General Microbiology Lecture 3, October University, Fall 2024 PDF

Department of Microbiology and Immunology General Microbiology and Microbial Genetics (PHM211) Fall 2024 Lecture 3 ▪ Prokaryotic microbes (Bacterial cell structure - II) References 1. K...

Department of Microbiology and Immunology General Microbiology and Microbial Genetics (PHM211) Fall 2024 Lecture 3 ▪ Prokaryotic microbes (Bacterial cell structure - II) References 1. Kathleen P Talaro_ Barry Chess - Foundations in microbiology _ basic principles (2012, McGraw-Hill ) 2. Paul G. Engelkirk, Janet Duben-Engelkirk - Burton’s Microbiology for the Health Sciences (2014, Wolters Kluwer Health) 3. Pommerville, J. C. - Alcamo's Fundamentals of Microbiology (2010, Jones & Bartlett Learning) 4. Michael T. Madigan, John M. Martinko, David Stahl, David P. Clark-Brock Biology of Microorganisms (13th Edition) -Benjamin Cummings (2010) 5. Stuart Hogg-Essential Microbiology-Wiley-Blackwell (2013) 6. Gerard J Tortora_ Berdell R Funke_ Christine L Case-My microbiology place CD-ROM [to accompany] Microbiology_ an introduction, 10th ed. [by] Tortora, Funke, Case-Benjamin Cummings (2010) 7. Joanne Willey, Linda Sherwood, Chris Woolverton-Prescott's Principles of Microbiology -McGraw-Hill Science_Engineering_Math (2008) 2 Lecture Lecture1 Learning 3 OutlineOutcomes ▪ By the end of the lecture, students should be able to demonstrate knowledge of: Prokaryotic microbes A. Bacteria II. Bacterial cell structure b. Cell envelope 2. Cell wall c. External structures 1. Glycocalyx 2. Flagella 3. Axial filaments 4. Fimbriae and Pilli 3 Lecture Learning1 Learning OutcomesOutcomes Demonstrate a comprehensive understanding of microbial diversity, categorizing microorganisms based on their phenotypic and metabolic characteristics. 4 I. Prokaryotes Which of the following are considered internal structures of bacterial cell? A. Cell wall B,C,D B. Nucleoid C. Ribosomes D. Endospores E. Capsule F. Pili 5 I. Prokaryotes Prokaryotic Microbes A. Bacteria Bacterial cell structure – part II 6  I. Prokaryotic Microbes A. Bacteria Bacterial cell structure a. Cytoplasm I. Internal d. Inclusion bodies ` b. Genetic material e. endospores Cell structures c. Ribosomes Bacterial II. Cell a. Cell membrane ` Envelope b. Cell wall ` a. Appendages (cell extensions) III. External 1. Flagella structures 2. Axial`filaments 3. Fimbriae and Pilli b. Glycocalyx 7 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall (A) Glycan strand ▪ A complex semi-rigid layer that lies just outside the plasma Glycosidic (carbohydrate membrane. bond backbone) 1. Structure: ▪ The cell wall is composed of peptidoglycan (murein): a mesh-like polymer formed of glycan strands that are cross- linked by peptides.  Components of peptidoglycan: A. Carbohydrate backbone (glycan=polysaccharide): - Chains of alternating amino sugars linked by glycosidic bonds: (B) Tetrapeptide o N-acetylglucosamine (NAG) side chain (peptide stem) o N-acetylmuramic acid (NAM) (C) Peptide cross-bridges (interpeptide bridge) B. Tetrapeptide side chains (four amino acids) attached to NAMs in the backbone. Peptidoglycan Structure C. Peptide cross-bridges, consisting of a short chain of 8 amino acids. I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Peptidoglycan Structure 9 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall 2. Functions ▪ It helps determine the shape of the bacterial cell. ▪ It acts as an exoskeleton that maintains the integrity of the cell and protects it from “osmotic lysis”. 3. Clinical importance ▪ The chemical composition of the cell wall is used to differentiate major types of bacteria. Osmotic lysis in the absence of cell walls N.B. Since the cytoplasm contains high concentrations of dissolved substances, bacteria live in a hypotonic environment (i.e. more dilute than their own cytoplasm) will have a natural tendency for water to flow into the cell. In the absence of the cell wall this will cause filling and bursting of the cell in a process called “lysis”. Since the cell wall is required for bacterial survival, but is absent in humans, several antibiotics (e.g; penicillin) stop bacterial infections by interfering with cell wall synthesis, while having no effect on human cell. Penicillin interferes with the final linking of the peptidoglycan rows by peptide cross-bridges 10 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Types of bacterial cell wall: ▪ Long before the detailed anatomy of bacteria was known, a Danish physician named “Hans Christian Gram” developed a staining technique, “the Gram stain” that consisted of timed, sequential applications of different dyes and reagents. ▪ The Gram stain classifies bacteria into different groups: A. Gram-positive: bacteria that stain purple. B. Gram-negative: bacteria that stain red. ▪ The different results in the Gram stain are due to: 1. Differences in the structure of the cell wall. 2. How it reacts to the series of reagents applied to the cells. As Gram-positive bacteria retain the primary dye (crystal violet), while Gram-negative bacteria don’t. 11 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Types of bacterial cell wall: A. Cell wall of Gram-positive bacteria - Multiple peptidoglycan layers (more resistant to osmotic lysis) - It contains acidic polysaccharides: (1) Teichoic acid: attached to NAMs of the peptidoglycan. Functions of teichoic acid: They contain phosphate groups, which impart an overall negative charge to the cell surface. It may be responsible for regulating cation movement to the cell. (2) Lipoteichoic acid: structurally similar to teichoic acid but attached to plasma membrane lipids. (3) Periplasmic space: very small area between inner membrane (plasma membrane) and peptidoglycan, filled with the periplasm that contains enzymes and transport proteins. 12 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Types of bacterial cell wall: A. Cell wall of Gram-positive bacteria 6 Label the figure 1. Cell membrane 2. Cell wall (peptidoglycan) 3. Phospholipid 4. Peripheral protein 5. Lipoteichoic acid 6. Teichoic acid 13 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Types of bacterial cell wall: B. Cell wall of Gram-negative bacteria ▪ Single peptidoglycan layer (higher flexibility and sensitivity to lysis). ▪ No teichoic acid. ▪ Large periplasmic space: above and below the peptidoglycan layer. ▪ It contains an “outer membrane”. 14 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Types of bacterial cell wall: B. Cell wall of Gram-negative bacteria The Outer Membrane (1) The inner half of the outer membrane contains phospholipids similar to the cell membrane anchored to the peptidoglycan by “Lipoproteins”. (2) The outer half is composed of: (a) Lipopolysaccharide (LPS): ▪ On cell death, the cell disintegrates and LPS is released and represents a toxin called “endotoxin” that causes fever and shock reactions (endotoxic shock). ▪ It contributes to negative charge on cell surface. (b) Porins:  Proteins that form pores in the outer membrane through which small molecules pass into the periplasmic space. (3) Functions of outer membrane: ▪ Its strong negative (-ve) charge is an important factor in evading phagocytosis. ▪ The outer membrane also provides a barrier to certain antibiotics, digestive enzymes such as lysozyme. 15 ▪ Act as endotoxin. I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Types of bacterial cell wall: B. Cell wall of Gram-negative bacteria The Outer Membrane 16 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Types of bacterial cell wall: B. Cell wall of Gram-negative bacteria Label the figure 1. Cell membrane 2. Periplasm 3. Outer membrane 4. Phospholipid 5. Peptidoglycan 6. Lipoprotein 7. Protein 8. Lipopolysaccharide (LPS) 9. Porins 17 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Gram-negative bacteria have a more complex cell wall structure with an outer membrane that can be more selective in what it allows to pass through. This can Types of bacterial cell wall: make Gram-negative bacteria more resistant to certain antibiotics and detergents that easily penetrate the simpler cell wall of Gram-positive bacteria. 18 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Comparison between cell wall structures of Types of bacterial cell wall: Gram-positive and Gram-negative bacteria Character Gram-positive Gram-negative Overall thickness Peptidoglycan Teichoic acid Lipopolysaccharide Outer membrane Permeability to molecules 19 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Types of bacterial cell wall: Comparison between cell wall structures of Gram-positive and Gram-negative bacteria Character Gram-positive Gram-negative Overall thickness Thicker Thinner More than one Peptidoglycan One layer layer Teichoic acid Present Absent Lipopolysaccharide Absent Present Outer membrane No Yes Permeability to More Less permeable molecules permeable 20 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Layers of the cell envelope in Gram positive and Gram-negative bacteria 1. Cell membrane 1. Cell membrane 2. Cell wall 2. Cell Wall ▪ Peptidoglycan ▪ Peptidoglycan 21 ▪ Outer membrane I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Layers of the cell envelope in Gram positive and Gram-negative bacteria 22 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure II. Cell envelope 2. Cell wall Types of bacterial cell wall: C. Cell wall-deficient bacteria (1) Some bacteria called “Mycoplasmas” naturally lack a cell wall. ▪ The mycoplasma cell membrane contains sterols that make it resistant to lysis. ▪ Due to lack of cell wall, Mycoplasmas show pleomorphism. They range in shape from filamentous to coccus or doughnut-shaped. Mycoplasmas (2) Some bacteria that have a cell wall can lose it during part of their life cycle. ▪ These wall-deficient forms are referred to as L-forms. ▪ Induction of L-forms: (a) Natural: mutations in the wall-forming genes (b) Artificial: induced by treatment with a chemical that disrupts the cell wall such as: - Lysozyme: an enzyme that attacks peptidoglycan by hydrolyzing the bond that connects NAG with NAM. L-form Bacteria - Penicillin: antibiotic that inhibits the enzyme transpeptidase, which is 23 responsible for making the cross-links between peptidoglycan chains.  I. Prokaryotic Microbes A. Bacteria Bacterial cell structure a. Cytoplasm I. Internal d. Inclusion bodies ` b. Genetic material e. endospores Cell structures c. Ribosomes Bacterial II. Cell a. Cell membrane ` Envelope b. Cell wall ` a. Glycocalyx III. External b. Appendages (cell extensions) ` 1. Flagella structures 2. Axial filaments 3. Fimbriae and Pilli 24 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure III. External Structures 1. Glycocalyx ▪ Definition: ▪ Many prokaryotes secrete on their surface a substance called Glycocalyx is the substance that surrounds the cell (glyco = "sweet";' calyx = "coat“; glycocalyx = “sugar coat”) ▪ Structure: ▪ Glycocalyx is composed of polysaccharide, polypeptide, or both. ▪ Types: Glycocalyces differ among bacteria in thickness, organization, and chemical composition. a. If the glycocalyx is organized and firmly attached to the cell wall, then it is described as a capsule. b. If the glycocalyx is unorganized and only loosely attached to the cell wall, then it is described as a slime layer. 25 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure III. External Structures 1. Glycocalyx Phagocytosis blocked by capsule ▪ Functions 1. It protects cells from desiccation (extreme dryness): because of its high-water content. Capsule around the bacterium 2. It allows cells to attach to surfaces and form biofilms: ▪ Attachment to host cells: e.g; the thick, white plaque that forms on teeth. Phagocyte ▪ Attachment to nonliving surfaces: e.g; plastic catheters, intrauterine devices, and metal pacemakers. 3. It protects cells from phagocytosis by white blood cells (antiphagocytic role): A capsular coating blocks the mechanisms that phagocytes use to attach to and engulf bacteria. 26 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure III. External Structures 2. Flagella ▪ Definition: ▪ Flagella (sing., flagellum = whip) are thread-like, long protein appendages that enable bacteria to move. ▪ Types: ▪ Bacteria that lack flagella are called atrichous bacteria. ▪ If present, flagella are classified according to their arrangement on the cell surface into two types: (1) Polar flagella are attached at one or both ends of the cell, polar flagella are subdivided into: (a) Monotrichous flagella: with a single flagellum (b) Lophotrichous flagella : with small bunches or tufts of flagella emerging from the same site (c) Amphitrichous flagella: with flagella at both poles of the cell. (2) Peritrichous flagella are dispersed randomly over the entire surface of the cell 27 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure III. External Structures 2. Flagella Structure ▪ Each flagellum is a hollow cylindrical “filament” made of a protein called flagellin, attached via a “hook” to “a basal body”, which secures it to the cell wall and plasma membrane. ▪ Functions ▪ Flagella are responsible for motility (the ability of an organism to move by itself). ▪ Flagellated bacteria are motile ▪ Non-flagellated bacteria are nonmotile ▪ Motility enables a bacterium to move toward a favorable environment or away from an adverse one in response to several stimuli, this process is called taxis. Such stimuli include: o Chemicals (chemotaxis) o Light (phototaxis) o Air (aerotaxis) 28 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure III. External Structures 2. Flagella 29 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure III. External Structures 3. Axial Filaments ▪ Also called: “endoflagella” and “periplasmic flagella”. ▪ The axial filament is an internal flagellum that coils around the cell while enclosed in the space between the outer membrane and the cell wall of corkscrew- shaped bacteria called spirochetes. ▪ Function cytoplasm - The rotation of the filaments causes the cells to rotate like a corkscrew. - This enables spirochetes to travel with ease through highly viscous media like mucus and connective tissue. Spirochetes Corkscrew-like motion Corkscrew 30 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure III. External Structures 3. Axial Filaments https://youtu.be/cXYfT5hSLoQ?t=53 31 I. Prokaryotic Microbes A. Bacteria Bacterial cell structure III. External Structures 4. Fimbriae and pili Definition ▪ Hair-like appendages Hair-like that are shorter, straighter, and thinner than flagella. Hair-like Fimbriae and Pilli I. Prokaryotic Microbes A. Bacteria Bacterial cell structure III. External Structures 4. Fimbriae and pili a. Fimbriae (singular: fimbria) ▪ They can occur with any number at the poles of the cell or distributed over the entire surface. ▪ Functions: Fimbriae have a tendency to adhere to each other and to surfaces. They are involved in attachment to host cells (colonization) and nonliving surfaces (biofilms). I. Prokaryotic Microbes A. Bacteria Bacterial cell structure III. External Structures 4. Fimbriae and pili b. Pili (singular: pilus) They are longer than fimbriae and only one or a few pili are present on the surface of a cell ▪ They are made of a special protein called pilin. ▪ Functions 1. They bring bacteria together allowing DNA transfer from one cell to another, a process called conjugation (such pili are called: Sex pili). 2. They allow cells to slide over moist surfaces, this type of motility is called twitching motility. https://youtu.be/yGMSQNBDq48 I. Prokaryotic Microbes Prokaryotes versus Eukaryotes Character Prokaryotes Eukaryotes Size Nucleus DNA Structure Organelles Ribosome Cell wall Cell membrane Cell division Reproduction Examples I. Prokaryotic Microbes Prokaryotes versus Eukaryotes Character Prokaryotes Eukaryotes Size Smaller Larger Nucleus No nuclear membrane True nucleus, with nuclear membrane DNA Single, circular Chromosome Multiple linear chromosomes Structure No Histones DNA is complexed with histones. Present (endoplasmic reticulum, Organelles Absent mitochondria, Golgi bodies, lysosomes) some have chloroplasts 70S 80S Ribosome Smaller than eukaryotic ribosome Larger than prokaryotic ribosome Present Present in fungi, algae and plants Cell wall Formed of peptidoglycan Formed of chitin (fungi) or cellulose Cell No sterols (excep; Mycoplasma) Contains Sterols membrane Cell division Binary fission Mitosis and meiosis Reproduction Asexual Sexual and Asexual Fungi, protozoa, algae, plants and Examples Bacteria and Archaea animals Faculty of Pharmacy