Bacterial Cell Structure Taxonomy & Classification PDF

Bacterial Cell Structure Taxonomy & Classification (Two Lectures: Second and Third) By Prof. Dr. Zainalabideen A. Al-Abdulla, DTM&H., MRCPI, Ph.D., FRCPath. (U.K.) LEARNING OBJECTIVES You should be able to: 1. Study the structure of both eukaryotic and proka...

Bacterial Cell Structure Taxonomy & Classification (Two Lectures: Second and Third) By Prof. Dr. Zainalabideen A. Al-Abdulla, DTM&H., MRCPI, Ph.D., FRCPath. (U.K.) LEARNING OBJECTIVES You should be able to: 1. Study the structure of both eukaryotic and prokaryotic cells. 2. Learn the structural differences between prokaryotic and eukaryotic cells. 3. Cite the important functions of the studied cellular structures. 4. Study the basis of Taxonomy, and microbial classifications. 5. Study and read about the Five-kingdom and Three-Domain Systems of Classification. 6. Expand knowledge on rRNA subunits & genes. 7. Answer correctly all the 10 MCQ of your book.  Cell Structure 1. Cell wall 2. Cell membrane 3. Cytoplasm 4. Endoplasmic reticulum (rough , smooth) 5. Ribosomes 6. Golgi Complex 7. Lysosomes and Peroxisomes 8. Mitochondria 9. Plastids 10. Cytoskeleton 11. Nucleus 12. Flagella and cilia Typical eukaryotic animal cell Cross section through a yeast cell: The cross section shows the nucleus (N) with nuclear pores (P), mitochondria (M), and vacuole (V). The cytoplasm is surrounded by the cell membrane. The thicker outer portion is the cell wall Typical Prokaryotic cell Cell wall 1. Present in most bacteria vs absent in most eukaryotes (see the exceptions) 2. Algae: Contain cellulose (as plants), eukaryote Fungi : Contain chitin, eukaryote Archaea: No peptidoglycan, in between Prok. & Euk. Mycoplasma: No cell wall, prokaryotic 3. Function: Provides rigidity, strength, and protection; defines shape of bacteria 4. - Gram positive bacteria: Thick peptidoglycan + teichoic acid + lipoteichoic acid - Gram negative bacteria: Thinner peptidoglycan + Lipid macromolecules (outer membrane) Cell membrane 1. Functions: A. Selective permeability B. Active transport functions 2. Composed of proteins + phospholipids 3. Similar structure and function in eukaryotic and prokaryotic 4. Mesosomes: Foldings in cell membrane of bacteria for respiration (vs eukaryotic in mitochondria) Ribosomes Human (40S, 60S, 80S) Bacteria (30S, 50S, 70S) This is important in understanding the selective action of some antimicrobials acting on bacteria Sites for protein synthesis Endoplasmic reticulum A. Rough ER: Ribosomes attached; for protein metabolism B. Smooth ER: No ribosomes attached; for lipid+ carbohydrates metabolism Cytoskeleton Includes microtubules, microfilaments “actin”, intermediate filaments: - Some present in bacteria (microtubules are absent in bacteria) and all present in eukaryotes. - Support shape, cellular division, transport, signaling, and other functions. Nucleus of eukaryotes “Command center” Nucleoplasm Nuclear membrane Nucleic Acids (DNA/RNA) Chromosome Genes Genotype (genome) Nucleolus Note: No nucleus in prokaryotes (e.g. bacteria) Chromosome 1. A single circular and folded chromosome in bacteria (vs linear in eukaryotes; human 23 pairs) 2. Number of genes in bacteria 575-55,000 (vs human 20,000-25,000) 3. Plasmids: Small, circular dsDNA, extra- chromosomal, contain genes, single or multiple, same or different copies (vs no plasmids in eukaryotes) 4. Plastids: Cytoplasmic organelles in some eukaryotes (e.g., algae, plants); for photosynthesis Flagella (single: flagellum) - Thread-like - Protein appendages (3-4 Flagellin twisted threads) - For motility (movement); Bacteria never has cilia - Help classification and identification: - Peritrichous: Around (entire) - Lophotrichous: Tuft (many) uni-polar (one end) - Monotrichous: Single polar - Amphitrichous: Bi-Polar (both ends) - Complex structure when present eukaryotes, e.g. spermatozoa (vs simple structure in bacteria) Salmonella cell showing peritrichous flagella; Flagella Stain Transmission Electron Micrograph of mouse respiratory cilia: 9 + 2 arrangement of microtubules within each cilium; Two single microtubules in the center surrounded by 9 doublet microtubules Pili (Fimbriae): sing. pilus/fimbria - Hair-like on gram negative bacteria mostly - Polymerized protein (pilin), rigid - These organelles are NOT for motility - Arise from the cytoplasm, pass through plasma membrane, cell wall and capsule (if present) - Two types of pili: A. For adherence (attachment) B. Sex pilus for transfer of genetic material from plasmid between bacteria (a donor with a single pilus to a recipient cell; this process is called conjugation) - Pilus is a pathogenic factor Schematic drawing of bacterial conjugation. 1- Donor cell produces pilus. 2- Pilus attaches to recipient cell, brings the two cells together. 3- The mobile plasmid is nicked and a single strand of DNA is then transferred to the recipient cell. 4- Both cells recircularize their plasmids, synthesize second strands, and reproduce pili; both cells are now viable donors. Proteus vulgaris cell, possessing numerous short straight pili and several long, curved flagella. The cells is undergoing binary fission. Glycocalyx (slime layers and capsule) 1. Slime layer (e.g. Pseudomonas): - Not highly organized glycocalyx - Not firmly attached to cell wall (easily detached) - Pathogenic factor: Assists in sliding (gliding) of bacteria, and protects against antimicrobials 2. Capsule(e.g., Haemophilus influenza type-b (Hib): - Highly organized glycocalyx (polysaccharides + lipids + proteins) - Firmly attached to cell wall - Pathogenic factor (also: resists phagocytosis) - Chemical composition helps identification of m.o. Identification of capsule 1. Negative stain: - Bacteria and background: Stained - Capsule: Unstained halo 2. Antibodies reaction with capsular antigens (e.g., capsule swelling test “Quellung Test”; antigenic serotyping) 3. Cultural characteristics: - Capsulated: Smooth, mucoid, and glistening colonies (S-colonies) - Nonencapsulated: Dry and rough colonies (R-colonies) Capsule Stain: Hallow around bacteria Spores (Endospores) - Spore-forming bacteria: e.g. Bacillus, Clostridium - Thick-walled, for survival (not reproduction) - Formation of spores = Sporulation - Contain a copy of the chromosome + cytoplasm surrounded by several thick protein coats - Resistant to heat, cold, drying, chemicals, boiling, and disinfectants - One spore produces one vegetative bacterium by germination in moisture, and with nutrients - Spore staining: Terminal, Sub-terminal, Central types which can be bulging (swelling) or NOT Reproduction of eukaryotic and prokaryotic cells Mitosis/Meiosis vs Binary Fission Binary Fission: One bacterium (parent cell) splits in half after its chromosome has duplicated (DNA replication) to become two daughter cells. Generation time: The time of the binary fission to occur. It varies (10 min. to 24 hours) according to: - Bacterial species (e.g. E coli : 20 min.) - Growth conditions (pH, temperature, nutrients) Binary Fission: DNA replication must occur before the actual splitting (fission) of the parent cell Eukaryotic vs Prokaryotic cells eu = true, karyo = nucleus 1. True nucleus: DNA enclosed by nuclear membrane (vs absent membrane in prokayotics) 2. Eukaryotic size X10 of prokaryotic cells 3. Absence of cell wall in animals (vs present) 4. Presence of complex membrane structures & organelle (ER, Golgi, mitochondria, plastids); (vs absent; contain only cytoplasmic particles as ribosomes/ polyribosomes and stored granules) 5. Ribosomes 80, 60, 40S (vs 70, 50,30S prokaryotes) 6. Mesosomes in bacteria vs mitochondria in eukaryote Bacterial Taxonomy and Classification Taxonomy: The science of classification of living organisms. It consists of THREE areas: 1. Classification 2. Nomenclature 3. Identification Classification Arrangement into taxonomic groups (taxa): Kingdoms or Domains, Divisions or Phyla, Classes, Orders, Families, Genera and species. “KFC OF G” Nomenclature: Giving international names to taxa Identification: Known or unidentified species? ( to speciate). The process is called phenotyping. Microbial Classification - Binomial system of nomenclature (18th century): First: Genus (pl. genera), first letter capital, underline or italicize, e.g., Shigella, or Shigella; genus named also by a single letter ( Shigella = S) Second: Specific epithet; first letter small, underline or italicize (e.g. Shigella dysenteriae, or Shigella dysenteriae; if a single species: “sp.”, more than one species: “spp.” e.g. Shigella spp. Other information about nomenclature - First name + second name = Genus + species - Sub-specific epithet = ssp., e.g., H. influenza ssp. aegyptius - Nickname: e.g. Staphylococcus = Staph. - Bacterial names are named for the disease, e.g. - Vibrio cholerae = cholera Classifications of living organisms 1. FIVE Kingdoms (see below the names) 2. Three-Domain System- based on rRNA differences (by Carl Woese, 1970s): A. TWO domains prokaryotes (Archaea and Bacteria) B. ONE domain Eucarya or Eukarya Five Kingdom System of Classification In 1969, Robert H. Whittaker prosed this classification: 1. Bacteria and archaea are in the Kingdom Prokaryotae (or Monera) 2. Algae and Protozoa are in the Kingdom Protista (Protists) 3. Fungi are in the Kingdom Fungi 4. Plants are in the Kingdom Plantae 5. Animals are in the Kingdom Animalia (including humans) Ribosomal RNA (rRNA) - rRNA sequencing - rRNA has 2 subunits: 1. Small subunit rRNA (SSUrRNA), ONE RNA mole.: a. Bacteria : 16S; coding gene contains 1500 DNA nucleotides (16S rDNA sequence)* b. Eukaryotes: 18S; coding gene contains 2000 nucleotides (18S rDNA sequences)* * Similarities & differences between prokaryotes and eukaryotes are based on rDNA sequences 2. Large subunit rRNA (LSUrRNA)