BIOREADERS: Bacteria 🦠

BACTERIA

From previous studies we found that bacteria is a prokaryotic organism i.e., they lack nuclear envelope. Nucleus is formed first time in these organisms. The bacteria generally terms to Eubacteria.

Many experiments had done to find the first occurred organism on the earth. Through evidences and experiments bacteria are found to be the first formed organism on the earth. ANTONIE VAN LEEUWENHOEK was the scientist who first found the live protozoa and bacteria through microscope and named them as “animal cules”. Before that let us know about how the primitive organism is formed and how were they identified.

Scientist’s theories and experiments on how primitive organism is formed:

Abiogenesis:

Many scientists gave theories and conducted experiments on how the primitive organisms are formed. Few scientists thought that they were generated spontaneously. Francesco Redi was the first scientist to conduct experiments on spontaneous generation. In 1668 Francesco Redi, an Italian Physician, performed an experiment on maggots whether they were evolved from the decaying food or not. For this he had taken meat in few jars which half of them are fully covered other half of them are kept opened. He observed that maggots developed only from the meat in a jar which is kept opened. Later in 1767, Lazzaro Spallanzani, an Italian priest and biologist conducted experiments on spontaneous generation of microorganisms. For this he had taken four jars in which broth or infusions are poured.

1. Flask 1: Left open. The broth turned cloudy after few minutes found that presence of microorganisms.

2. Flask 2: Sealed. The broth turned cloudy after few minutes found that presence of microorganisms.

3. Flask 3: heated broth with opened mouth. The broth turned cloudy after few minutes found that presence of microorganisms.

Flask 4: Heated broth with sealed mouth. No appearance of broth turned cloudy and found that absence of microorganisms. At this time oxygen was discovered as a breathing gas which allows microbes to grow. They found that oxygen is excluded out and it was the reason that microbes didn’t allowed to grow on the broth.

From this experiment he said that the microorganisms are airborne. But he was failed in explaining spontaneous generation of microbes but found that the microorganisms can be killed by heating.

Louis Pasteur, a French organic chemist in 18^th showed that growth did not occur in broth or infusions which had been heated but exposed to air provided the incoming air was treated to remove the microorganisms. He demonstrated that air contains microscopically observable organized structures. He exhaled a large quantity of air through a tube that contained a plug of gun cotton to serve as a filter. The gun cotton was then removed and dissolved in a mixture of alcohol-ether and the sediment was examined microscopically. He found that this sediment contained not only organic matter but also a large number of small round structures which are identical to microorganisms. From this experiment he found that the microbes are already present in the air and are reason for the spoilage of infusions. Louis also conducted another experiment called swam neck experiment.

To prove that infusions which are once heated can be kept sterile, if kept from air

containing micro organisms, he sterilized infusions in flask with open S-shaped

tubes. These flasks containing sterile infusions had free access to air but the air

had to pass through the S-shaped tube. The result was that the dust particles and microorganisms in the air settled at the bend and did not reach the infusion, thus keeping the infusion sterile. Growth was however possible if the infusions were tipped into the S-shaped tube and allowed to run back. However from his experiments he had found that microorganisms are not spontaneously generated but they come from life. This theory is also known as theory of biogenesis.

With Louis Pasteur statements John Tyndall, an English Physicist also supported that the sterile infusions placed in a dust free chamber could remain sterile indefinitely even if kept exposed to air. While Tyndall, during his experiments he found that a different type of infusions takes different lengths of heating. For example, vegetable infusions can be sterilized for 5 minutes in boiling brine, while hay infusions were failed to sterilize. From this experiment he concluded that some microorganisms exist in two forms – one is heat labile and other is heat resistant form. Former is vegetative and latter is endospore and the spoilage is due to development of endospore into vegetative form after cooling. Through this process of intermittent heating and cooling to preserve food materials is known to be as “Tyndallization”. During this process neither growth nor spoilage occurred.

Finally, these scientists were stated that microorganisms generated from existing life but not from non-life and it is called as BIOGENESIS.

Aristotle, Thales, Plato and Von Helmont also stated that life originated from non living matter, decaying organic matter, etc. They supported the idea of Abiogenesis.

“Theory of special creation” states that species on the earth were created by a divine power

Theory of origin of life or theory of Coacervative: (Biogenesis)

Theory of origin of life or Coacervate theory proposed by A.I. Oparin and supported by J.B.S. Haldane. They stated the organisms are evolved over billions of years ago by natural calamities like volcanic eruption, U.V radiation, lightning etc.

Chemical evolution to Biological evolution:

In chemical evolution primitive atmosphere was formed. Then simple organic molecules and later complex organisms were formed. Over 4 to 3.5 Eons ago the earth’s temperature was about 4000˚C to 6000˚C which was gradually cooled down over millions of years. During this process primitive atmosphere known as reducing atmosphere is formed by the light elements such as helium, carbon, hydrogen, nitrogen etc. this was hot with abundant hydrogen and without oxygen. The molecules formed by the elements or atoms such as ammonia, methane etc., mineral rocks, were washed down to the oceans, rivers etc. along with the rain water leading to the accumulation of minerals in the sea water. These combine with the hydrocarbons condensed by the highly reactive radicals (CH₂^-, CH^-) to form simple organic molecules like sugars, amino acids, fatty acids, purines, pyrimidines which later formed nucleosides and nucleotides. This is considered as hot dilute soup or prebiotic soup by J.B.S. Haldane. In this prebiotic soup simple organic molecules are formed into complex polymers like polysaccharides, proteins, fats and nucleic acids. Nucleic acids and proteins combined to form nucleoprotein. This is done under oxygenless atmosphere through the action of sunlight.

From this complex organic molecules bubble like droplets were formed due to intermolecular forces called Coacervates. These droplets grow by fusion with other droplets and reproduce through fission into daughter droplets. Gradually they attain features like lipid membranes, enzymes which enhance the fast multiplication of molecules, fast rate of metabolic activities by the free genes.

Firstly chemoautotrophic, anaerobic heterotrophs were evolved under harsh conditions (at high temperatures) by gaining energy by the fermentation of some organic molecules. Example: Iron and Sulphur bacteria. These take-in carbondiaxide and convert into chemical energy to make carbohydrates and sugars. Some other bacteria called purple and green sulphur bacteria synthesized bacterial chlorophylls from magnesium prophyrins which can trap solar energy and fix carbondiaxide. These were the anoxygenic photosynthetic chemoautotrophs. Later the bacterial chlorophyll evolved into the true chlorophyll as in cyanobacteria and plants. As a result, oxygenic photoautotrophs were evolved. Example: Blue green algae. By this process reducing atmosphere is gradually changed into oxidizing atmosphere i.e., oxygen is started producing. Gradually these lead to generation of anaerobes with aerobic mode of respiration.

Life from chemical to biological

A.I.Oparin J.B.S.Haldane

Urey-Miller Experiment:

The chemical evolution was experimentally proven by two scientists. They were Stanley Miller and Harold Urey. The experiment was called as Urey-Miller experiment.

They intend to prove that organic elements were evolved from the inorganic elements by providing primordial atmospheric conditions. The water glass which is kept to heat represents primordial reducing atmosphere. It is cooled down gradually form vapors. Ammonia, methane, hydrogen gases were formed in the moist environment in which the glass is arranged with two electrodes (assumption of lightning). Due to lightning effect organic compounds were started to generate after few days. Later they noticed simple amino acids such as glycine, alanine, aspartic acid, glutamic acid and other organic compounds such as urea, lactic acid, glycolic acid, succinic acid and propionic acid were formed in it. From this they were concluded that the organic compounds were formed from the inorganic substances.