history of microbiology

HISTORY OF MICROBIOLOGY


Microorganisms were probably the first living things to appear on earth and the study of fossil remains indicate that microbial infections and epidemic diseases existed thousands of years ago.

• It was Rogen Bacon who in the 13 century postulated that disease is produced by invisible living creatures.

• Physician Girolamo Fracastoro of North Italy made this suggestion again in 1546. Fracastoro wrote a treatise De Contagione in which he said disease was caused by minute “seed” or “germ” and was spread from person to person.

• In 1665, Robert Hooke used a simple lens that magnified objects approx. 30X. He examined thin slices of cork, the bark of oak tree and found that cork was made of tiny boxes that Hooke referred to as cell.

• It was followed by Matthias Schleiden and Theodore Scwann who examined a variety of micro organisms and in 1838- 1839 reported that “all forms of life are composed of cells.” an observation that later became cell theory. The cell theory has since been modified to all life is composed of cells that originate from other cells.


THE DISCOVERY OF MICROBIOLOGY AS A DISCIPLINE COULD BE TRACED ALONG THE FOLLOWING HISTORICAL ERAS:

• Discovery Era
- Antony van Leeuwenhoek
- Robert Hooke

• Transition Era
- Francesco Redi
- John Needham
- Lazzaro Spallanzani
- Schulze and Scwann
- Schroeder and Von Dusch

• Golden Era
- Louis Pasteur
- Robert Koch

• Immuniztion Era
- Edward Jenner
- Lord joseph lister
- Elie metchnikoff

• Chemotherapy Era
- Alexender fleming

• Molecular Era
- Joshua lederberg
- Winogradsky and beijerenck




DISCOERY ERA-

This period concerns with the discovery of microbial world that has been dominated by Antony van Leeuwenhoek




1. Antony van Leeuwenhoek [1632- 1723]

Leeuwenhoek was born in Holland (Netherlands) delft on October 24, 1632. It was a cloth merchant only who discovered bacteria, free living and parasitic microscopic protists, sperm cells, blood cells, microscopic nematode, and rotifers and much more.

His notable contributions to microbiology are:

• Discovery of microbial world- He was the first to report his observations with accurate descriptions and drawings. It was he only who described microorganisms accurately for very first time. He described thread like fungi as well as certain microscopic algae. He gave outlined structural details of familiar Paramecium and amoeba.

• Introduction of term animalcules- In 1676 he gave the term animalcules to microorganisms. His descriptions of protozoa were so accurate that many of the forms he described were easily recognized today.

• Formation of microscopes- He was a Dutch linen merchant but spent much of his time constructing simple microscopes composed of double convex lenses held between two silver plates. He constructed over 250 powerful microscopes that could magnify around 50 to 300 times and he may have illuminated his liquid specimens by placing them between two pieces of glass and shining light on them at an angle of 45° to specimen plane. This arrangement would have provided a form of dark field illumination and made microbes clearly visible

• Contribution to medicines- He contributed to medicines also. He was founder of animal histology. He discovered the existence of spermatozoa and red blood cells. He discovered and described the capillary circulation and completed the work on circulation of blood, the capillary connection between arteries and veins.

• Transmission of letters to Royal Society- He transmitted his observations to the royal society in 1676 in the form of long series of letters written in Dutch including numerous drawings. He astonished everything by claming that many oh the tiny things he saw with his lens alive because he saw them swimming in purposefully about. Most of these letters were translated and published in England in the proceedings of Royal Society. He got fellowship in 1680 from Royal Society.

Because of this extraordinary contribution to microbiology, he is considered as Father of Bacteriology and Protozoology.




2. Robert Hooke [1635- 1703]

Born on July 18, 1635 at freshwater on Isle of Wight. He was apparently largely educated at home by his father he was able to enter Westminster school and from there went to Oxford where some of the best scientists of England were working. Hooke impressed other scientists with his skills at designing experiments and building equipments.

In 1662, Hooke was named curator of experiments of the newly formed Royal Society of London meaning that he was responsible for demonstrating new experiments. He was an active, infatigable genius even almost to last. He died in London on March 3, 1703.

His notable contributions to microbiology are:

• Micrographia- Hooke’s reputation in history of biology largely rests on his book Micrographia published in 1665. He devised compound microscope and illumination system.

• Study of cell- In 1665, he used a simple lens that magnified objects approx. 30x he examined thin slices of cork, the bark of oak tree and found that cork was made of tiny boxes that Hooke referred to as cell. He discovered plant cell.



TRANSITION ERA-

During this period, noteworthy contribution was made: the controversy over spontaneous generation that said that living organisms could develop from non living matter i.e. abiogenesis.

• Francesco Redi- The ancient belief in spontaneous generation was first of all challenged by Redi, who carried out a series of experiments on decaying meat and its ability to produce maggots spontaneously. Redi in 1665 put the theory of spontaneous generation to rest by conducting a simple experiment in which he placed meats in three jars. One jar was covered with a fine gauze, second was covered with paper and third was left uncovered. Flies entered the jar that was open to air i.e. left uncovered and landed on meat where they laid their eggs that later developed into maggots. The other two pieces of meat did not produce maggots spontaneously. However, flies were attracted to the gauze covered jars and laid their eggs on the gauze and maggots subsequently developed access to the meat, indicating that maggots were the offspring of the flies and did not arise from some “vital source” in the meat as previously believed.

• John Needham- he was probably the greatest supporter of the theory of spontaneous generation. In 1749, he proposed that tiny organisms, the animalcules arose spontaneously on his mutton gravy. He had covered the flasks with cork as done by Redi and even heated some flasks. Still the microbes appeared on mutton broth.

• Lazzaro Spallanzani- Spallanzani attempted to refuse Needham’s work by performing extensive experiments. He boiled beef broth for longer period, removed the air from the flask and then sealed the container. Following incubation, no growth was observed in flasks. When he was accused of destroying the vegetative force of the nutrients by over heating, he showed that the heated nutrients could still grow animalcules when exposed to air by simply making a small crack in the neck. Thus, in Spallanzani in 1775 disproved the doctrine of spontaneous generation.

• Franze Schulze and Theodor Scwann- Needham and other critics countered the doctrine of Spallanzani and stated that life force had been killed when the flasks were from oxygen, a gas known to be required in the respiration of animals. Schulze and Scwann, who were of the view that air was the source of microbes and sought to prove this by passing air through hot glass tubes or strong chemicals into boiled infusions into flasks, answered this argument. The infusion in both the cases remained free from the microbes. However, the die hard advocates of spontaneous generation were still not convinced and said that the treatment of air by acid or heat had altered the air so that it would not support growth.

• Georg Schroeder and Theodor Von Dusch- In 1854, Schroeder and Von Dusch performed convincing experiments to disprove the theory of spontaneous generation by simply passing air through cotton into flasks containing heated broth. No growth of microbes was observed on the infusions due to the filtering out of microscopic organisms by cotton. Thus, Schroeder and Von Dusch were the first to introduce the idea of using cotton plugs for plugging microbial culture tubes in 1854.




GOLDEN AGE OF MICROBIOLOGY-

Golden age of microbiology began with the work of Louis Pasteur of France and Robert Koch of Germany who had their own research institutes. Here we find indisputable proof that microbes cause disease. More important, there was an acceptance of their work by the scientific community throughout the world and a willingness to continue and expand their work. During the period, we see the real beginning of microbiology as a discipline of biology.






3. Louis Pasteur [1822-1895]:

Pasteur was born on December 27,1822 in Dole, France. His name is forever cemented in history of medicines. From his young years, Pasteur was a talented artist, his portraits were so professional, that his name was listed in the compendiums of artists in xix century.

His notable contributions to microbiology are:

• Microbes as cause of disease- Pasteur in 1842, demonstrated that microbes could be cause of disease for if they could spoil the wine; perhaps they could also make the body sick. This leads to the development of germ theory of diseases.

• Crystallography – He studied the shapes of organic crystals and proved that they have two kinds of structure, later called isomers and formulated the law: asymmetry differentiates the organic world from mineral world. The external shape of crystal, its molecular composition and its action on polarized light are all linked. Polarized light is rotated by asymmetric crystals, not by crystals that have plane of symmetry.

• Alcoholic fermentation (1857)- Fermentation is a biological phenomenon. Each type of wine fermentation is caused by a specific microorganism, which can be cultivated. Also Pasteur found that the main cause of economic losses in France wine industry, recommended the correct type of micro organism to be used in winery (1864) and recommended to heat the wine up to 55°C killing the unwanted bacteria (process known as Pasteurization).

• Pasteur against spontaneous generation (1860)- Pasteur performed a series of experiments to prove that although micro organisms were present in air they were not spontaneously produced. To prove that air was source of microbes, he filled several round bottomed flask with nutrient solution and fashioned their openings into elongated, swan neck shaped tubes. The flask’s openings were freely open to air but curved so that gravity would cause any air borne dust particles to deposit in lower part of neck. The flask were heated to sterilize the broth and incubated. No growth occurred even though the contents of flasks were exposed to air. Pasteur pointed out that no growth took place because dust and germs had been trapped on the walls of the curved necks but if the necks were broken off so that dust fell directly down into flask, microbial growth commenced immediately. Some of the ingenious flasks are still on display at Pasteur Institute in Paris in their original sterile form. This experiment clearly showed that micro organisms present in or on non living material such as dust or water were responsible for the contamination of sterile solutions. PASTEUR thus in 1861 finally resolved the controversy of spontaneous generation vs biogenesis and proved that micro organisms are not spontaneously generated from inanimate matter but arise from other micro organisms.

• Disease of silk worms (1865-1870)- Healthy worms became infected when allowed to nest on leaves used by infected worms. He also noted that the susceptibility of the worms varied widely, some worms dying shortly after infection, some weeks later, some not at all. Pasteur isolated bacilli of pebrine and flacherie worked out hygienic rules for silkworms’ farmers.

• Pasteurization- Pasteur in 1867 suggested that, mild heating at 62.8°C for 30 minutes, rather than boiling, was enough to destroy the undesirable microorganisms without ruining the taste of product, the process was called Pasteurization. It was introduced in United States on a commercial basis in 1892.

• Germ theory of disease (1877) - The top of Pasteur‘s career were development of the germ theory of disease and the use of vaccines and other physicians antiseptic medicine and surgery.

• Anthrax (1877-1881) - Anthrax is transmitted from animals to humans caused by Bacillus anthracis discovered by Robert Koch in 1876. Pasteur isolated the germs and started-
-vaccinating sheep against anthrax in 1879
-vaccinating chickens against chicken cholera 1879

Discovery of immunization against disease using weakened bacteria.

• Rabies (1885) - The final and certainly most famous success Pasteur research was the development of a vaccine against rabies or hydrophobia on July 6, 1885, 9-year-old Joseph Mister was the first person to be successfully treated against rabies with Pasteur vaccine. After that, people started coming to Pasteur. Ill wolf bit a group of Russian peasants from Smolensk. There was little hope for any success, because 12 days passed after incident but miraculously 16 people from 19 survived due to Pasteur’s help.

• Pasteur’s effect- Pasteur was the first to introduce two terms: aerobic anaerobic. He told that more production of alcohol takes place in anaerobic conditions by anaerobic yeasts. This is called Pasteur’s effect.

Because of his notable contributions to the field of microbiology Pasteur is called as Father of Modern Microbiology and Father of Fermentation Technology.





4. Robert Koch [1843- 1910]

Robert Koch was a German scientist, born in Hanover in 1843. Koch read Louis Pasteur’s work and in 1872 began research in microbes affecting diseased animals and people. He first studied mathematics and natural sciences and then medicines.

• Koch’s postulates- The most notable contribution of Koch was the establishment of casual relationship between a microorganism and a specific disease by applying a set of criteria to as Koch’s postulates or “Standards of Proof.” These were established in 1884 are the milestones of germ theory of disease and are necessary for identifying etiological or specific cause of disease.

These are as follows:

- The suspected microorganism must always be present in diseased but never in healthy individuals.
- The microorganism must be isolated in a pure culture on nutrient medium.
- The same disease must result when the isolated microorganism is inoculated into a healthy host.
- The same microorganism must be re-isolated from the experimentally infected host.

• Experimentation with microbes- In 1872, Koch became district medical officer for a rural area in berlin. He started to experiment with microbes in a small lab. He had built for himself in surgery.

• Discovery of Baciilus anthracis- The discovery that bacteria can act as specific agents of diseases in animals was given by Robert Koch, who first of all isolated Bacillus anthracis, the cause of anthrax which is devastating disease of cattle. In 1870, Robert Koch saw a large bacterium in the blood of anthrax victims. He reasoned that it might be agent of disease, but he knew that he would have difficulty in getting such a proposal accepted. He had no laboratory and his experiments were conducted in his home, using very primitive and improvised equipments and developing basic microbiological techniques. He painstaking teased out the anthrax bacterium and purified it. He then inoculated the purified bacteria into healthy animals and produced the classical clinical disease. When he examined the blood of inoculated animals, he was able to re-isolate the same bacterium. He repeated the isolation, infection and disease cycle until he was certain that he had found the agent of anthrax. Because it was such an important commercial disease because his technique could be easily duplicated others quickly verified his findings and Koch became famous.

• Discovery of new microbiological technique- He soon had his own institute and other discoveries followed. Koch attracted other bright scientists and together they developed the basic techniques of microbiology lab we still use today. These include:

- Sterile culture techniques.
- Pure culture techniques.
- Use of Petri plates, inoculation needles and solid medium
- Use of agar and gelatin to produce a solid surface.

• Use of cover slips- He also used cover slips for maintaining permanent records.

• Use of Gelatin- In 1881, Koch struggled with the disadvantage of using liquid media for certain experiments. He looked out for other alternatives including slices of potatoes as a solid culture medium. Potato slices could not be used for his animal pathogens, since these organisms did not grow on this substrate. He therefore employed gelatin s a solidifying agent and as a result was able to obtain individual colonies well separated from each other on the surface of gelatin medium.

Gelatin used by Koch to prepare solid media was not an ideal solidifying agent because of two important reasons:

- Since gelatin is a protein, many bacteria capable of producing proteolytic exoenzyme gelatinase that hydrolyses the proteins to amino acids digest it.

- It has a very low melting point i.e. it melts when temperature rises above 25°C.

Later Fannie Angelina Hesse first proposed the use of agar in culture media. She explained that Agar agar, a complex polysaccharide extracted from sea weed can be used as a solidifying agent because of following reasons:

- Non toxic to microbes
- Melts at 95 C but solidifies at about 45°C ( a temp. at which most bacteria can survive)
- Non-toxic to other forms of life.
- Stable to sterilization temperature.
- Physiologically inert as very few bacteria have the enzymes for digesting it.

• While Koch’s plating procedures provided advantages for the study of microorganisms, there was still problem of a suitable culture vessel. In 1887, Richard Petri solved this problem by what was known as Petri plates, a culture dish that is extensively used today.

Thus, contribution of Robert Koch, Fannie Hesse and Richard Petri made possible the isolation of pure culture of microorganisms and directly stimulated progress in all areas of microbiology.

• He systematically investigated the efficiency of chemical disinfectants demonstrating that carbolic acid used by Lister was merely bacteriostatic and bactericidal.

• He first recognized that disinfection depended on chemical concentration and contact time. He dried anthrax spores on silk threads, exposed them to disinfectants, washed them with sterile distilled water and cultured them to evaluate the range of chemicals.

• In 1882, he discovered Mycobacterium tuberculosis from tissues of a workman, stained it with methylene blue and observed blue colored rods.

• He also discovered and isolated the Vibrio cholerae, a causative agent of cholera and the importance of water filtration in the control of cholera.

• He proposed the concept of disease “Carriers.”

Koch was awarded Noble Prize in 1905 for his work. He will be remembered for both his discovery of important disease causing microorganisms and his fundamental contribution to Bacterial Techniques.

His vital contribution to microbiological methodology also makes him the “Founder of the field bacteriology.”







IMMUNIZATION ERA



5. Edward Jenner [1749-1823]

An English physician born in 1749 at Berkley (England) and died in 1823. He was a country doctor who had studied nature and his natural surroundings since childhood.

His notable contributions to microbiology are:

• Vaccine for smallpox- His great gift to world was his vaccine for smallpox. This disease was a horror as it killed in one in three of those who caught it and badly disfigured those who were lucky enough to survive catching it. Rural old wives that milkmaids only got a weak version of smallpox – non-life threatening smallpox but did not get smallpox itself had always fascinated him. A milkmaid who got cowpox got blisters on her hands and Jenner concluded that it must be pus in blisters that somehow protected milkmaids. To confirm his conclusion Jenner experimented on James Phipps (11 year old boy) where he injected the boy subsequently with tiny doses of pus and after that with smallpox. Amazingly the boy did not die, not even disfigured, just became ill for few days and recovered soon without any side effects. So successful was Jenner’s discovery , that in 1840 the government of the day banned any other treatment for smallpox than Jenner’s one.

• Vaccination– Jenner in 1798, published his results of 23 successful vaccinations. Eventually the process was known as vaccination based on latin word ‘vacca’ meaning cow.






6. Lord Joseph Lister [1827-1912]

Lord Joseph Lister was born in 1827 and died in 1912. He was a famous English surgeon. He is known for his notable contribution to antiseptic environment, for the precaution and cure of wound infections. He did not discover a new drug but he did make the link between lack of cleanliness in hospitals and deaths after operation.

His notable contributions to microbiology are:

• Wound infection by micro organisms- Lister impressed with Pasteur’s studies on the involvement of microorganisms in fermentation, concluded that wound infections too were due to microorganisms. Lister decided that wound itself had to be thoroughly cleaned. He then covered the wound with piece of lint covered in carbolic acid. He used this treatment on patients who had a compound fracture. It was the reason that the broken bone had penetrated the skin thus leaving wound that was open to germs. Death was so common by gangrene after such accidents. Lister covered the wound made with lint soaked in carbolic acid. His success rate for survival was very high.

• Development of antiseptic surgery- In 1867, he developed a system of antiseptic surgery designed to prevent micro organisms from entering wounds by application of phenol on surgical dressings and at times it was sprayed over surgical area.

• Antiseptic treatment- He also devised a method to destroy the micro organisms in the operation theatres by spraying fine mist of carbolic acid into air, thus producing antiseptic environment.

• Introduction of aseptic techniques- He also heated or sterilized the instruments to be used during surgery. Thus, he was fist to introduced aseptic technique for the control of microorganisms by the use of physical and chemical agents, which are still in use today.

Because of notable contributions Joseph Lister is known as Father of Antiseptic Surgery.




7. Elie metchnikoff [1845-1916]

One of the Pasteur’s associates Elie metchnikoff was a native of Ukraine. He was a Russian embryologist and immunologist; born in Kharkov in 1845, died in Paris in 1916. he studied natural sciences at university of Kharkov, in Germany and became professor of zoology in Odessa in 1867.

His notable contributions to microbiology are:

• Phagocytosis- Credit for coining the term Phagocytosis goes to him which literally mean phagocytose (eating of cell). In 1884, he published the account of phagocytosis and formulated the basic theory on which the science of immunology is founded i.e. body is protected from infection by leucocytes that engulf bacteria & other invading microbes.

While studying starfish larvae, he observed that certain cells engulfed splinters that he had introduced into larvae. These are called phagocytes.

• He formulated the theory that the phagocytes were body’s first and most important line of defense against infection.

• He became administrator at Pasteur institute in 1888 and eventually director.

For his discovery He alongwith Paul Ehrlich received Noble Prize in 1908.





ERA OF CHEMOTHERAPY-


Chemotherapy- can be defined as the use of chemicals that selectively inhibit or kill the pathogen without causing any damage to victim.
Two scientists Paul Ehrlich and Sakaherohatta (Japanese) discovered a drug Salvarsan which is an arsenobenzol compound in 1910 for treatment of disease of syphilis caused by Treponema pallidum.

Paul Ehrlich was responsible for lading an important foundation of era of chemotherapy. It was followed by Gerhard Domagk of Germany who, in 1935, reported Prontosil, a red dye used for staining leather, was active against pathogenic Streptococci and Staphylococci in mice. Although it had no effect against same infectious agent in test tube.

Two French scientist Jacques and Trefonal in same year showed that prontosil is broken down within body of mice to sulphanilamide ( i.e. sulpha drug) which was true active factor and Domagk was awarded Noble Prize in 1939 for the discovery of first sulpha drug.


8. Sir Alexander Fleming

Credit for the discovery of first wonder drug penicillin goes to Scottish physician and bacteriologist Sir Alexander Fleming in 1929 from mold Penicilliun notatum. He was born in year 1881 that was physician by training but spent much of his time on studying bacteria. He died in 1955.

• Discovery of penicillin- is fascinating accident. FLEMING was actually interested in searching something that would kill pathogen ever since working on wound infection during world war I (1914- 1918). One day in September in year 1928 upon return from a week vacation he observed that a plate of Staphylococcus aureus ha d contaminated with a green mold Penicillium notatum. It was forming a clear zone which has accidentally fallen on the plate and observed the plates, he noticed that colonies of P. notatum evidently being destroyed by bacteria.

Rather than discarding these contaminated plates he speculated that mold was producing a diffusible substance that inhibited growth of bacterium and Fleming became interested in subculturing for further studies and he extracted a compound from fungus which he named penicillin after the name of mold P. notatum and in year 1929 he published his findings in paper ‘Penicillin and its effects on gram positive bacteria’ Fleming’s work remain unnoticed until 1940 when Florey and Chain in 1941 at oxford university develop methods for industrial production of penicillin in England. When penicillin was finally produced in major quantity in 1941 its power and availability launched the antibiotic era, a major revolution in public health and medicine.

Because of the discovery and commercial production of penicillin all three Fleming, Florey and Chain shared Noble Prize in 1945.

P. notatum has been replaced by P. chrysogenum for the commercial production of penicillin and the latest strain yields 85000units/ ml of medium.

• Discovery of lysozyme- In 1920, Fleming searched an effective antiseptic. He discovered an enzyme called lysozyme in many body fluids such as tears. It had a natural antibacterial effect but not against strongest infectious agents.





ERA OF MOLECULAR BIOLOGY-


9. Joshua lederberg

Microbiology in 20 th century got a new era of molecular biology. With the recognition of unity of biochemical life processes in micro organisms and higher forms of life including human beings the use of micro organisms as a tool to explore fundamental life processes became attractive.

During 1940s a closer relationship was established between microbiologists, physicists biochemists and biologists resulting in creation of a new discipline which is now called molecular biology. Joshua Lederberg is among such a few renowned scientists who did great discoveries during the sense era and same field i.e. molecular biology. Joshua Lederberg is an American Genetists and Microbiologists who received the noble prize in 1958 for his work in bacteria. He was born in Montclair, near New York on 23 may, 1925. He was brought up in Washington. He served as a professor of genetics at the university of Washington then at Stanford school of medicine.

He has been actively involved in Artificial Intelligence Research and NASA experimental programs seeking life on mars.

His notable contributions to microbiology are:

• Conjugation- In 1946, Joshua Lederberg and Edward Tatum proposed conjugation in bacteria. The proof is based on generation of daughter cells able to grow in media that cannot support growth of either of parental cells. Their experiments showed that this type of gene exchange requires direct contact between bacteria. At the time lederberg began studying with tatum scientists believed that bacteria reproduced asexually but from the work of beadle and tatum lederberg knew that fungi reproduced sexually and he suspected that bacteria did as wellederberg

• Introduction of term plasmid- Joshual in 1952 used the term plasmid to describe extra chromosomal genetic material that replicate autonomously.

• Transduction- along with Norton zinder, lederberg discovered that genetic information could be transferred between bacteria by bacteriophage known as transduction. They gave a report on transduction in which the transfer of genetic material takes place by viruses. They showed that a phage salmonella typhimurium can carry DNA from one bacterium to another.

• Replica plating- along with his wife esther, lederberg discovered or developed a unique method of studying bacterial mutants now known as replica plating. With this technique it is possible to detect and isolate rare mutants with difeering nutritional requirements. Lederberg with this technique showed that mutations in bacteria occur randomly and spontaneously.

• One gene one enzyme- Joshua Lederberg, Beadle and Tatum started the relationships between genes and enzymes in 1941 using mutants of the bread mold fungus Neurospora crassa and gave the concept of one gene one enzyme hypothesis.

Also Lederberg, Beadle and Tatum were awarded Noble Prize in 1958 for the discovery of one gene one enzyme hypothesis.






10. Winogradsky and Beijerinck

The establishment of cardinal roles that microbes play in the biologically important cycles of matter on earth – the cycles of carbon, nitrogen and sulphur was largely the work of Winogradsky and Beijerinck.

His notable contributions to microbiology are:

• Importance of soil bacteria- The history of soil microbiology was opened in late 1800 by Winogradsky. He showed the importance of bacteria present in soil taking nitrogen from atmosphere, combating it with other elements, and thus making it available as plant food and hence animal food.

• Discovery of Azotobacter- in 1901, William Beijerinck found free living nitrogen fixing bacteria Azotobacter and described its usefulness in promoting soil fertility.

• Role of microbes- In cycles of Carbon, Nitrogen and Sulphur was observed by Winogradsky and Beijerinck and they discovered that many groups of microbes are specialized for carrying chemical transformations in soil that can not be formed by plants and animals.

• Microbial physiological specialization- Winogradsky discovered chemoautotrophic bacteria. These can grow in completely inorganic environments, obtaining energy necessary for their growth by the oxidation of reduced inorganic compounds and use carbon dioxide as the source of their cellular carbon. He also found several physiologically distinct groups among autotrophic bacteria i.e. sulphur bacteria, nitrifying bacteria.

• Atmospheric nitrogen fixation- Winogradsky and Beijerinck both contributed to the discovery that microbes play an important role in fixation of atmospheric nitrogen. They showed that certain bacteria, symbiotic or free living can use gaseous nitrogen for the synthesis of their cell constituents. These microbes help to maintain the supply of combined nitrogen, upto which all other forms of life are dependent.

• Enrichment culture- Both these developed a new and profoundly important technique enrichment culture for the isolation and supply of various physiological types of microbes that exist in nature.

Because of his notable contributions, Beijerinck is called as the Father of Virology.