Historical Development and Milestones of Microbiology

HISTORICAL DEVELOPMENT OF MICROBIOLOGY - MILESTONES

It is more or less a gospel truth that in science the ultimate credit, glory, and fame goes to the one who actually succeeds to convince the world, and not to the one who first had conceived the original concept and idea. Hence, in the development of microbiology the most popular and common names are invariably of those researchers/scientists who not only convinced the world in general, but also developed a tool or a specific technique or an idea (concept) which was virtually adopted or who expa-tiated their observations/findings rather vividly or astronomically that the science grew and prospered in particular.

Evidence from the literature reveals that Antony van Leeuwenhoek’s (1632-1723) lucid expla-nations with regard to the ubiquitous (i.e., found everywhere) nature of the microbes practically enabled Louis Pasteur (1822–1895) almost after two centuries to discover the involvement of these microorgan-isms in a variety of fermentation reaction procedures that eventually permitted Robert Koch (1843-1910), Theobald Smith, Pasteur and many others to establish and ascertain the intimate relationship of the various types of microbes with a wide range of dreadful human diseases. In fact, Robert Koch bagged the most prestigious Nobel prize in the year 1905 for his spectacular and wonderful discovery for the isolation and characterization of the bacteria that cause anthrax*** and tuberculosis.****

With the passage of time the ‘mankind’ has won several gruesome battles with dreadful micro-organisms quite successfully and have adequately mustered the knack not only to make them work in an useful and beneficial manner but also to control and prevent some of those that are rather dangerous and harmful in nature.

1. The Microscope

The evolution of microscope gathered momentum in the year 1674, when a Dutch cloth mer-chant Antony van Leeuwenhoek first of all had a glimpse at a drop of lake-water via a lens made of glass that he had ground himself. Through this simple device using a magnifying lens Leeuwenhoek first and foremost ever had an ‘amazing sight’ of the most fascinating world of the microbes.

BOD : Biological oxidation demand.

COD : Chemical oxidation demand.

Anthrax : Acute infectious disease caused by Bacillus anthracis, usually attacking cattle sheep, horses, and goats. Humans contract it from contact with animal hair, hides or waste.

Tuberculosis [TB]. An infectious disease caused by the tubercle bacillus, Mycobacterium tuberculosis, and characterized pathologically by inflammatory infiltrations, formation of tubercles, necrosis, abscesses, fibrosis, and calcification.

Later on, Leeuwenhoek critically and explicitly described the finer details of a plethora of micro-organisms viz., protozoa, algae, yeast, and bacteria to the august Royal Society of London (UK) in a series of letters. It is worthwhile to mention here that the entire description was so precise and accurate that as to date it is now quite possible to assign them into each particular genera without any additional description whatsoever.

The earlier observations of microorganisms were made duly by several researchers chronologi-cally as given below :

Roger Bacon (1220–1292) : first ever postulated that a disease is caused by invisible living creatures.

Girolamo Fracastoro (1483–1553) and Anton von Plenciz (1762) : these two reseachers also made similar observations, assertions, and suggestions but without any experimental concrete evidences/ proofs.

Athanasius Kircher (1601–1680) : made reference of these ‘worms’ that are practically invis-ible to the naked eyes and found in decaying meat, milk, bodies, and diarrheal secretions. Kircher was, in fact, the pioneer in pronouncing the cognizance and significance of bacteria and other microbes in disease(s).

Antony van Leeuwenhoek (1632–1723) : initiated the herculian task of ‘microscope making’ through his inherent hobby of ‘lens making’. During his lifespan stretching over to 89 years he meticu-lously designed more than 250 microscopes ; of which the most powerful one could magnify about 200-300 times only. However, these microscopes do not have any resemblance to the present day ‘com-pound light microscope’ that has the ability to even magnify from 1,000-3,000 times.

2. Spontaneous Generation Vs Biogenesis

The wonderful discovery of microbes both generated and spurred enough interest not only in the fundamental origin of ‘living things’ but also augmented argument and speculation alike.

Based upon the various experimental evidences the following observations were duly made by scientists as enumerated below :

John Needham (1713-1781) : Precisely in the year 1749, while experimenting with raw meat being exposed to hot ashes, he observed meticulously the appearance of organisms that were not present at the initial stages; and, therefore, inferred that the bacteria virtually originated from the raw meat itself.

Lazaro Spallanzani (1729-1799) : actually boiled ‘beef broth’ for a duration of 60 minutes, and subsequently sealed the flasks tightly. After usual incubation for a certain length of time, practi-cally no microbes appeared. However, Needham never got convinced with Spallanzani’s findings, and vehemently insisted that ‘air’ happened to be an essential component to the process of spontaneous generation of the microbes, and that it had been adequately excluded from the flasks by sealing them precisely by the later.

Franz Schulze (1815-1873) and Theodor Schwann (1810–1882) : these two scientists inde-pendently fully endorsed and justified the earlier findings of Spallanzani by allowing air to pass through strong acid solutions into the boiled infusions, and by passing air into the flasks via red-hot tubes respectively (Fig. 1.A). In neither instance did microorganisms appear.

Special Note : The stubbornly conservative advocates of the theory of ‘spontaneous generation’ were hardly convinced by the aforesaid experimental evidences.

H. Schroder and T. von Dusch (~ 1850) : carried out a more logical and convincing experimental design by passing air via cotton fibers so as to prevent the bacterial growth ; and thus, it ultimately initiated and gave rise to a basic technique of ‘plugging’ bacterial culture tubes with ‘cotton plugs’ (stoppers), which technique being used still as to date (Fig. : 1.B).

Felix Archimede Pouchet (1800–1872) : revived once again the concept and ideology of spon-taneous generation via a published comprehensive and extensive research article thereby proving its occurrence. Pasteur (1822–1895) carried out a number of experiments that virtually helped in conclud-ing the on-going argument once for all time. Pasteur designed a flask having a long and narrow gooseneck outlet (Fig. : 1.C). Thus, the nutrient broths were duly heated in the above specially–designed flask, whereby the air — untreated and unfiltered — may pass in or out but the germs settled in the ‘very gooseneck’ ; and, therefore, practically no microbes ultimately appeared in the nutrient broth (solution).

John Tyndall (1820-1893) : conducted finally various well planned experiments in a specifi-cally designed box (Fig. : 1.D) to establish and prove the fact that ‘dust’ actually contained and carried the ‘microbes’ (i.e., germs). He subsequently demonstrated beyond any reasonable doubt that in a particular situation whereby absolutely no dust was present, the sterile nutrient broth could remain free of any sort of microbial growth for an indefinite length of time.

3. Fermentation

France having the strategical geographical location developed the commercial manufacture of a large variety of wines and beer as a principal industry. Pasteur played a critical and major role in the proper standardization of various processes and techniques intimately associated with the said two ‘alcoholic beverages’ in order to obtain a consistently good product. Pasteur used his God gifted won-derful skill and wisdom to explore and exploit the unique capabilities of microbes in the fermentation industry exclusively using fruits and grains resulting in alcohol-based table wines, dry-wines, cham-pagne, whiskies, etc. Pasteur meticulously isolated, typified, and characterized ‘certain microbes’ ex-clusively responsible for the ‘good batches’ predominantly in comparison to the ones found solely in the ‘poor products’.

In fact, the overall net outcome of such extensive as well as intensive investigations helped in a long way for the assured and successful production of consistently good and uniform ultimate product. Pasteur vehemently argued and suggested that the unwanted/undesirable types of microbes must be destroyed and removed by heating not enough to alter the original and authentic inherent flavour/aroma of the fruit juice, but just sufficient to cause and afford the legitimate destruction of a relatively very high percentage of the ‘bad microbial population’. This ‘destructive microbial phenomenon’ could be ac-complished successfully by holding the juices at a temperature of 145°F (≡ 62.8°C) for a duration of 30 minutes.

Pasteurization. Nowadays, the large-scale handling of such destructive microbial process may be achieved by ‘pasteurization’* in commercial fermentation industries using either ‘malt wort’ (having ~ 10% solids) or molasses (~ 10% solids) or even fruit-juices.

4. Germ Theory

A plethora of observant researchers had already conceptualized and opined rather vehemently the much applauded and widely accepted ‘germ theory’ of disease even before Pasteur established experimentally that microbes (or bacteria) happen to be the root cause of several human dreadful diseases. Later on various other scientists supported and proved the aforesaid ‘germ theory’ in one way or the other as stated under :

Girolamo Fracastro (1483–1553) : advocated that certain diseases might be caused by virtue of invisible organisms transmitted from one subject to another.

Plenciz (1762) : stated that the living microbes (or agents) are the ultimate cause of disease but at the same time aired his views that different germs were responsible for different ailments.

Oliver Wendell Holmes (1809–1894) : suggested that puerperal fever** was highly conta-gious in nature ; besides, it was perhaps caused by a germ carried eventually from one mother to another either by midwives or physicians.

Ignaz Philipp Semmelweis (1818–1865) : pioneered the usage of antiseptics specifically in the obstetrical practices.

Joseph Lister (1890) : made known in England the importance of antisepsis, which was subse-quently fully appreciated by the medical profession all and sundry.

Robert Koch (1843–1910) : discovered the typical bacilli having squarish ends in the blood sample of cattle that had died due to anthrax.*

Koch’s Modus Operandi — Koch adopted the following steps to isolate microbes causing anthrax :

(1) First of all these bacteria were duly grown in cultures in the laboratory.

(2) Bacteria examined microscopically so as to ascertain only one specific type was present.

(3) Injected bacteria into other animals to observe whether they got also infected, and subsequently developed clinical symptoms of anthrax.

(4) Isolated microbes from experimentally infected animals squarely matched with those ob-tained originally from sheep that died due to infection of anthrax.

Koch’s Postulates : The series of vital observations ultimately led to the establishment of Koch’s postulates, that essentially provided four vital guidelines to identify the particular causative agent for an infectious disease, namely :

(a) A particular microbe (organism) may invariably be found in association with a given disease.

(b) The organism may be isolated and cultivated in pure culture in the laboratory.

(c) The pure culture shall be able to cause the disease after being duly inoculated into a susceptible animal.

(d) It should be quite possible to recover conveniently the causative organism in its pure culture right from the infected experimental animal.

5. Classical Laboratory Methods and Pure Cultures

Microorganisms are abundantly found in nature in sufficiently large populations invariably com-prised of a plethora of different species. It is, however, pertinent to state here that to enable one to carry out an elaborated study with regard to the characteristic features of a specific species it is absolutely necessary to have it separated from all the other species.

Laboratory Methods: Well defined, articulated, and explicite laboratory methods have been adequately developed which enable it to isolate a host of microorganisms representing each species, besides to cultivate each of the species individually.

Pure Culture : Pure culture may be defined as — ‘the propogation of microorganisms or of living tissue cells in special media that are conducive to their growth’.

In other words it may also be explained as the growth of mass of cells belonging to the same species in a laboratory vessel (e.g., a test tube). It was indeed Joseph Lister, in 1878, who first and foremost could lay hand on pure cultures of bacteria by the aid of ‘serial dilution technique’ in liquid media.

Example : Lister diluted milk, comprising of a mixture of bacteria, with a specially designed syringe until a ‘single organism’ was strategically delivered into a container of sterile milk. The con-tainer on being subjected to incubation for a definite period gave rise to a bacteria of a single type, very much akin to the parent cell. Lister termed it as Bacterium lactis.

Colonies : Koch meticulously devised methods for the specific study of microorganism. He smeared bacteria on a sterile glass slide, followed by addition of certain specific dyes so as to observe the individual cells more vividly under a microscope. Koch carefully incorporated some specific solidifying agents, such as : gelatin, agar into the media in order to obtain characteristic isolated growths of organisms usually called as colonies. Importantly, each colony is essentially comprised of millions of individual bacterial cells packed tightly together.

Now, from these identified colonies one may transfer pure cultures to other sterile media. How-ever, the development of a liquefiable solid-culture medium proved to be of immense fundamental importance.

Example : Koch thoroughly examined material obtained from subjects suffering from pulmo-nary tuberculosis, and succeeded in the isolation of the tubercle bacillus Mycobacterium tuberculosis.

In conclusion, one may summarize the remarkable importance of ‘pure cultures’ toward the overwhelming development in the field of microbiology, because by the help of pure-culture techniques several intricate and complicated problems could be answered with reasonable clarification and complete satisfaction, namely :

·        Microorganisms causing a large number of infections,

·        Certain specific fermentative procedures,

·        Nitrogen-fixation in soil,

·        High-yielding alcohol producing strains from ‘malt wort’, and ‘molasses’,

·        Selected good cultures for making top-quality wines, and

·        Specific cultures for manufacturing dairy products viz., cheeses, yogurt.

Futuristic Goals

The futuristic goals of ‘pure cultures’ are exclusively based upon the following two cardinal aspects, namely :

(a) better understanding of the physiology of individual microorganisms present in the pure culture, and

(b) ecological relationships of the entire microbial populations in a given environment.

Thus, the following new horizons in the domain of microbiology may be explored with great zeal and gusto :

·        Advancements in marine microbiology,

·        Rumen microbiology,

·        Microbiology of the gastro-intestinal tract (GIT), and

·        Several other systems.

6. Immunity

Immunity refers to the state of being immune to or protected from a disease, especially an infectious disease. This state is invariably induced by having been exposed to the antigenic marker on an organism that invades the body or by having been immunized with a vaccine capable of stimulating production of specific antibodies.

Interestingly, Pasteur’s practical aspects and Koch’s theoretical aspects jointly established the fact that the attenuated microorganisms* retained their capacity and capability for stimulating the respective host to produce certain highly specific substances i.e., antibodies** which critically protect against subsequent exposure to the virulent organisms.***

Examples :

(a) Edward Jenner’s successful cowpox vaccine (in 1798) : Jenner’s epoch-making successful attempts in vaccinating (innoculating) patients with cowpox vaccine, that ultimately re-sulted in the development of resistance to the most dreadful smallpox infection.

(b) Pasteur’s successful rabies vaccine : Pasteur’s charismatic fame and reputation became well known throughout France when he successfully prepared rabies vaccine by innoculating a rabbit with the saliva from a rabid dog. The healthy rabbit contracted the rabies virus and died later on. The extract of dead rabbit’s brain and spinal cord were duly attenuated and injected into rabies patient who eventually survived later on. Thus, the vaccine for rabies or hydrophobia — a disease transmitted to humans through bites of dogs, cats, monkeys, and other animals.

7. Medical Microbiology

Interestingly, the ‘germ theory’ of disease was very much in existence for a long duration ; however, the direct implication and involvement of germs in causing disease was not well established, and hence recognized and widely accepted.

The magnificent and remarkable success of Louis Pasteur and Robert Koch not only earned them befitting honours and accolades from their beloved countrymen, but also rewarded them by bestowing their gratitude in establishing the famous and prestigious Pasteur Institute in Paris (1888), and Professor of Hygiene and Director of the Institute for Infective Diseases in the University of Berlin respectively.

At this point in time altogether newer microorganisms (bacteria) were being discovered with an ever-increasing speed and momentum, and their disease-producing capabilities were adequately estab-lished and proved by Koch’s four cardinal postulates as stated earlier (see section 1.2.4).

In this manner, the domain of ‘medical microbiology’ gradually received a progressive advance-ment through the meaningful researches conducted by several scientists and scholars as enumerated below :

Edwin Klebs (1883) and Frederick Loeffler (1884) : discovered the diphtheria bacillus, corynebacterium diphtheriae ; and showed that it produced its toxins (poisons) in a laboratory flask.

Emil von Behring and Shibasaburo Kitasato : devised an unique technique of producing im-munity to infections caused by C. diphtheriae by injecting the toxins into healthy animals so that an antitoxin**** gets developed.

Shibasaburo Kitasato and Emil von Behring : cultivated (grown) the microorganism respon-sible for causing tetanus (lockjaw), Chlostridium titani ; and Behring prepared the corresponding anti-toxin for the control, prevention, treatment, and management of this fatal disease.

Emil von Behring bagged the Nobel Prize in 1901 in physiology or medicine.

De Salmon and Theobald Smith : proved amply that immunity to a plethora of infectious diseases may be produced quite effectively and efficiently by proper timely innoculation with the killed cultures of the corresponding microorganisms.

Elie Metchnikoff : described for the first time the manner certain specific leukocytes (i.e., white blood cells) were able to ingest (eat up) the disease-producing microorganisms present in the body. He baptized these highly specific defenders and crusaders against bacterial infections known as phagocytes (‘eating cells’), and the phenomenon is termed as phagocytosis.

Metchnikoff’s Theory : Based of the aforesaid explanations Metchnikoff put forward a theory that — ‘the phagocytes were the body’s first and most important line of defense against a variety of infection’.

Paul Ehrlich : Paul Ehrlich (Robert Koch’s brilliant student) put forward two altogether newer concepts with regard to the modus operandi whereby the body aptly destroys microorganisms (bacteria), namely :

(a) Antibody* : The logical explanation of immunity based upon certain antibodies in the blood, and

(b) Chemotherapy** and Antibiotics*** : Both these aspects virtually opened the flood gates to the enormous future developments in combating the growth and destruction of pathogenic bacteria.

Example : Arsphenamine [Salvarsan(R)] : A light yellow organo-metallic compound (powder) containing about 30% Arsenic (As), was formerly used in the treatment of syphilis.

The two decades stretching between 1880–1900 proved to be indeed a golden era for the ‘sci-ence of microbiology’ to step into adolescence from the stage of infancy. In fact, during this specific period many researchers have gainfully identified the causative microorganisms duly responsible for the eruption of a host of infectious human diseases, such as :

Anthrax, Gonorrhea, Typhoid fever, Malaria, Wound infections, Tuberculosis, Cholera, Diph-theria, Tetanus, Meningitis, Gas gangarene, Plague, Dysentery, Syphilis, Whooping cough, and Rocky Mountain spotted fever.

8. Pharmaceutical Microbiology

The remarkable and spectacular breakthroughs accomplished by Pasteur, Koch, Jenner, and a host of others more or less paved the way towards several miraculous discoveries in curing fatal and dreadful human ailments thereby minimising their immense sufferings. Many meaningful and wonder-ful researches also led to the discovery of a good number of causative agents of diseases and altogether newer techniques for diagnosis, which ultimately rendered the diagnosis of these ailments rather rapid and precise.

Examples : (a) Widal Test* — for typhoid fever, and

(b) Wasserman Test** — for syphilis.

Importantly, a plethora of dreadful diseases were duly identified and characterized by the pres-ence of their specific causative microorganisms, such as : Hensen (1874) leprosy (Mycobacterium leprae) ; Neisser (1879) gonorrhea (Neisseria gonorrhoeae) ; Ogston (1881) wound infections (Staphylococcus aureus) ; Nicolaier (1885) tetanus (Clostridium titani) ; Kitasato and Yersin (1894) plague (Yersinia pestis) ; Shiga (1898) dysentry (Shigella dysenteriae) ; Schaudin and Hoffmann (1905) syphilis (Treponema pallidum) ; Bordet and Gengou (1906) whooping cough (Bordetella pertussis) ; Ricketts (1909) rocky mountain spotted fever (Rickettsia ricketsii) ;

Some of the important events that mark the history of pharmaceutical microbiology are enu-merated below in a chronological arrangement :

Antibiotics : Antibiotic refers to a natural or synthetic substance that destroys microorganisms or inhibits their growth. Antibiotics are employed extensively to treat infectious, diseases in humans, animals, and plants. In fact, the terminology ‘antibiotic’ etymologically evidently signifies anything against life. Obviously, in the event when the microorganisms are critically present in a natural medium two situations may arise invariably viz., (a) favouring the growth of bacteria usually termed as ‘symbiosis’ ;* and (b) antagonizing the growth of bacteria normally called as ‘antibiosis’.**

Charles Robert Darwin (1809–1882), a British naturalist) aptly commenced scientific and me-thodical investigative explorations into the fundamental problems of natural selection and struggle amongst the interspecies ; and later on came up with his famous doctrine — ‘Survival of the fittest’. Louis Pasteur (1822–1895) observed for the first time the characteristic antagonistic interrelations prevailing between the microorganisms of different species.

Joubert and Pasteur first observed the critical destruction of cultures of Bacillus anthracis by means of certain air-borne microbes. A follow up by Sirotinin (1888) emphatically proved the antago-nistic action of Bacillus anthracis upon the enteric fever, and Blagoveshchensky (1890) carefully ascer-tained the antagonistic effect of the blue-pus organism on the Bacillus anthracis. It was ultimately the miraculous discovery of Lashchenkov (1909) and Alexander Fleming (1922) who meticulously isolated the enzyme lysozyme***, that was chiefly capable of inhibiting a relatively larger segment of microor-ganisms. Chain, Florey, and co-workers (1929) made the epoch making historical development in the emerging field of antibiotics with the remarkable discovery of wonderful therapeutic and interesting pharmacological properties of the extracts obtained from the cultures of the mold Penicillium notatum that eventually gave rise to the formation of the wonder drug ‘penicillin’.

Specifically the antibiotics are extremely useful in the control, management and treatment of a good number of human infectious diseases but their diversified applications are found to be equally useful in the meticulous curing and controlling of plant and animal diseases as well. Penicillin has been effectively employed in the management and control of pests. Antibiotics, in general, are invariably employed in animal husbandry as ‘feed additive’ to cause enhancement in the fattening of food animals. Food handling and processing industries extensively make use of antibiotics to critically minimise in-evitable spoilage of fish, vegetables, and poultry products. Present day modern scientific researches being conducted across the globe do make use of antibiotics as useful and indispensable tools for the elaborated study of biochemical cellular mechanisms.

Since the discovery of penicillin many more antibiotics came into being as stated under :

Waksman (1944) : Streptomycin — [Streptomyces griseus] — a soil microbe ;

—(1945) : Bacitracin — [Bacillus subtilis] ;

—(1947) : Chloramphenicol (Chloromycetin) — [Streptomyces venezuelae] ;

—(1947) : Polymixin — [Bacillus polymixa] — and various designated polymixins A, B, C, D, and E.

—(1948) : Chlorotetracycline — [Streptomyces aureofaciens] — a broad-spectrum antibiotic.

—(1948) : Neomycin — [a species of Streptomyces] — isolated from soil.

—(1950) : Oxytetracycline — [a strain of Streptomyces].

—(1952) : Erythromycin — [Streptomyces erythreus].

It is, however, pertinent to state here that the ‘antibiotics’ may be broadly classified into nine categories as given below :

[Kar, Ashutosh : Pharmacognosy and Pharmacobiotechnology, New Age International (P) Ltd., Publishers, New Delhi, 2003].

Important Points : The various important points with respect to the development of antibiotics are summarized below :

·        in all approximately 5000 antibiotics have been prepared, characterized, and evaluated for their therapeutic efficacy till date.

·        nearly 1000 antibiotics belonging to only six genera of filamentous fungi i.e., including Cephelosporium and Penicillium have been reported successfully.

·        about 50 antibiotics have been synthesized from two genera and belonging to the class of non-filamentous bacteria.

·        nearly 3000 antibiotics have been prepared from a group of filamentous bacteria i.e., in-cluding streptomyces.

·        approximately 50 antibiotics are at present actively used in therapeutic treatment and veteri-nary medicine around the world.

Importantly, the most common bacteria that invariably attack the humans specifically, and the diseases they cause or organs of the body they attack, are listed as under :

9. Industrial Microbiology

An exponential growth in the ever expanding domain of industrial microbiology commenced logically from the mid of the nineteenth century to the end of the said century. The various vital and important ‘milestones’ in the field of industrial microbiology may be summarized as stated under :

Emil Christian Hansen (1842-1909) : a Dane*, who actually showed up the brilliant and fertile way to the extremely investigative field of industrial fermentations. He meticulously examined and methodically developed the pure culture study of microorganisms and yeasts exclusively utilized in the large-scale manufacture of ‘fermented vinegar’. This simultaneously encouraged as well as prom-ulgated the application of pure cultures termed as ‘starters’ associated with the elaborated study of various fermentation processes.

L. Adametz (1889) : an Austrian, augmented the commercial production of cheese by making use of pure cultures (i.e., starters).

HW Conn (in Connecticut, USA) and H Weigmann (in Germany) (1890–1897) : developed miraculously a host of pure culture starters for the commercial production of butter.

Alcohol Fermentations : Pure culture of yeasts were used to produce alcohol (ethanol) from a variety of fermentable carbohydrates such as : corn, molasses, potatoes, sugar beets, grapes etc., employed throughout the world.

In addition to the above mentioned widely consumed and need based products there are several other highly in-demand industrial products derived exclusively from molds that are being used largely across the globe as detailed under :

10. Emergence of Molecular Biology

Molecular Biology refers to that specific branch of biology dealing with analysis of the struc-ture and development of biological systems vis-a-vis the chemistry and physics of their molecular constituents. Now, with the advent of latest laboratory methodologies and modern experimental tech-niques the prevailing skill, wisdom, and knowledge pertaining to the characteristic features of microor-ganisms accumulated with a tremendous momentum and speed. Based upon the intensive and extensive information(s) with respect to the in-depth biochemical activities of various microorganisms virtually became an ‘open-secret’.

Importantly, a careful and critical examination of the copious volume of accumulated data evi-dently revealed and suggested that there existed quite a lot of similarities amongst the different micro-organisms, whereas the points of dissimilarities revolved essentially around the variations on a major central biochemical pathway. Interestingly, at that point in time there prevailed a distinct world-wide emergent growing recognition between the ensuing unity of the biochemical life processes in micro-organisms and the higher forms of life (including the humans). As a result, it more or less turned out to be definitely much beneficial and advantageous to employ the microorganisms as a befitting tool for deciphering and exploring the basic life phenomena. In order to accomplish the aforesaid aims and objectives the microorganisms do offer invariably a plethora of advantages for this type of research activities, namely :

·        they reproduce (i.e., cultivate) extremely fast,

·        they may be cultured (grown) either in small or large quantum easily, conveniently, and quickly,

·        their growth may be manipulated and monitored in a not-so-difficult manner by means of chemical and physical methods, and

·        their cells may be cleaved and torn apart, and the contents segregated into different fractions of varying particle sizes.

Conclusively, the above cited characteristic features together with certain other vital factors help to render the ‘microorganisms’ an extremely vulnerable and a very convenient research-role-model in pin-pointing and establishing precisely the modus operandi of various life processes that essentially occur with respect to certain particular chemical reactions, besides the specific structural features involved intimately.

In the light of the above statement of facts showing the enormous strengths of microorganisms in the revelation of the intricacies of life processes various scientists and researchers of all disciplines viz., physicists, chemists, geneticists, biologists, and microbiologists not only joined their hands together but also put their intellectual resources and wisdom in a concerted manner to evolve an altogether new discipline christened as molecular biology. According to Professor Luria* molecular biology may be defined as — ‘the programme of interpreting the specific structures and functions of organisms in terms of molecular structure’.

The outcome of the results obtained from the brilliant studies accomplished in the field of mo-lecular biology are numerous, such as :

·        Elucidation of enzyme structure and mode of action,

·        Cellular regulatory mechanisms,

·        Energy metabolism mechanisms,

·        Protein synthesis,

·        Structure of viruses,

·        Functionality of membranes, and

·        Structure and function of nucleic acids.

Significance of Discoveries : The major significance of discoveries with regard to molecular biology may be ascertained by virtue of the following breakthroughs :

·        Fundamental information(s) regarding DNA and genetic processes at the molecular level via bacteria and bacteriophages**, and

·        Many Nobel Prizes bagged due to researches carried out in molecular biology related to various arms of biology.

11. Emergence of Virology

Virology essentially refers to — ‘the study of viruses and viral diseases’.

Preamble : Towards the later part of the nineteenth century Pasteur and his co-workers were vigorously attempting to unfold the precise and exact mechanism of the phenomenon of disease development by examining meticulously a good number of infectious fluids (drawn from patients) for the possible presence of specific disease producing agent(s) by allowing them to pass through filters with a view to retain the bacterial cells. An affirmative conclusion could be reached easily in the event when the filtrates (obtained above) failed to produce any infection, and the presence of the disease producing bacterial agent in the original (infectious) fluid.

The following researchers determined the presence of ‘virus’ in pathological fluids in the fol-lowing chronological order :

Chamberland (1884) : First and foremost developed the specially designed ‘porcelain filters’ that exclusively permitted the passage of fluid but not the microorganisms ; and, therefore, could be used gainfully for the sterilization of liquids. Besides, the application of such devices may also suggest and ascertain if at all ‘infective agents’ smaller in dimensions than the bacteria could exit actually.

Iwanowski (1892) : Repeated the similar sort of test but employed an extract meticulously obtained from the infected tobacco plants, with ‘mosaic* disease’. Iwanowski observed that the clear filtrate was found to be extremely infectious to the healthy tobacco plants.

Beijerinck (1898) : He confirmed Iwanowski’s findings and baptised the contents of the clear filtrate as ‘virus’ (i.e., infectious poisonous agent). He further affirmed that the virus could be propogated strategically within the living host.

Loeffler and Frosch (1998) : They first and foremost demonstrated that the clear filtrate hap-pened to be the main culprit, virus, which had the capability of being transmitted from one infected animal to another. Later on they amply proved that the lymph** obtained from infected animals suffer-ing from ‘foot and mouth disease’, whether it was either filtered or unfiltered, both caused infection in healthy animals almost to the same extent. From the above critical studies one may infer that since animals infected with the filtered lymph served as a source of inoculum*** for the infection of healthy animals thereby suggesting overwhelmingly that the infective filterable agent never was a toxin****, but an agent capable of undergoing multiplication.

FW Twort (1915) : Twort inoculated nutrient agar with smallpox vaccine fluid with a possible expectation that a virulent variant of vaccinia virus could grow up eventually into colonies. In fact, the only colonies which actually showed up on the agar plates were nothing but bacteria that proved to be contaminants in the vaccine lymph. However, these bacterial colonies had undergone a transformation that turned into a ‘glassy watery transparent substance’, which could not be subcultured anymore.

Salient Features of ‘Glassy-Watery Transparent Substance : The various salient features of the glassy-watery transparent substance are as given under :

(1) When a ‘normal bacterial colony’ was contacted even with a trace of the ‘glassy-watery transparent substance’, the normal colony would in turn be transformed right from the point of contact.

(2) Even when the ‘glassy-watery transparent substance’ subjected to a million-fold dilution it affords transformation as well as gets across the porcelain bacteria-proof filters.

(3) By successive passages from glossy to normal colonies it could be feasible to transmit the disease for an indefinite number of times ; however, the specific agent of the disease would neither grow of its own on any medium, nor would it cause the glassy transformation of heat killed microorganisms.

(4) The specific agent may also be stored for more than 6 months at a stretch without any loss in activity whatsoever ; however, it would certainly be deprived of its activity when heated to 60°C for 1 hour.

Twort, in 1915, put forward three logical and possible explanations based on his original discov-eries, namely :

(1) The bacterial disease may represent a stage of life-cycle of the bacterium, wherein the bac-terial cells would be small enough to pass via the porcelain bacteria proof filters, and are also unable to grow on media which actually support the growth of normal microorganisms.

(2) The causative organism (agent) could be a bacterial enzyme that invariably leads to its own production and destruction, and

(3) The organism (agent) could be a virus that ultimately grows and infects the microorganisms.

It is, however, pertinent to state here that the later two probabilities (i.e., ‘1’ and ‘2’ above) gained tremendous recognition and turned out to be the hottest topic of various vigorous investigations inspite of the brief forceful and unavoidable interruptions caused by the World War 1.

F. d’Herelle (1917) : For almost two years the splendid research and observations of Twort remained unnoticed until the investigations of d’ Herelle-an entomologist who incidentally encountered during that period a particular transmissible disease of bacteria while investigating the organisms causing diarrohea in locust. While experimenting with the coccobacilli* d’Herelle observed that the cell-free fil-trates could give rise to ‘glassy’ transformation. Besides, he watched carefully that in the absence of cocobacilli the agent i.e., ‘glassy-watery transparent substance’ failed to grow in any culture media. Interestingly, d’Herelle carried out his research absolutely in an independent manner without the least knowledge about Twort’s findings. His work prominently and emphatically attracted immense and wide-spread attention which ultimately paved the way towards the dawn of a relatively more clear picture of bacterial viruses.

In addition, d’Herelle helped in the discovery of certain earlier preliminary methodologies for the assay** of bacteriophages.*** It has been duly observed that the lysates displayed practically little effect upon the inactivated organisms (bacteria), which fact was further looked into and adequately established that the bacteriophages are nothing but definitive self-producing viruses that are essen-tially parasitic on microorganisms.

Lwoff (1921) : Lwoff further ascertained and proved the fact that bacteria invariably carry bacteriophages without undergoing ‘any sort of clearance’, and it was termed as ‘lysogeny’*.

12. Microorganisms as Geochemical Agents

The mid of the nineteenth century witnessed an ever growing interest in the pivotal role of microorganisms in carrying out not only the various processes related to fermentations but also tackling some of the human diseases. Nevertheless, Pasteur’s articulated contributions on fermentation evidently proved and established that microorganisms in particular may cater as highly specific entities in per-forming a host of chemical transformations.

Winogradsky and Beijerinck legitimately shared the overall merit and credibility for establishing the precise role of microbes in the critical transformations of N and S.

Windogradsky (1856-1953) : He critically examined and observed that there exist a plethora of distinct and discrete categories of microorganisms each of which is invariably characterized by its inherent capability to make use of a specific inorganic energy source.

Examples :

(a) Sulphur Microbes : They oxidize inorganic sulphur containing entities exclusively.

(b) Nitrogen Microbes : They oxidize inorganic nitrogen containing compounds solely.

Interestingly, Winogradsky caused to be seen that there are certain microorganisms which either in association with free living or higher plants may exclusively make use of gaseous nitrogen for the synthesis of the specific cell components.

Hellriegel and Wilfarth (1888) : They showed explicitely that a predominantly mutual and immensely useful symbiosis does exist between bacteria and the leguminous plants particularly.