History of Microbiology; Theory of Spontaneous Generation Vs Biogenesis- Dr C R Meera

 

Microorganisms are closely related to our day today life. Many of the microorganisms are beneficial to mankind whereas others are detrimental. Beneficial effects of microbes are numerous. Microbes are involved in fermentation of idli batter, making of curd, bread, yogurt, cheese, wine and such so many food products. They are also involved in the production of many antibiotics, antiviral agents (interferons) etc. Microbes are the primary decomposers on earth playing a major role in the biogeocycling of organic compounds. At the same time harmful microbes cause many diseases, spoilage food and deterioration of materials like iron pipes, wood pilings etc.      

In Greek “Mikros” means “too small to be seen with the naked eyes”, “bio” means “life” and “ology” means “study of”. Microbiology is the study of living organisms that cannot be seen with our naked eyes or it is the study of “microorganisms”. Microorganisms include bacteria, protozoans, algae, parasites, fungi (Yeasts and, molds) and viruses.

Study of different groups of microorganisms are named as follows:

1. Bacteria                                               - Bacteriology

2. Protozoans                                          - Protozoology

3. Algae                                                   - Phycology

4. Parasites                                              - Parasitology

5. Yeasts and Molds (Fungi)                  - Mycology

6. Viruses                                                - Virology

In ancient times, it was believed that diseases are punishment for an individual's crime, or they are due to evil spirit or poisonous vapours from rotting organic matter. Existence of microorganisms was not known at that time.  First proponents of the idea that invisible organisms caused diseases, were Lucretius (B.C.) and Girolamo Fracastoro (1546).

Earliest microscopic observations were made by Francesco Stelluti and Robert Hooke. Francesco Stelluti, an Italian naturalist made first microscopic observations on bees and weevils, by using the microscope probably supplied by Galileo. Later microscopic observations and studies were done by Robert Hooke. Micrographia is a historically significant book by Robert Hooke about his observations through various lenses. It was the first book to illustrate insects, plants etc. as seen through microscopes. Published in January 1665, the first major publication of the Royal Society, London, it became the first scientific best-seller, inspiring a wide public interest in the new science of microscopy.

Theory of Spontaneous generation (Abiogenesis) Vs Theory of Biogenesis

Earlier in 17^th Century, it was believed that living creatures could arise from non-living matter. For instance, it was hypothesized that certain forms such as fleas could arise from inanimate matter such as dust, or maggots could arise from dead flesh or mud. Means, living things can originate from non- living things and this theory was called the “Theory of spontaneous generation” or “Theory of Abiogenesis”. This theory was put forward by the Greek Philosopher Anaximander.  Greek Philosopher Aristotle also supported the theory of spontaneous generation and concluded that even some invertebrates could arise from non-living matter by spontaneous generation.

The theory of spontaneous generation was first challenged by Italian physician Francesco  Redi. His experiments on decaying meat to disprove the theory of abiogenesis is known as Redi’s experiment. To test the hypothesis, Francesco Redi placed fresh meat in open containers [left]. As expected, the rotting meat attracted flies, and the meat was soon swarming with maggots (larvae of flies), which hatched into flies. Then he covered a jar with air tight material, so that flies could not get in [middle] and no maggots were produced from meat. To answer the objection that the air tight cover might have cut off fresh air necessary for spontaneous generation, Redi covered the third jar with porous gauze [right] instead of an air-tight cover. Flies were attracted to the smell of the rotting meat, clustered on the gauze, which was soon swarming with maggots, but the meat itself remained free of maggots. Thus he proved that flies are necessary to produce flies: they do not arise spontaneously from rotting meat. Life originate only from living forms and is known as the “Theory of Biogenesis”.

Antony van Leeuwenhoek, a Dutch businessman and scientist is known as the “Father of Microbiology”. He was a cloth merchant. While running his draper shop, Van Leeuwenhoek wanted to see the quality of the thread better, by using the magnifying lenses. He developed an interest in lens making and it became his hobby. Leeuwenhoek made over 500 magnifying lenses and at least 25 single-lens microscopes during his lifetime. He started to observe drops of liquid like blood or pond-water etc., solid samples like as plant material or animal muscles etc.

His microscopes were made of silver or copper frames, holding hand-made lenses. The single-lens microscopes of Van Leeuwenhoek were relatively small devices, the largest being about 5 cm long. They were used by placing the lens very close in front of the eye, while looking in the direction of the sun. The other side of the microscope had a pin, where the sample was attached in order to stay close to the lens. There were also three screws to move the pin and the sample. He had made around 500 lenses and 25 single lens microscopes in his life time. But throughout his life the aspects of microscope construction and making of lenses, he kept as a secret.

The first microorganisms he observed under microscope were protozoans. He was also the first to record microscopic observations of muscle fibers, bacteria, spermatozoa and blood flow in small blood vessels. Van Leeuwenhoek did not write books, but sent letters to the Royal Society in London. He had also made drawings of moving “animalcules”. The letters were published in the Royal Society's journal Philosophical Transactions of the Royal Society. His observations laid the foundations for the sciences of bacteriology and protozoology and paved way to the development of new branch of science, Microbiology.

Leeuwenhoek’s discovery of microbes renewed the controversy between theory of Abiogenesis and Biogenesis. In 1748, another scientist John Needham challenged Redi’s findings and supported spontaneous generation of microbes by showing that even after boiling mutton broth and pouring into sealed containers, showed the growth of microbes. In this experiment he placed the broth in a bottle, heated the bottle to kill anything inside and then sealed it. Days later, he reported the presence of life in the broth as indicated by the development of turbidity and said that life had been created from nonlife. Actually, he did not heat it long enough to kill all the living forms in it.

In 1776, Lazzaro Spallanzani, an Italian scientist, again challenged the theory of spontaneous generation. Lazzaro Spallanzani, reviewed both Redi's and Needham's data and experimental design and concluded that perhaps Needham's heating of the bottle did not kill all living forms present in the broth. He constructed his own experiment by placing broth in each of two separate bottles. He boiled the broth in both bottles, then sealed one bottle tightly and left the other open. Days later, the unsealed bottle was teeming with small living things and the sealed bottle showed no signs of life. This experiment certainly excluded spontaneous generation as a viable theory.

In 1861, Louis Pasteur, Famous French scientist rigorously disproved the theory of spontaneous generation through his “Swan Neck Experiment”.  He designed   S-curve necked flasks (Swan necked or Goose necked flask) that were oriented downwards, so gravity would prevent access by airborne foreign materials. He placed nutrient-enriched broth in one of the goose-necked bottles, boiled the broth inside and left for few days. No life was observed in the jar. He then broke off the top of the bottle, exposing it more directly to the air, and noted life-forms in the broth within days. He noted that as long as dust and other airborne particles were trapped in the S-shaped neck of the bottle, no growth was observed in the broth. He reasoned that the contamination came from life-forms in the air and that only caused growth in broth. Hence he concluded that life originate only from living forms. Pasteur is known as the “Father of Modern Microbiology” and has made a number of significant of contributions to the field of Microbiology.

Louis Pasteur

Pasteur's Swan neck experiment

The mid 1800s to the early 1900s saw the rise of first microbiologists and is called the “Golden age of Microbiology”. During the golden age, many pathogens were identified, vaccines were developed, methodologies were perfected and foundations were established that support today’s modern research. These experiments and developments in this field led to the development of Microbiology as a new branch of science.

 

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