The period between 1860 and 1919 may be aptly called the first Golden Age of Microbiology. The “age” was preceded by a discovery era when Anton van Leeuwenhoek proclaimed to be the discoverer of the microbial world, discovered around 1676 tiny microbes he called animalcules. He found them in first rainwater, pond water, teeth cavities, and many other specimens. He deposited his sketches of the rod, spherical and spiral forms of “animalcules” which we now know as bacteria to Royal Society of London communications. Francesco Redi and others around the 1600s had a belief in spontaneous generation or abiogenesis doctrine whereby living beings were claimed to be originated from nonliving matter. An example was maggots originating from decaying meat kept in open jars. Subsequently, John Needham discovered animalcules in mutton. However, Lazzaro Spallanzani disproved the previous doctrine in which boiled samples in heated glass sealed jar did not show any animalcule and this finding was extended by Nicholas Appert who could preserve soups, etc. by heating in thick champagne bottles.
In 1859 Louis Pasteur completely discounted spontaneous generation theory and brought out a new theory that microbes are the agents that bring about the chemical changes. His main contributions were as follows: chemical changes like fermentation from the vital activities of yeasts and bacteria, a demonstration that air contains micro-organisms, the discovery of anaerobic life and terms aerobic and anaerobic, and most important discovery of causes of cholera and silkworm disease and immunity in sheep against anthrax. Pasteur also proposed the germ theory in 1862 that germs cause infections. He used swan-necked flasks for his inventions. His specially designed curvature of the flasks prevented microbes to reach the broth inside the flasks and there was no growth. Once the neck was broken off, the broth developed bacterial growth. Robert Koch was a pioneer in identifying the germs outside the infected animals, particularly anthrax, in pure culture in 1867. He developed a series of procedures – Koch’s postulates, by which a specific organism could be related to a specific disease.
The postulates demonstrate; same organisms are causative agents for a disease, the organisms can be isolated from infected animals in pure cultures, Organisms from the pure culture upon inoculation can initiate disease symptoms in healthy animals, and the same organisms can be isolated and re-cultivated from the infected animals. He discovered the gelatinized solidified media. Presently, we have Molecular postulates to define what Koch was observed. This suggests that there are virulence genes present in pathogenic but not in non-pathogenic bacterial strain, and introducing the virulence gene in non-pathogenic strain enable pathogenic phenotype to express, for a disease manifestation the virulence genes must express and the host’s immune system should produce be in a position to respond to the product(s) of virulence genes. S. Winogradsky and M. Beijerinck discovered a remarkable diversity of chemoautotrophic bacteria and numerous biochemical pathways associated with them.
World War I and II marked an end to the 1st Golden Age. While most of the early twentieth century was devoted to biochemistry applied in Microbiology, in the second Golden Age (1941-1970), mainly the discipline of genetics influenced Microbiology. Beadle and Tatum (1941) isolated biochemical mutants in Neurospora, Delbrück and Luria mutated bacteria for viral resistance, and soon afterward genetic transfer was demonstrated in bacteria. In 1944 Avery and co-workers discovered the chemical basis of genetic transfer and the molecule was given a term, deoxyribonucleic acid (DNA). The era of molecular biology began from the discovery of DNA by J.D. Watson and F.H.C. Crick in 1953. The third Golden Age of Microbiology is the current. Among many milestones, discoveries is the modern classification of microbes which reflects the phylogenic and evolutionary positions rather than the structural and/or biochemical features used in the classical taxonomy.
In 1735 Linnaeus classification of two Kingdoms – Animalia and Vegetabilia did not consider microorganisms, in 1866, Haeckel’s three Kingdom system – Animalia, Plantae, and Protista, in 1925, Chatton’s two groups – Eukaryote and Prokaryote, and in 1938, Copeland’s 4 Kingdoms – Animalia, Plantae, Protista, and Monera included the eukaryotic (fungi, etc) and prokaryotic microorganisms. But the revolution in the classification system came from Whittaker’s five Kingdom systems – Animalia, Plantae, Fungi, Protista, and Monera. Later, Carl Woese’s rRNA sequence homology-based classification brought forward the three-domain system of the organisms – Bacteria, Archaea, and Eukarya, including Fungi, Animals, and Plants. The Bergey’s Manual of Systematic Bacteriology also uses the term Kingdom instead of Domain for Archaea (Kingdom I-Archaeota) and Bacteria (Kingdom II-Bacteria). Based on the shape and overall morphology bacteria can be classified as Micrococcus, Diplococcus, Staphylococcus, Streptococcus, Padiococcus, Sarcina, (spheres) Bacillus, Corynebacterium, Vibrio, Spirillum (Straight or curved Rods), Atrichous (without flagella), Monotrichous (one flagellum), Cephalotrichous (many flagella at one end), Amphitrichous (one flagellum at each end), and Lophotrichous (group of flagella at each end). In naming a microorganism, like others, the genus name precedes species epithet. A genus with capitalized and species names in lower case, in the beginning, should be completely spelled in italics. Later, the genus name but not species epithet should be abbreviated.
Define the following terms
- Animalcule: A microscopic or minute organism, such as an amoeba or paramecium, is usually considered to be an animal.
- Antibiotic: Compounds produced from a micro-organism and kill of stop growth of other micro-organisms.
- Archaea: A domain of single-celled prokaryotes genetically distinct from bacteria, often thriving in extreme environmental conditions.
- Bacillus: Rod-shaped, spore-forming, aerobic bacteria of the genus Bacillus often occur in chains.
- Bacteria: Unicellular prokaryotic microscopic organisms with the incipient nucleus.
- Bacteriology: A branch of biological science dealing with the study of bacteria.
- Biotechnology; application or exploitation of an organism for human welfare, the current definition includes doing business using or exploiting an organism.
- Bioterrorism: deliberate and unauthorized private use of biological agents to harm or frighten the people of a state or society, and is related to military use.
- Colony: cell aggregate.
- Eukarya: A domain of organisms whose cells have a true nucleus bounded by a nuclear membrane within which lie the chromosomes; eukaryotic cells also contain many membrane-bound organelles in which cellular functions are performed.
- Eukaryotic: Organisms belonging to domain Eukarya includes higher plants, animals, fungi, algae, etc. which have true nuclei and organelles.
- Germ: A pathogenic microorganism that can cause disease.
- Germ theory: the theory that infectious diseases are due to the agency of germs or microorganisms is based on Koch’s postulates.
- Immunology: A branch of biological science that deals with the study of the immune system of an animal related to defense against disease-causing microorganisms.
- Koch’s postulates: The organisms should be constantly present in diseased animals and not healthy ones, the organisms must be cultivated in culture media when such a culture is inoculated it should initiate disease characteristics, the organisms should be reisolated and cultured again in media.
- Miasma: noxious exhalations from putrescent organic matter; poisonous effluvia or germs polluting the atmosphere.
- Microbe: Microscopic organisms like bacteria, certain algae, and fungi, protozoans, and viruses.
- Microbiology: A branch of biological science that deals with the study of micro-organisms.
- Microorganism: An organism that is microscopic or submicroscopic, which means it is too small to be seen by the unaided human eye.
- Mycology: A branch of biological science that deals with the study of fungi and fungi-like organisms like slime molds.
- Pathogen: Infectious organisms such as bacteria, fungi, and viruses.
- Phycology: A branch of biological science that deals with the study of algae including prokaryotic blue-green algae.
- Phylogeny: The evolutionary development and history of a species or higher taxonomic grouping of organisms.
- Prokaryotic: organisms lacking a true nucleus.
- Protozoology: A branch of biological science that deals with the study of protozoan including chlorophyll-containing euglena.
- Spontaneous generation: In petrifying food the nonliving particles spontaneously generated the life forms including bacteria.
- Virology: A branch of biological science that deals with the study of viruses.
Sources
Madigan, M.T., Martinko, J.M. & Parker, J. (2000). Brock Biology of Microorganisms, 9th Edition. Upper Saddle River (NJ): Prentice-Hall, Inc.
Pommerville, J. C. (2007). Alcamo’s Fundamentals of Microbiology, 8th Edition. Sudbury: Jones and Bartlett.