Introduction to Microbiology
Microbiology is the branch of science that studies microorganisms. These are extremely small living organisms that cannot be seen with the naked eye and require a microscope for observation. Microorganisms can be unicellular, multicellular, or acellular in nature.
Unicellular organisms include cocci, bacilli, vibrios and spirilla. Multicellular organisms include filamentous and colonial organisms such as fungi, protozoa, cyanobacteria and bacteria. Acellular organisms include viruses and prions, which do not have a true cellular structure.
Like all living organisms, microbes need nutrients and energy for growth, survival and reproduction. Many microorganisms are useful to humans—for example, in food production, industry and medicine—while some cause diseases.
Branches of Microbiology
Based on Taxonomy
- Bacteriology – Study of bacteria.
- Immunology – Study of the immune system and host–pathogen interactions.
- Mycology – Study of fungi.
- Nematology – Study of nematodes.
- Parasitology – Study of parasites.
- Phycology – Study of algae.
- Protozoology – Study of protozoa.
- Virology – Study of viruses.
Based on Type of Research
- Astromicrobiology – Study of the origin of life and search for life beyond Earth.
- Evolutionary microbiology – Study of microbial evolution and diversity.
- Microbial cytology – Study of microscopic structure of microorganisms.
- Microbial physiology – Study of microbial metabolism, cell structure and growth.
- Microbial ecology – Study of microbes and their environment.
- Microbial genetics – Study of gene organization and regulation in microbes.
- Molecular microbiology – Study of molecular processes in microbes.
- Nano microbiology – Study of microorganisms at nanoscale.
- Microbial taxonomy – Classification and naming of microbes.
- Microbial systematics – Study of diversity and genetic relationships of microbes.
- Cellular microbiology – Combination of microbiology and cell biology.
- Generation microbiology – Study of microbes with characteristics identical to their parents.
Applied Microbiology
- Medical microbiology – Study of disease-causing microbes in humans.
- Pharmaceutical microbiology – Study of microbes used in producing antibiotics, enzymes, vaccines and also those causing contamination in pharmaceuticals.
- Industrial microbiology – Use of microbes in industrial processes such as fermentation and wastewater treatment.
- Food and Dairy microbiology – Study of food spoilage organisms and foodborne pathogens.
- Agricultural microbiology – Study of microbes that influence plants and soil.
- Veterinary microbiology – Study of microbes causing diseases in animals.
- Environmental microbiology – Study of microbial diversity and activity in natural environments.
- Geomicrobiology – Study of interactions between microbes and geological materials.
- Bioremediation – Use of microbes to clean polluted environments.
- Aquatic microbiology – Study of water microorganisms.
- Aeromicrobiology – Study of airborne microorganisms.
Major Divisions of the Microbial World
Earlier, all living organisms were grouped into plant and animal kingdoms. Later, scientists introduced additional kingdoms to better classify microorganisms.
- Kingdom Monera – Prokaryotes such as bacteria, cyanobacteria and archaea.
- Kingdom Protista – Protozoa and algae.
- Kingdom Fungi – Yeasts, molds and mushrooms.
Over time, classification systems evolved:
- Five kingdom classification (Whittaker, 1960) – Monera, Protista, Fungi, Plantae, Animalia.
- Three domain system (Woese, 1977) – Archaea, Bacteria, Eukaryota based on 16S rRNA similarity.
- Six kingdom system – Archaea, Bacteria, Protista, Fungi, Plantae, Animalia.
Comparison of Major Groups
| Feature | Monera | Protista | Fungi |
|---|---|---|---|
| Type | Prokaryotes | Eukaryotes | Eukaryotes |
| Nutrition | Absorption, chemosynthesis, photosynthesis | Photosynthesis, absorption, ingestion | Heterotrophic, saprophytic, parasitic |
| Metabolism | Aerobic/anaerobic | Usually aerobic | Aerobic |
| Reproduction | Asexual (binary fission) | Asexual and sexual | Asexual and sexual |
| Motility | Motile or non-motile | Motile via cilia, flagella, pseudopodia | Usually non-motile |
| Organization | Unicellular/filamentous | Uni & multicellular | Uni (yeast) & multicellular |
| Examples | Bacteria | Protozoa, algae | Fungi |
Relationship Among Microbial Divisions
Relationships between microbial groups are studied using phylogenetic trees based on genetic similarity, especially 16S rRNA.
- A rooted phylogenetic tree shows common ancestors and branching patterns.
- An unrooted tree shows relationships without specifying a common ancestor.
- LUCA (Last Universal Common Ancestor) is considered the starting point from which three major domains—Archaea, Bacteria and Eukaryotes—diverged.
- Archaea and Eukaryotes share a closer evolutionary relationship than Bacteria.
- Further branching shows different microbial groups like gram-positive bacteria, spirochetes, proteobacteria and others.
Key Points
- Microbiology studies organisms too small to be seen without a microscope.
- Microbes include bacteria, fungi, viruses, protozoa, algae and prions.
- They play essential roles in health, environment, food, agriculture and industry.
- Modern classification systems are based on genetic similarity, especially rRNA.
- Understanding relationships helps track evolution and diversity of microorganisms.
Detailed Notes:
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