(I A.)Pre golden era: History of Microbiology, Abiogenesis vs Biogenesis, Discovery of Microorganisms

(Unit I )Pre golden era:

History of Microbiology, Abiogenesis vs Biogenesis, Discovery of Microorganisms

The science of microbiology which come into existence with the discovery of the microscope may be said to had three period of development:

1.The  pre 1865 period, the ‘Pre Golden Era’, which experienced a slow accumulation of some facts about bacteria and other microbes  and a great deal of more or less correct speculation about them.

2. The period between 1865 and 1882 , the ‘Golden Era’, when the foundation of new science were securely laid especially through the pioneer work of the French scientist Louis Pasteur, the German physican Robert Koch and English Surgeon Joseph Lister and,

3.The post 1882 period, the ‘Post Golden Era’, extending to the present day, which experience rapid development of microbial information and a truly revolutionary application of this knowledge to human affairs.

 

History of Microbiology:

The term microbiology was given by French chemist Louis Pasteur (1822-95).

Microbiology is said to have its roots in the great expansion and development of the biological sciences that took place after 1850.

The term microbe was first used by Sedillot (1878).

Microbiology is the study of living organisms of microscopic size. OR

Microbiology is the study of organisms, called microorganisms that are too small to be perceived clearly by the unaided human eye.

If an object has a diameter of less than 0.1mm, the eye cannot perceive it at all, and very little detail can be perceived in an object with a diameter of 1mm.

Roughly speaking , therefore organism with a diameter of 1mm or less are microorganisms and fall into the broad domain of microbiology.

Microorganism have a wide taxonomic distribution they include some protozoa, many algae and fungi, bacteria and viruses.

The existence of this microbial world was unknown until the invention of microscopes.

Microscope ,optical instruments that serve to magnify objects so small that they cannot be clearly seen by the unaided human eye.

Microscopes, invented at the beginning of the seventeenth  century, opened the biological realm of the very small to systematic scientific exploration.

Eary microscope were of two kind.

The first were simple microscope  with a single lens.

The Second were compound microscopes with double lens system consist of an ocular and objective with greater magnification power.

However , nearly all the great original microscopic discoveries were made with simple microscopes.

Discovery of Microorganisms:

The discovery in microbiology got late start as compared to other science.

It started in mid 1600 because the powerful light microscopes were not available.

As the microorganism were the main important things in microbiology, their observation was necessary.

This was made possible by two scientists who developed the light microscope, Robert Hook and Antony van Leeuwenhoek.

Robert Hooke(1635-1703):

Robert Hooke made and used a compound microscope in 1660s and observed various materials.

With his microscope, he examined various materials and he presented his observations at the meeting of Royal Society of London.

And because of their response and encouragement, he published his observations in book called ‘Micrographia’.

This book contains detailed drawings of insects, insect larva, seeds eggs, feathers, hairs, rocks and cork.

In addition to this, Hooke described the microscopic forms of fungi commonly called as the molds.

 He also observed the spores of mushrooms. Although Hooks’s higest magnification were possibly encourage to observe bacteria but he made no observations of them.

Antony van Leeuwenhoek:

The discovery of  microbial world was a Dutch merchant Antony van Leeuwenhoek.

He was the first to observed the exciting and mysterious world of microorganism (1676 in Holland).

Antony van Leeuwenhoek was not a trained scientist but was self educated and familiar with glass blowing and fine metal work.

His microscope consisted of lenses, which provide greater magnification or resolving power, sufficient to visualize bacteria, protozoa and numerous other microorganisms.

The original object appeared 50-300 times greater with the use of microscope.

With such lenses Antony van Leeuwenhoek examined great variety of objects such as saliva, pepper infusions, cork, the leaves of plant, circulating blood in the capillary vessels in the tail of salamander, seminal fluid, urine, cow dung, scraping from his own teeth, and so on.

He sent his observations to Royal society of London.

After that he was called on by society and in 1680 elected him as a fellow.

For almost 50years, until his death in 1723, Antony van Leeuwenhoek transmitted his discoveries to the Royal socity of London in the form of a ling series of letter written in Dutch.

Most of these letters were translated in English.

O)ne of his microscopic consisted of two metal plates between which lens was placed.

The specimen was placed on the point of a blunt pin attached to a back plate.

For changing the position of specimen it was supported by two screws.

The construction was too simple but still he could observe variety of microbes and he constructed hundreds of such instruments, a few of which survi8ve today.

Antony van Leeuwenhoek’s place in scientific history was not only because of his skill as microscope maker but also his skill of microscopic observations.

His observations were descriptions of protozoa, algae, yeast and the various shapes of bacteria.

He made  observations of  microscopic structures of seeds and embryos of plants and on small invertebrate animals.

He discovered the existence of spermatozoa and red blood cells and was thus called the founder of animal histology.

He also discovered the capillary circulation of blood.

Robert Hooke with his microscope could not made very fine observations reported by Antony van Leeuwenhoek ,Thus Antony van Leeuwenhoek is considered as the ‘father of microbiology’.

After the death of Antony van Leeuwenhoek the study of microbiology was neglected for some time.

This was because of the difficulty in constructing  better microscopes and many  scientists considered microbes as nothing.

They were the believers of spontaneous generation theory.

Abiogenesis vs Biogenesis

After Antony van Leeuwenhoek’s discovery of microbial world scientists began to search for their origin.

Some believed that animalcules(organisms) were formed spontaneously from  the nonliving materials where as others formed from the seeds or germs of these animalcules, which were always present in air.

The theory of spontaneous generations was stated by Aristotle in 346 BC.

The theory of spontaneous generation or abiogenesis stated that living things  are spontaneously formed (originated) from the nonliving materials.

At that time the theory was was accepted without any questions because of the lack of knowledge about the microbes.

The example which put forward to support the theory of abiogenesis were ;snakes and frogs and related forms of life spontaneously develop from the mud of riverbanks and maggots and flies originated from  decaying food.

 One of the strong opponents to this theory was Francisco Redi, who refuse this theory and designed experiment to  disprove abiogenesis.

 

Francisco Redi and the Fly Experiments:

One of the first to refuse the theory of spontaneous generation was an Italian naturalist and physician Francisco redi .

Around 1665 he showed that maggots did not originaterd from decaying meat.

Redi put meat in three separates jars, one of which closed with a paper cover, another was open and the third was covered with wire gauze.

Naturally , the meat decayed and flies attracted towards it.

From this experiment Redi made following observations.

1)The paper covered jar showed no evidence of any maggots as there was no way to enter flies in the jar.

2) In the second jar which was open , flies and maggots and newly emerging  adult flies appeared.

3) Although no maggots and flies appeared on the meat in  jar covered with wire gauze, the smell of meat attracted the flies , but because of  wire gauze , they unable to enter in the jar .

And thus flies gathered on gauze and laid their eggs on the gauze.

After some time adults larvae (maggots) , come out of these eggs.

Hence no appearance of maggots and flies  in meat.

Thus he showed that maggots that appeared in decaying meat are the level  stages  of flies  and will never appear in meat if meat is protected by placing it in jar closed with wire gauze or paper.

By such experiment Redi destroyed the myth that maggots develops spontaneously from meat.

Louis Paster and Goose/Swan/S-necked flask:

Pasteur first demonstrated that air does contain microscopic  ‘organized bodies’.

Pasteur also designed experiments to disprove the theory of spontaneous generation.

He passed the air through a tube with a plug of cotton as filter.

Then the piece of cotton was dissolved in an alcohol ether mixture, and the sediments was examined under microscope.

Pasteur found small round oval bodies.

A small portion of this sediment was then added to sterile nutrient medium.

Soon the growth was observed.

In this way Pasteur come to know the source of microbes i.e. air.

To disprove the theory of spontaneous generation Pasteur designed and used Swan necked flask.

Nutrient liquid medium were placed in the  flasks and both the liquid media and flasks was sterilized by boiling.

Here no  plug were used to prevent the passage of microorganisms into flask.

The air was allowed to pass through the S-shaped tube, no growth occurred, because of the neck in the U-shaped tube.

However, if the top of the flask was broken off or if the flask were tilted so that  the sterile nutrient medium ran into the exposed part of the neck, where the dust particles were present in the liquid media.

This experiment showed that microbes did not originated  spontaneously  from the liquid media (non living matter), but they are present in air attached to the dust particles.

 

John Tyndall:

The final results of disproving spontaneous generation theory or abiogenesis were given by John Tyndall in 1877.

During his work on scattering of light by atmospheric dust, he observed that a beam of light passing through the air was visible because of the suspended dust particles scatter the light.

This phenomenon of scattering of light was termed as Tyndall’s effect.

 Tyndall was aware of Pasture’s finding of presence of microorganisms on dust particles.

Thus to prove the presence of microorganism on dust particles and to disprove the theory of spontaneous generation, Tyndall devised a system.

He built a wooden chamber , with a glass window on two opposite sides.

The inside surface of these box was coated with glycerol to trap the dust particles.

This chamber was fitted with  glycerol to trap the dust particles.

This chamber was fitted with boiled broth medium.

The air was allowed to pass through the tube at top, which had vertical bends.

A beam of light was allowed to pass through side e\windows to  visualize or see the dust particles, if present.

Tyndall observed no growth in the tubes with media, since the dust particles in air were settle in bent tubes.

Thus he concluded that the growth appeared in media, only when the particles in air enter in it.

But the exposure of media to air which is free of dust particles does not lead to growth of microbes in media.

In this way he proved that the microorganisms were present on dust particles and they did not originated from organic matter.

This was the final experiment to disprove the theory of spontaneous generation or abiogenesis.

After long studies on bacteria and their heat resistance, Tyndall concluded that certain bacteria existed in two forms; thermolabile and thermostable.

Thermolabile form was killed by a few minutes exposure to boiling temperature i.e. heat sensitive.

The thermostable form was resistant  to boiling for several hours.

These heat resist bacterial structures are now called as spores.

Spores were independently found and named in 1877 by the German bacteriologists Ferdinand Cohn.

While attempting to  repeat the studies on dust containing environments, Tyndall used hay in medium.

But the experiments were failed and the growth appeared in boiled hay broth medium.

This was because hay was containing too many spores producing bacteria, which were resistant to boiling.

Thus in an attempt to kill spores producing bavteria, Tyndall developed a sterilization procedure which latter become known tyndallization.

Thus the two forms thermostable and thermolabile are spores and vegetative cells respectively.

In case of spore producing bacteria i.e. heat resistant bacteria, when the temperature increased ,the bacteria forms a spore in the cell and after that the vegetative cell lysis occurs and the spores come oput, which survives.

Thus spores resist high temperature .

And whenever the temperature comes down to normal, spores germinates to form vegetative cell.

The vegetative cells are sensitive to high temperature and are easily killed.

This is the principle of Tyndallization process.

Tyndallization involved the boiling of nutrient media for three successive days and its incubation at room temperature in between heating.

The vegetative forms or growing bacteria are easily killed by boiling  but spores are not.

During incubation period the heat resistant spores germinate tpo form vegetative cell, which are then killed by agin boiling.

In this way during Tyndallization process, the spores are allowed to germinate and killed.

Thus this process is very useful to kill spores or spore forming bacteria, which are not normally killed by simple heating treatment, because of their heat resistance.

Refernce: 1.Microbiology by S.J.Sathe.page no 5-6.

                       2. General microbiology by Stanier 1-7.

                          3. Microbiology, by Prescott