The document discusses the classification of microorganisms, defining microbiology as the study of organisms too small for the naked eye and categorizing them into prokaryotic and eukaryotic cells. It highlights advancements in microbial classification through electron microscopy, biochemical studies, and nucleic acid sequencing, leading to a revised classification system with three domains: bacteria, archaea, and eucarya. Additional details cover the roles and characteristics of various microorganisms, including bacteria, archaea, fungi, algae, and acellular infectious agents such as viruses, viroids, and prions.

1. Presented By
Sijo A
Ph.D. Research Scholar (Microbiology)
School of Biosciences, MACFAST College
Tiruvalla, Kerala
CLASSIFICATION OF MICROORGANISMS

2. MEMBERS OF THE MICROBIAL WORLD
• Microbiology is defined as the study of organisms and agents too small to be seen clearly by the
unaided eye.
• It primarily focuses on microorganisms, which are typically less than 1 millimeter in diameter.
• Because of their small size, these organisms usually require a microscope for examination.
• However, some microorganisms, especially certain eukaryotic microbes, can be seen without a
microscope.
• Examples of visible microbes include:
Bread molds Filamentous algae

3. Prokaryotic cells
• Derived from Greek: "pro" (before) and "karyon" (nut or kernel).
• Have a simpler morphology.
• Lack a true membrane-bound nucleus.
Eukaryotic cells
• Derived from Greek: "eu" (true) and "karyon" (nut or kernel).
• Have a membrane-enclosed nucleus.
• More complex in structure and usually larger than prokaryotes.
• These differences led to the development of a classification scheme dividing organisms into five kingdoms: Monera,
Protista, Fungi, Plantae and Animalia
• Microorganisms, except for viruses and other acellular infectious agents, are classified within the first three kingdoms.
PROKARYOTIC AND EUKARYOTIC CELLS

4. MICROBIAL CLASSIFICATION
• Recent progress in microbial classification has been made in three key areas:
1. Electron microscopy: Provided detailed insights into the structure of microbial cells.
2. Biochemical and physiological studies: Determined characteristics of many different microorganisms.
3. Nucleic acid and protein sequencing: Enabled comparisons across a wide variety of organisms.
• Carl Woese began comparing ribosomal RNA (rRNA) sequences in the 1970s, revealing:
• Two distinct groups of prokaryotic organisms: Bacteria and Archaea.
• These were previously classified together as Monera in the five-kingdom system.
• Further rRNA studies showed that:
• Protista is not a cohesive taxonomic unit and should be divided into three or more kingdoms.
• Conclusion:
• The five-kingdom system is considered too simplistic.
• Many taxonomists now support a classification system with three domains:
1. Bacteria (true bacteria or eubacteria)
2. Archaea
3. Eucarya (all eukaryotic organisms)

5. • Prokaryotic, usually single-celled organisms.
• Most have cell walls containing peptidoglycan.
• Abundant in soil, water, air, and major inhabitants of human skin, mouth, and intestines.
• Some live in extreme environments, including high temperatures, pH, or salinity.
• Roles of bacteria:
• Some cause diseases.
• Many play beneficial roles:
• Cycling elements in the biosphere.
• Breaking down dead plant and animal material.
• Producing vitamins.
• Cyanobacteria:
• Formerly known as blue-green algae.
• Produce significant amounts of oxygen through photosynthesis.
BACTERIA

6. • Prokaryotes distinguished from Bacteria by unique features.
• Notable differences include unique ribosomal RNA sequences.
• Lack peptidoglycan in their cell walls.
• Possess unique membrane lipids.
• Metabolic characteristics:
• Some have unusual metabolic traits, like methanogens, which generate methane gas.
• Habitat:
• Many archaea thrive in extreme environments:
• High temperatures (thermophiles).
• High salt concentrations (extreme halophiles).
• Pathogenicity:
• No pathogenic archaea have been identified.
ARCHAEA

7. Some archaea live in extreme environments, such as the Morning Glory pool, a hot spring in Yellowstone National Park. The color
differences in the pool result from the different communities of microbes that are able to thrive at various water temperatures.

8. • Diverse group of microorganisms.
• Range from unicellular forms (yeasts) to multicellular forms (molds and mushrooms).
• Molds and mushrooms:
• Multicellular fungi.
• Form thin, threadlike structures called hyphae.
• Absorb nutrients from their environment, including organic molecules used for carbon and energy.
• Beneficial roles of fungi:
• Making bread rise.
• Producing antibiotics.
• Decomposing dead organisms.
• Associating with plant roots to form mycorrhizae, which:
• Transfer nutrients to plant roots.
• Improve plant growth, especially in poor soils.
• Harmful roles of fungi:
• Causing plant diseases (e.g., rusts, powdery mildews, smuts).Causing diseases in humans and other animals.
EUCARYA - FUNGI

9. • Eukaryotic organisms.
• Use chlorophyll for photosynthesis.
• Have rigid cell walls.
• Found in moist environments such as soil and aquatic environments.
• Can be microscopic and unicellular or large and multicellular.
• Some species can grow up to 400 feet in length.
• Multicellular algae can vary in form and complexity.
• Some form colonies.
• Colonies can be simple aggregates of cells or contain specialized cell types, similar to higher life
forms.
ALGAE

10. VIRUS, VIROIDS, PRIONS
Viruses:
• Acellular entities that must invade a host cell to replicate.
• Simplest viruses are composed of proteins and nucleic acids.
• Extremely small—up to 10,000 times smaller than a typical bacterium.
• Cause many animal and plant diseases, including:
• Smallpox, Rabies, Influenza, AIDS, Common cold, Some cancers
• Have caused epidemics that have shaped human history.
Viroids:
• Infectious agents composed only of ribonucleic acid (RNA).
• Cause numerous plant diseases.
Prions:
• Infectious agents composed only of protein.
• Cause a variety of spongiform encephalopathies, including:
• Scrapie disease in sheep
• Mad cow disease

11. Small pox Rabies
Influenza Virus
COVID-19

12. Nipah Virus
Ebola Virus
Dengue fever
Monkey pox
(Mpox)