader Department of Biotechnology Guru Jambheshwar University of Science & Technology Hisar-125001 01-May-2006 (Revised 12-Dec-2006) CONTENTS Introduction Historical Developments Leeuwenhoek’s Findings Biogenesis versus Abiogenesis Contributions of Pasteur Contributions of Robert Koch and Germ Theory of Disease Rise of Medical Microbiology Microorganisms as Geochemical Agents Microbiology in the Twentieth Century Activities of microorganisms important in our daily life Scope of Microbiology Some recent applications of bacteria Keywords Microorganisms, microscope, fermentation, disease Introduction Microbiology, the study of microscopic organisms, derived its name from three Greek words: mikros (“small”), bios (“life”), and logos (“science”). Taken together they mean the study of microorganisms which are very small and cannot be seen by unaided eye. If an object has a diameter 0.1 mm or less, eye cannot see it and very little details can be seen in an object having diameter 1 mm. So roughly speaking organisms having diameter 1 mm or less are called microorganisms and are studied in Microbiology. Although microorganisms are ancient by many standards, microbiology itself is a comparatively new science. The existence of microorganisms was unknown until the discovery of Microscope. Microscope is an optical instrument which can magnify small objects which cannot be seen by naked eye. Microscopes were invented in the beginning of 17th century. Early Microscopes were of two types; Simple Microscope, with a single lens of very short focal length and Compound Microscope, with two double convex lens system including ocular and objective lens with higher magnifying power. Most of the epoch making original discoveries about microorganisms was all made using simple and compound microscopes. Characteristics of microorganisms 1. Their size is very small. 2. There is no cellular differentiation. They are unicellular and one cell is capable of performing all the functions. Some microorganisms are multicellular with little or no cellular differentiation. 3. Microorganisms are present everywhere on the bodies of animals and humans, on plant surfaces, in the air, water, dust, soil, and even inside the intestinal canal of all insects, birds, animals and human beings. Taxonomic Groups Microorganisms have wide taxonomic distribution and include organisms such as protozoa, algae, fungi, bacteria and virus.The schematic illustrations of different microorganisms are shown in Figure S.1. Protozoa are unicellular eukaryotic organisms, motile having cilia, flagella and pseudopodia, saprophytic or parasitic. They are generally present in soil, water and marshy places and their size varies from 5-200 µm. They are animal-like in that they ingest particulate food, lack a rigid cell wall, do not contain chlorophyll. The study of protozoa is known as protozoalogy. They are differentiated on the basis of morphological, nutritional and physiological characteristics. Their role in nature is varied, but the best known protozoa are the few that cause disease in human beings and animals, such as malaria in humans. Some protozoa are beneficial, such as those found in stomach of cattle, sheep and termites that help digest food. Algae are relatively simple organisms, their size varies from 1 µm to several feet. They are considered plant-like because they contain the green pigment chlorophyll, carry out photosynthesis, and have rigid cell walls. They are unicellular to multicellular and either motile or nonmotile. The study of algae is known as Algology or Phycology. These organisms are autotrophic and are found most commonly in aquatic environments or in damp soil. They cause problems by clogging water pipes, releasing toxic chemicals into water bodies, or growing in 2 swimming pools. But extracts of some species have commercial uses: as emulsifiers for foods such as ice-creams; as a source of agar used as solidifying agent in microbial medias and as anti- inflammatory drugs for ulcer treatment. A B CD E F G H I J Figure S. 1. Schemetic illustrations of different microorganisms. [A] Bacillus cereus, [B] Staphylococcus aureus, [C] Saccharomyces cerevisiae, [D] E.coli, [E] Listeria monocytogenes, [F] Red algae, [G] Blue green algae Oscillatoria, [H] Amoeba, [I] Hepatitis virus, [J] Euglena 3 Fungi are either saprophytes or parasites. They have eukaryotic cell structure which, like algae, have rigid cell walls. They form characteristic hyphae called mycelium which may be septate, nonseptate or coenocytic. They form fruiting structures called conidia or exospores and endospores. Spores of fungi are always present in air, dust and soil. Multicellular fungi are also called molds while yeast is an important unicellular fungus. Size range of molds is 2.0-10 µm and yeast has size varying in the range of 5-10 µm. Molds have considerable value; they are used to produce antibiotics- penicillin, cephalosporin etc, fermented products like soy sauce, tempeh, miso, Roquefort and Camembert cheeses, and many other products. But they are also implicated in various human, animal and plant diseases including athlete’s foot and the moldy spoilage of grains and peanuts. The unicellular yeasts are widely used in Baking industry and for the production of all alcoholic beverages like wine, beer etc. On the other hand, some yeasts cause food spoilage and diseases such as vaginitis and thrush (an oral infection). Bacteria are unicellular microorganisms. Their size varies from 1-5 µm and have rod, coccus or spiral shape. They have prokaryotic cellular organization and cell division is usually by binary fission. Some bacteria having mycelial morphology are known as Actinomycetes and are very important in production of antibiotics. Bacteria are important in agriculture and play important role in cycle of biological nitrogen fixation. With respect to food, they are important in fermentations, food spoilage, food poisoning and food preservation. The wide range of industrial products derived from bacteria affect the human society in numerous ways. Their activities are of enormous importance and some are beneficial while others are harmful. The study of bacteria is known as Bacteriology. Viruses are ultra-microscopic, noncellular obligate parasites of plants, animals and bacteria as well as other protists. Their size varies from 0.015µm -0.2 µm and shapes from spherical, rod, flexuous to cozohedral. They can be seen only under an electron microscope. Unlike cells, viruses contain only one type of nucleic acid, either DNA or RNA, which is surrounded by a protein-coat. They lack the cellular components necessary for metabolism or independent reproduction, viruses can mutiply only on living cells. The study of viruses is known as virology. Viruses cause large number of diseases in humans (such as AIDS, common cold, poliomyelitis, SARS, genital herpes, hepatitis etc), plants (tobacco mosaic disease, papaya ring spot disease etc) and foot-and-mouth disease of animals. In addition, some retroviruses have also been implicated in the growth of some malignant tumors. Historical Developments in Microbiology Some momentous discoveries in science were made by amateurs, rather than by professional scientists. One of such major stalwarts in the history of microbiology a natural scientist, owned his own dry goods store, and was also the official wine taster for the city of Delft in Holland. Antony van Leeuwenhoek (1632 -1723; Figure S.2A) known as the Father of Microbiology, was a pioneer in the field of Microscopy and used microscopes of his own design and manufacture. He was a linen merchant who built microscopes as a hobby, had little formal education and knew only Dutch language. He made about 500 optical lenses that could magnify objects 275 times and was an amazing feat. He enjoyed using his microscopes to look at the various things including river water, pepper infusions, saliva feces and more. He communicated his findings to the Royal Society of London in the form of long series of letters which were translated and published in the Proceedings of Royal Society. 4 Leeuwenhoek constructed many microscopes with a single lens which consisted of a spherical lens mounted between two small metal sheets of silver or brass (Figure S.2B). The specimen was placed on the point of a blunt pin and brought into focus by manipulating two perpendicular and a linear screws. Leeuwenhoek’s Findings Leeuwenhoek had unusual degree of curiosity and observed every object that could be seen through his microscope. He was one of the greatest Innovators driven by curiosity and infinite energy. In his letter of September 17, 1683 with his drawings about ‘animals’ in the scrapings of teeth he described different types of bacteria and called them ‘animalcules’ (Figure S.2C). He also made magnificent observations on the microscopic structure of seeds and embryos of plants and some invertebrate animals. He discovered Spermatozoa, RBC and is therefore known as Father of Animal Histology. He described characteristic microflora of human mouth, curd, vinegar and infact discovered all the different types of microorganisms known today including protozoa, algae, yeast and bacteria. He also emphasized the abundance of these microorganisms besides their great diversity. Figure S.2 [A] Antony Von Leeuwenhoek. [B] The Leeuwenhoek’s microscope. [C] Leeuwenhoek’s sketches of bacteria from the human mouth. He was elected a fellow of the Royal Society of London (FRS) in 1680.The Royal Netherland Academy of Arts and Science established a ‘Leeuwenhoek Medal’ in his honor in 1877. The ‘Antony van Leeuwenhoek chair’ established in Delft places a strong emphasis on research and appointments are made on the basis of achievements. 5 Origin of Leeuwenhoek’s microorganisms Soon after the discovery of microorganisms by Leeuwenhoek, scientists began to study the origin of these small organisms from the point of view of the two schools of thought; One believed in the Theory of Abiogenesis or the concept of spontaneous generation i.e.