Fundamentals of Microbiology
Unit –I
History and scope
Definition
Microorganisms, or microbes, are very small organisms; many types of microbes are too small to see without a microscope, although some parasites and fungi are visible to the naked eye.
Microbiology often has been defined as the study of organisms and agents too small to be seen clearly by the unaided eye—that is, the study of microorganisms.
Microorganisms differ from each other not only in size, but also in structure, habitat, metabolism, and many other characteristics.
Microorganisms are found in each of the three domains of life: Archaea, Bacteria, and Eukarya. Microbes within the domains Bacteria and Archaea are all prokaryotes (their cells lack a nucleus), whereas microbes in the domain Eukarya are eukaryotes (their cells have a nucleus). Some microorganisms, such as viruses, do not fall within any of the three domains of life.
Prokaryotes
Bacteria
Bacteria are prokaryotes that are usually single-celled organisms because their genetic material (DNA) is not housed within a true nucleus. Most have cell walls that contain the structural molecule peptidoglycan. Bacteria are often described in terms of their general shape. Common shapes include spherical (coccus), rod-shaped (bacillus), or curved (spirillum, spirochete, or vibrio).
They have a wide range of metabolic capabilities and can grow in a variety of environments, using different combinations of nutrients. Some bacteria are photosynthetic, such as oxygenic cyanobacteria and anoxygenic green sulfur and green nonsulfur bacteria; these bacteria use energy derived from sunlight and fix carbon dioxide for growth. Other types of bacteria are nonphotosynthetic, obtaining their energy from organic or inorganic compounds in their environment.
They are abundant in soil, water, and air and are also major inhabitants of our skin, mouth, and intestines. Some bacteria live in environments that have extreme temperatures, pH, or salinity.
Archaea
Archaea are procaryotes that are distinguished from bacteria by many features, most notably their unique ribosomal RNA sequences. They also lack peptidoglycan in their cell walls and have unique membrane lipids. Some have unusual metabolic characteristics, such as the methanogens, which generate methane gas. Many archaea are found in extreme environments like very cold, very hot, very basic, or very acidic. Pathogenic archaea have not yet been identified.
Eukaryotic Microorganisms
The domain Eukarya contains all eukaryotes, including uni- or multicellular eukaryotes such as protists, fungi, plants, and animals. The major defining characteristic of eukaryotes is that their cells contain a nucleus.
Protists
Protists are unicellular eukaryotes that are not plants, animals, or fungi. Algae and protozoa are examples of protists.
Algae
Algae are photosynthetic protists that together with the cyanobacteria produce about 75% of the planet’s oxygen. Their cells are surrounded by cell walls made of cellulose, a type of carbohydrate. They are also the foundation of aquatic food chains.
Many consumer products contain ingredients derived from algae, such as carrageenan or alginic acid, which are found in some brands of ice cream, salad dressing, beverages, lipstick, and toothpaste. A derivative of algae also plays a prominent role in the microbiology laboratory. Agar, a gel derived from algae, can be mixed with various nutrients and used to grow microorganisms in a Petri dish. Algae are also being developed as a possible source of biofuels.
Protozoa
Protozoa are unicellular, animal-like protists that are usually motile. Some protozoa move with help from hair-like structures called cilia or whip-like structures called flagella. Others extend part of their cell membrane and cytoplasm to propel themselves forward. These cytoplasmic extensions are called pseudopods (“false feet”). Many free-living protozoa function as the principal hunters and grazers of the microbial world. They obtain nutrients by ingesting organic matter and other microbes. They can be found in many different environments and some are normal inhabitants of the intestinal tracts of animals, where they aid in the digestion of complex materials such as cellulose. Most protozoa are harmless, but some are pathogens that can cause disease in animals or humans.
Slime molds are protists that are like protozoa in one stage of their life cycle but are like fungi in another. In the protozoan phase, they hunt for and engulf food particles, consuming decaying vegetation and other microbes.
Water molds, as their name implies, are found in the surface water of freshwater sources and moist soil. They feed on decaying vegetation such as logs and mulch. Some water molds have produced devastating plant infections, including the Great Potato Famine of 1846–1847.
Fungi
Fungi (singular: fungus) are also eukaryotes. Some multicellular fungi, such as mushrooms, resemble plants, but they are actually quite different. Fungi are not photosynthetic, and their cell walls are usually made out of chitin rather than cellulose. Molds and mushrooms are multicellular fungi that form thin, threadlike structures called hyphae. They absorb nutrients from their environment, including the organic molecules that they use as a source of carbon and energy.
Unicellular fungi—yeasts—are included within the study of microbiology. There are more than 1000 known species. Yeasts are found in many different environments, from the deep sea to the human navel. Some yeasts have beneficial uses, such as causing bread to rise and beverages to ferment, producing antibiotics, and decomposing dead organisms. Yeasts can also cause food to spoil. Some even cause diseases, such as vaginal yeast infections and oral thrush.
Molds are made up of long filaments that form visible colonies. Molds are found in many different environments, from soil to rotting food to dank bathroom corners. Molds have been used to make pharmaceuticals, including penicillin, which is one of the most commonly prescribed antibiotics, and cyclosporine used to prevent organ rejection following a transplant.
Viruses
Viruses are acellular microorganisms, which means they are not composed of cells. Essentially, a virus consists of proteins and genetic material—either DNA or RNA, but never both—that are inert outside of a host organism. However, by incorporating themselves into a host cell, viruses are able to co-opt the host’s cellular mechanisms to multiply and infect other hosts. They are the smallest of all microbes (the smallest is 10,000 times smaller than a typical bacterium),
Viruses can infect all types of cells, from human cells to the cells of other microorganisms. In humans, viruses are responsible for numerous diseases, include smallpox, rabies, influenza, AIDS, common cold, and some cancers. However, many viruses do not cause disease.
Microbiology as a Field of Study
Microbiology is a broad term that encompasses the study of all different types of microorganisms. But in practice, microbiologists tend to specialize in one of several subfields. For example,
Bacteriology is the study of bacteria
Mycology is the study of fungi;
Protozoology is the study of protozoa;
Parasitology is the study of helminths and other parasites;
Virology is the study of viruses, and
Immunology, the study of the immune system.
History of Microbiology
The revolution of microbiology are categorized into four groups such as the Discovery era, Transition era, Golden era and Modern era
Discovery era (Contribution of Antonie van Leeuwenhoek. 1632–1723)
Antonie van Leeuwenhoek, sometimes hailed as “the Father of Microbiology,” is typically credited as the first person to have created microscopes powerful enough to view microbes. Born in the city of Delft in the Dutch Republic, van Leeuwenhoek began his career selling fabrics. However, he later became interested in lens making (perhaps to look at threads) and his innovative techniques produced microscopes that allowed him to observe microorganisms as no one had before. In 1674, he described his observations of single-celled organisms (Little animalcules), whose existence was previously unknown, in a series of letters to the Royal Society of London. His report was initially met with skepticism, but his claims were soon verified and he became something of a celebrity in the scientific community.
1. He first discovered & reported bacteria (1676).
2. Observed Microscopic structure of seeds & embryos of plants & some invertebrates.
3. He discovered Spermatozoa & RBCs.
4. He discovered characteristic microbes of the human mouth, curd, vinegar.
5. Emphasized the abundance of these microorganisms.
The scientific community acknowledged him as the father of protozoology and bacteriology.
Transition era
The Theory of Spontaneous Generation (Abiogenesis)
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 nonliving matter. Aristotle proposed that life arose from nonliving material if the material contained pneuma (“vital heat”).
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 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 preexisting 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 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.
Disproving Spontaneous Generation
Theodore Schwann (1810–1882) allowed air to enter a flask containing a sterile nutrient solution after the air had passed through a red-hot tube. The flask remained sterile.
Georg Friedrich Schroder and Theodor von Dusch allowed air to enter a flask of heat-sterilized medium after it had passed through sterile cotton wool. No growth occurred in the medium even though the air had not been heated.
Louis Pasteur (1822-1895), a prominent French chemist who had been studying microbial fermentation and the causes of wine spoilage, accepted the challenge and would ultimately win both the debate and the Academy’s prize. 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.
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.
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| Disproving Abiogenesis theory (Swan Neck Experiment) |
Modern era
Contribution of John Tyndall
John Tyndall(1820-1893), an English physicist,was able to explain satisfactorily the need for prolonged heating to eliminate microbial life from infusions. He concluded, by exposing infusions to heat for varying times, that bacteria existed in two forms-a heat stable form and a heat-sensitive form. It required either prolonged or intermittent heating to destroy heat-stable forms. Intermittent heating, now called tyndallization, killed both forms since between periods of heat treatment the heat-stable forms changed to heat-sensitive forms.
Contribution of Louis Pasteur
Louis Pasteur (1822-1895) was born in the village of Dole, France on December 27, 1822 the son of humble parents. His father was a tanner. He was originally trained as a chemist, but his studies on fermentation led him to take interest in microorganisms. His discoveries revolutionized medical practice, although he never studied medicine.
1 .The term microbiology, as the study of living organisms of microscopic size, was coined by Pasteur.
2. He also coined the term vaccine.
3. He use various forms of nutrient fluid to grow microorganisms and showed that a medium suitable for one might be unsuitable for another ,so for successful cultivation it was necessary to discover a suitable growth medium and to establish optimal conditions of temperature, acidity or alkalinity, and oxygen tension.
4. He showed that some organisms were not destroyed by boiling. For the sterilization of fluids he advocated heating to 120oC under pressure and for glassware the use of dry heat at 1700C.He showed that cotton plugs (a primitive air-filtration device) could prevent microbes from reaching otherwise air-exposed sterile broths.
5. In 1860-1861, he disapproved the theory of spontaneous generation .In a series of classic experiments, Pasteur proved conclusively that all forms of life, even microbes, arose only from their alike and not de novo.
6. In 1860-1864, he gave experimental evidence that fermentation and putrefaction are effects of microbial growth.
7. In 1863-1865, he devised the process of destroying bacteria, known as pasteurization. He proved that the 'disease of wine' could be prevented without altering the flavor by heating the wine for a short time to a temperature (55-60oC), a little more than halfway between its freezing and boiling points. This process (pasteurization) is employed throughout the civilized world today to preserve milk and certain other perishable foods.
8. In 1865, he was asked to attempt to find the cause of pebrine, a disease which was threatening to ruin the business of raising silkworms, an important industry in Southern France. Pasteur succeeded in demonstrating that this silkworm disease was caused by microscopic germs, protozoa, and showed that the infection could be eliminated by choosing for breeding only those worms which were free of the parasites. This discovery was one more step towards the establishment of the truth of the germ theory of disease.
9. In 1877, Koch and Pasteur demonstrated that anthrax is caused by bacteria. Pasteur grew the organisms in sterilized yeast water and kept them in the laboratory for several months, transferring them frequently to new culture fluid, in which they multiplied readily, and showed that these cultures would always cause anthrax when inoculated into healthy animals.
10. In 1880, he prevented chicken cholera by injection of live attenuated culture. He found that pure cultures of the germ of this disease which had been kept in the laboratory for some time would not kill his animals as fresh cultures did, but would merely cause a passing illness from which the chickens recovered. Then he discovered that the animals that had recovered from a previous inoculation of weakened germs were immune, and did not succumb to the disease. Pasteur immediately perceived that it might be possible to make individuals resistant by inoculating them with the weakened (and therefore harmless) germs of a particular disease.
11. In 1880, he first cultured staphylococci in liquid medium and produced abscesses by inoculating them into rabbits.
12. In 1881, he developed live attenuated anthrax vaccine.
13. In 1881, pneumococci were first noticed by Pasteur and Sternberg independently.
14. The crowning achievement of Pasteur was the successful application of the principle of vaccination to the prevention of rabies, or hydrophobia, in human beings and developed Pasteur rabies vaccine in 1885. He did not find the germs of this disease under his microscope (now known as rabies virus) but he was able to propagate them by artificial inoculation into the brains of dogs and rabbits. Finally he developed a system of vaccination with weakened virus which prevented the development of this fatal disease if the inoculations are given soon after the bite of the rabid animal. He gave the first treatment for rabies in 1885 to a rabid dog.
15. In 1887, Pasteur and Joubert first described Clostridium septicum and called it Vibrion septique.
In 1888, in recognition of his incomparable achievement, Pasteur Institute of Paris was built by public contribution during his lifetime for investigations off infectious disease and preparation of vaccines. Acclaimed the world over for his epoch making discoveries, Pasteur Institute of Paris September 28, 1895. His body lies in Pasteur Institute of Paris. Today the Pasteur Institute is a thriving research centre to appropriate memorial to its founder.
Contribution of Robert Koch
A bacteriologist second only to Louis Pasteur was Robert Koch (1843-1910). He was born on December 11, 1843 in Germany. In 1866, he took his degree in Medicine and began a general practice in a small country town. In 1872, he took a diploma in public health. He became interested in microscopical studies. With a microscope given as a birthday present by his wife he set up a primitive laboratory and started his studies on microbes in relation to diseases. His contributions to microbiology are variegated and enormous:
1. In 187, Robert Koch reported the isolation of anthrax bacillus in pure culture, formation and germination of its spores and the proof of its infectiousness. This agent as the sole cause of anthrax was confirmed by Pasteur.
2. In 1877, he introduced the method of making of smears of bacteria on glass slides, and of staining them with the aniline dyes. He was also the first to employ in bacteriology work the improved compound microscope of Abbe.
3. In 1878, his studies of wound infections explored the role of animal experimentation in establishing the cause of bacterial infections.
4. In 1881, he described means of cultivating bacteria on solid media, thus making it possible to obtain pure cultures by transferring material from a single colony. First he used as his growth medium pieces of potato, then 2.5-5.0% gelatin to prepare solid media fortifying them with 1% meat extract as an essential ingredient. He poured melted nutrient gelatin on glass slides and allowed them to set under a bell jar to prevent contamination. He inoculated media using sterile needles or platinum wires dipped in suspensions to take minimum inoculum and lightly drawing lines across the medium. He also developed pour plate method. At the suggestion of Anglina Hesse, the American wife of his assistant, he substituted agar in place of gelatin as solidifying agent for the media. She had used it to solidify broths in her kitchen.
5. The hanging-drop method of studying bacteria as used today is a product of his genius.
6. In1882, Koch startled the world by announcing his discovery of tubercle bacillus (Mycobacterium tuberculosis), the causative agent of tuberculosis. He described a special staining method for detection of this organism and grew it in pure cultures in the laboratory. He showed that animals would develop tuberculosis when inoculated with pure cultures of this organisms from the diseased tissues of the animals. The discovery of the tubercle bacillus was called Koch’s bacillus and tuberculosis, Koch’s disease.
7. In 1883, he discovered the causative agents of cholera (Vibrio cholerae), Egyptian ophthalmia (pink eye) and Koch Weeks bacillus.
8. In 1884, Koch expounded the postulates or laws by which an organism may be proved to be the cause of a particular disease. These are known as Koch’s postulates.
9. Koch continued his work on tuberculosis and in 1890-1891 he showed how a normal guinea-pig and an already infected guinea-pig behaved differently to an infection with tubercle bacillus. This is known as Koch’s phenomenon.
10. From 1885-1890, Koch studied various organisms present in water, soil and air and their relation in prevention of disease.
11. He invented the hot air oven and steam sterilizer, basic tools in any microbiology laboratory. He developed methods for testing antiseptics and to distinguish between bacteriostatic and bactericidal concentrations.
He became the first director of the Koch Institute for infectious diseases which was opened in 1891. He attracted many pupils from all over the world. His pupils include famous bacteriology such as Graffky (discoverer of typhoid bacillus), Loeffler (discoverer of diptheria bacillus), von Behring (discoverer of diphtheria bacillus), Pfeiffer (described Pfeiffer’s bacillus and phenomenon), Kitasato (discoverer of plague bacillus), welch (discoverer of gas gangrene bacillus), Ehrlich and Wasserman.
In 1905, he was awarded the Noble prize in Medicine for his work on tuberculosis. Together with Louis Pasteur, he laid the foundations of modern bacteriology.
Contribution of Antonie Van Leeuwenhoek
Antonie Van Leeuwenhoek (pronounced Layu-wen-hook) (132-1723), a citizen of Delft, Holland, was not a man of great learning, but he was very ingenious. He became expert in the grinding of simple magnifying lenses. He made these lenses of small bits of glass, polished them very carefully, and mounted each separately between two brass, copper, silver, or gold plates, to which he fastened an adjustable holder for the object to be examined. He constructed many of these ‘microscopes’ each containing a single lens ground by himself. The best of lenses magnified about 200 times. His microscopes were superior to any of that time, He observed, drew and measured a large number of living organism including bacteria and protozoa in materials such as rain water, pond and well water, and saliva and the intestinal contents of healthy subjects and communicated them to the Royal society of London in 1683. He was the first to accurately describe different shapes of bacteria (coccal, bacillary and spiral) and picture their arrangement in infected material.
Leeuwenhoek observed that very large numbers of bacteria appeared in watery infusions of animals or vegetable matter which were left to stand for a week or two at room temperature. He believed that these huge populations were the progeny of a few parental organisms, or seeds that were originally present in the materials of the infusion or had entered it from the air. The significance of these observations was not realized then and to Leeuwenhoek the world of ‘little animalcules’ represented only a curiosity of nature. Their importance in medicine and other areas ofbiology came to be recognized two centuries later.
Contribution of Edward Jenner
Edward Jenner (1749-1823) was born in Berkeley in 1749. Orphaned before he was 5-years-old, his brothers and sisters set him on a career of medicine. He completed his training with the great surgeon John Hunter in London. He introduced the modern method of vaccination to prevent smallpox. He observed that milkmaids who contracted cowpox or vaccinia while milking were sub-sequently immune to smallpox. On May 14, 179, he devised a brave experiment. He performed a vaccination against smallpox by transferring material from a cowpox pustule on the hand of a milkmaid, Sarah Nelmes, to the arm of a small boy named James Phipps, his gardener’s son. He failed to develop the disease. By 1798 Jenner published his results in 23 cases and by 1800 about 6000 persons had been inoculated with cowpox to prevent smallpox. The terms vaccine and vaccination were first used by Pasteur out of deference to Jenner.
In 1967 the World Health Organisation masterminded a final global plan to eradicate smallpox. Success was announced in 1980 with the declaration: Smallpox is dead. Thanks for Jenner. Edward Jenner’s discovery has now been developed into one of the most important parts of modern medicine-Immunology. This science helps us to treat many infectious diseases, and to understand transplantation, allergies and diseases such as rheumatoid arthritis and AIDS.
Koch's Postulates
Four criteria that were established by Robert Koch to identify the causative agent of a particular disease, these include:
- The microorganism or other pathogen must be present in all cases of the disease.
- The pathogen can be isolated from the diseased host and grown in pure culture.
- The pathogen from the pure culture must cause the disease when inoculated into a healthy, susceptible laboratory animal.
- The pathogen must be reisolated from the new host and shown to be the same as the originally inoculated pathogen
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Scope of Microbiology
The late scientist-writer Steven Jay Gould emphasized, we live in the Age of Bacteria. They were the first living organisms on our planet and live virtually everywhere life is possible. Furthermore, the whole biosphere depends on their activities, and they influence human society in countless ways. Because microorganisms play such diverse roles, modern microbiology is a large discipline with many different specialties; it has a great impact on fields such as medicine, agricultural and food sciences, ecology, genetics, biochemistry, and molecular biology. One indication of the importance of microbiology is the Nobel Prize given for work in physiology or medicine.
Microbiology has both basic and applied aspects. The basic aspects are concerned with the biology of microorganisms themselves and include such fields as bacteriology, virology, mycology (study of fungi), phycology or algology (study of algae), protozoology, microbial cytology and physiology, microbial genetics and molecular biology, microbial ecology, and microbial taxonomy. The applied aspects are concerned with practical problems such as disease, water and wastewater treatment, food spoilage and food production, and industrial uses of microbes.
A discussion of some of the major fields of microbiology and the occupations they provide follows.
Medical microbiology
One of the most active and important fields in microbiology is medical microbiology, which deals with diseases of humans and animals. Medical microbiologists identify the agents causing infectious diseases and plan measures for their control and elimination. Frequently they are involved in tracking down new, unidentified pathogens such as the agent that causes variant Creutzfeldt-Jakob disease, (the human version of “mad cow disease”) the hantavirus, the West Nile virus, and the virus responsible for SARS. These microbiologists also study the ways in which microorganisms cause disease.
Public health microbiology
Public health microbiology is closely related to medical microbiology. Public health microbiologists try to identify and control the spread of communicable diseases. They often monitor community food establishments and water supplies in an attempt to keep them safe and free from infectious disease agents.
Immunology
Immunology is concerned with how the immune system protects the body from pathogens and the response of infectious agents. It is one of the fastest growing areas in science; for example, techniques for the production and use of monoclonal antibodies have developed extremely rapidly. Immunology also deals with practical health problems such as the nature and treatment of allergies and autoimmune diseases like rheumatoid arthritis.
Agricultural microbiology
Agricultural microbiology is concerned with the impact of microorganisms on agriculture. Agricultural microbiologists try to combat plant diseases that attack important food crops, work on methods to increase soil fertility and crop yields, and study the role of microorganisms living in the digestive tracts of ruminants such as cattle. Currently there is great interest in using bacterial and viral insect pathogens as substitutes for chemical pesticides.
Microbial ecology
Microbial ecology is concerned with the relationships between microorganisms and the components of their living and non-living habitats. Microbial ecologists study the global and local contributions of microorganisms to the carbon, nitrogen, and sulphur cycles. The study of pollution effects on microorganisms also is important because of the impact these organisms have on the environment. Microbial ecologists are employing microorganisms in bioremediation to reduce pollution.
Food and dairy microbiology
Food and dairy microbiology is concerned with the microbial spoilage of food and the transmission of foodborne diseases such as botulism and salmonellosis. The researchers are use microorganisms to make foods such as cheeses, yogurts, pickles, and beer. In the future, microorganisms themselves may become a more important nutrient source for livestock and humans.
Industrial microbiology
Industrial microbiology is concerned with the use microorganisms to make products such as antibiotics, vaccines, steroids, alcohols and other solvents, vitamins, amino acids, and enzymes. In 1929, Alexander Fleming discovered that the fungus Penicillium produced what he called penicillin, the first antibiotic that could successfully control bacterial infections. Industrial microbiologists identify microbes of use to industry. They also engineer microbes with desirable traits and devise systems for culturing them and isolating the products they make.
Microbial physiology
Microbial physiology is concerned with studying the synthesis of antibiotics and toxins, microbial energy production, the ways in which microorganisms survive harsh environmental conditions, microbial nitrogen fixation, and the effects of chemical and physical agents on microbial growth and survival.
Microbial genetics and molecular biology
Microbial genetics and molecular biology focus on the nature of genetic information and how it regulates the development and function of cells and organisms. The use of microorganisms has been very helpful in understanding gene structure and function. Microbial geneticists play an important role in applied microbiology because they develop techniques that are useful in agricultural microbiology, industrial microbiology, food and dairy microbiology, and medicine.
Source: Microbiology – Open staxTM
Microbiology – Prescott, Harley and Klein’s -7th edition
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