Classification of microorganisms-MICROBIOLOGY QUICK LEARN

MICROBIOLOGY QUICK LEARN-Classification of microorganisms-basics

1. MICROBIOLOGY QUICK LEARN CLASSIFICATION OF MICROORGANISMS Ms Saajida Sultaana Mahusook

2. Living organisms are diverse whether it is plants, animals or microbes. They play important roles in nature. Arranging these microbes in order or hierarchy based on its similarity or differences ( in any characteristics), makes it easier to know and get access to all the microbes. So it is necessary to classify the organisms. Greek Philosopher Aristotle classified the living things as plants and animals around 2000 years ago. John Ray defined species as similar patterns and genera for the group containing closely related species. Carolous Linnaeus proposed the science of taxonomy- the basic rules for taxonomic categories or taxa, binomial nomenclature.

3. Taxonomy Taxonomy [Greek  taxis,  arrangement, and  nomos ,  law] is defined as the science of biological classification.  T axonomy is orderly arranging organisms under study into groups of larger units.  It consists of  three  interrelated parts namely

4. Levels of Classification (Taxonomic hierarchy) Introduced by Linnaeus The main taxa/ groups in a classification are organized into several descending ranks starting with Kingdom and ending with species. Techniques for identifying or determining taxonomical characters Morphology Physiology and metabolism Ecology Genetic analysis

5. Divisions of Life Kingdom systems of classification -Three-kingdom system  (Ernest Haeckel, 1866) – Plants, animals and Protista to include unicellular organisms. -  Five-kingdom system   (Whittaker, 1960s) - based upon cell type, organization, and the means of nutrient acquisition ( Monera , Protista, Fungi, Plantae, Animalia ) -  Six-kingdom system   - differs from five-kingdom system by dividing prokaryotes into bacteria and archaea (Bacteria, Archaea , Protista, Fungi, Plantae, Animalia ) -  Eight-kingdom system   (Cavalier-Smith) - further division of the protists using rRNA data and grouping organisms into two empires ( Eucaryota and Bacteria) containing a total of eight kingdoms [(Bacteria, Archaea ), ( Archezoa , Protista, Plantae, Chromista , Fungi, Animalia )]

6. Five Kingdom Classification

7. Five Kingdom Classification Proposed by RH Whittaker in 1969. The main criteria of the five kingdom classification  was cellular organization( structure, body), mode of nutritional pattern of organisms. This system places all living things into one of the five basic kingdoms. Monera or Prokaryote Protista Fungi Plantae Animalia

8. THREE DOMAIN SYSTEM P roposed by Carl Woese and Fox, is an evolutionary model of phylogeny based on differences in the sequences of nucleotides in the cell's ribosomal RNAs ( rRNA ), as well as the cell's membrane lipid structure and its sensitivity to antibiotics . Comparing rRNA structure is especially useful. Because rRNA molecules throughout nature carry out the same function, their structure changes very little over time. Therefore similarities and dissimilarities in rRNA nucleotide sequences are a good indication of how related or unrelated different cells and organisms are . The system proposes that a common ancestor cell gave rise to three different cell types, each representing a domain. The three domains are Archaea Bacteria Eukarya

9. The Archaea ( A rchaebacteria ) Archaea  are prokaryotic cells . The cell walls of  Archaea  contain no peptidoglycan . T he   Archaea  have membranes composed of branched hydrocarbon chains (many also containing rings within the hydrocarbon chains) attached to glycerol by ether linkages. Archaea  are not sensitive to some antibiotics that affect the  Bacteria , but are sensitive to some antibiotics that affect the  Eukarya . Archaea  contain rRNA that is unique to the  Archaea   and distinctly different from the rRNA of  Bacteria  and  Eukarya . Archaea  often live in extreme environments and include methanogens, extreme halophiles, and hyperthermophiles .

10. The  Bacteria   (Eubacteria ) Bacteria (also known as eubacteria or "true bacteria") are prokaryotic cells. Their membranes are composed of unbranched fatty acid chains attached to glycerol by ester linkages. The cell walls of  Bacteria contain peptidoglycan. Bacteria  are sensitive to traditional antibacterial antibiotics but are resistant to most antibiotics that affect  Eukarya . Bacteria  contain rRNA that is unique to the  Bacteria  as indicated by the presence molecular regions distinctly different from the rRNA of  Archaea  and  Eukarya . They include pathogenic and non-pathogenic bacteria living in soil, water, etc. Bacteria  include mycoplasmas, cyanobacteria, Gram-positive bacteria, and Gram-negative bacteria.

11. The  Eukarya   (Eukaryotes ) Eukarya   includes eukaryotic cells. Like the  Bacteria , they have membranes composed of straight ( unbranched ) fatty acid chains attached to glycerol by ester linkages. Not all  Eukarya  possess cells with a cell wall, but for those  Eukarya  having a cell wall, that wall contains no peptidoglycan . Cell wall is present in plants and fungi. Eukarya  are resistant to traditional antibacterial antibiotics but are sensitive to most antibiotics that affect eukaryotic cells. Eukarya  contain rRNA that is unique to the  Eukarya  as indicated by the presence molecular regions distinctly different from the rRNA of  Archaea  and  Bacteria . The domain includes Protists (algae and protozoan), Fungi, Plants and animals.

12. Reference: Microbiology by Professor  Dushyant Kumar Sharma https ://nptel.ac.in/courses/102103015/34 https ://bio.libretexts.org/Bookshelves/Microbiology/Book%3A_Microbiology_(Kaiser)/Unit_1%3A_Introduction_to_Microbiology_and_Prokaryotic_Cell_Anatomy/1%3A_Fundamentals_of_Microbiology/1.3%3A_Classification_-_ The_Three_Domain_System THANK YOU