Bacterial Cell Structure PDF

VPRP096 Introduction to Microbiology: Bacterial structure Dr. Ricardo Gutiérrez, Microbl., MSc, Ph.D. Assistant Professor [email protected] Spring semester, 2024 Bacterial cell structure Bacteria are EVERYWHERE (omnipresence) Essential for the existence of all life on Earth Ubiquitous and nu...

VPRP096 Introduction to Microbiology: Bacterial structure Dr. Ricardo Gutiérrez, Microbl., MSc, Ph.D. Assistant Professor [email protected] Spring semester, 2024 Bacterial cell structure Bacteria are EVERYWHERE (omnipresence) Essential for the existence of all life on Earth Ubiquitous and numerous Beneficial >>> Pathogenic (video in Canvas) Very small (invisible to the naked eye) Bacterial cell structure Diverse morphologies & arrangements Bacterial cell structure Diverse morphologies Bacterial cell structure Bacterial cell structure Sizes In general, bacterial sizes (diameter) range from 1 µm to 5 µm (true range: 0.1 µm – 2.0 cm) Bacterial cell structure Sizes Bacteria in the tip of a pencil under scanner electron microscopy (SEM) Thiomargarita magnifica: the largest bacterium known (2.0 cm long) Habitat: rotting leaves sunken in the mangroves of Guadeloupe (Caribbean) Bacterial cell structure Cell structure Prokaryotes (pro – before; karyote – nucleus) Unicellular organisms Lack of membranous organelles and true nucleus Bacterial cell structure Eukaryote vs prokaryote cells Bacterial cell structure All bacteria have: Cytoplasm Ribosomes Nucleoid (DNA) Plasma membrane Complex and rigid cell wall* Some bacteria have: Capsule Flagella Pili/fimbriae Plasmids Some bacteria can produce: Endospores *exception indicator Bacterial cell structure Cytoplasm: Jelly-like aqueous solution (cytosol) Cytoplasm Functions: Facilitate major chemical reactions of the cell Contains: nucleoid (DNA) and ribosomes Bacterial cell structure Nucleoid Nucleoid (DNA): The bacterial chromosome Double-stranded DNA Mostly single* (haploid) and circular* Function Contains the essential genes for the life of the bacteria (core-genome) *exception indicator Bacterial cell structure Plasmid Plasmids: Circular DNA molecule Double-stranded DNA Some are conjugative (able to be passed to other bacteria) Contains additional genes, not essential Functions: Provide virulence factors (genes) Antibiotic resistance (genes) & other genes… Bacterial cell structure Ribosomes: Ribosomes The cellular protein factory Composed by proteins & rRNA Two subunits = large (50S) and small (30S) Conserved genetic code Applications = therapy + phylogeny Bacterial cell structure Bacterial envelope: 1. 2. 3. 4. Bacterial envelope 4 2 3 1 Cytoplasmic or plasma membrane Membrane-associated proteins Cell wall (peptidoglycan layer) Allows the characterization of the two main groups of bacteria Bacterial cell structure 1. Cytoplasmic membrane Flexible structures Layer composed of phospholipids and proteins No sterols (present in eukaryotic cells) Outer faces are hydrophilic, interior is hydrophobic Bacterial cell structure 2. Membrane-associated proteins OUTSIDE Stabilization of membrane Transport of molecules Electron transport for bacterial respiration Enzymes Bacterial cell structure 3. Cell wall (peptidoglycan layer) Peptidoglycan = chain of alternating subunits of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) crosslinked with short peptides Functions Protection against mechanical damage and osmotic lysis Non-selective transport Differences in structure and chemical composition ~ pathogenicity and staining properties Bacterial cell structure 4. Allows the characterization of the two main groups of bacteria Bacterial cell structure 4. Allows the characterization of the two main groups of bacteria Gram-staining technique Bacterial cell structure Gram Staining Pink: Gram-Negative Purple: Gram-Positive Bacterial cell structure Bacterial envelope: Outer membrane Only in Gram-negative bacteria Periplasmic space Contains: Lipopolysaccharide: a strong immunogenic molecule (called endotoxin) Porins: protein channels that allow small hydrophilic molecules Transporter proteins: enable transport of larger nutrients Bacterial cell structure Alternative structural bacterial envelopes Mycobacteria Bacterial envelope contains mycolic acids Thick waxy hydrophobic cell wall Acid-fast staining for identification Mollicutes (Mycoplasma) No cell wall ~ no peptidoglycan layer Highly pleomorphic and osmotically unstable The smallest bacteria described Bacterial cell structure Alternative structural bacterial envelopes Mycobacteria Mollicutes (Mycoplasma) Bacterial cell structure Capsule: Glycocalyx, an extracellular polymeric matrix Only in some bacterial species Capsule Functions: Protection (environment, phagocytosis) Cell adherence Nutrient reserve Bacterial cell structure Capsule Streptococcus capsule revealed by India Ink Bacterial cell structure Flagella: Anchored to the bacterial cell envelope Multi-protein structure (engine) The number and position vary between bacteria Functions: Locomotion or bacterial motility Flagella Endoflagellum (Spirochetes) Bacterial cell structure Bacterial cell structure Pili/fimbriae: Pili/fimbriae Fine, straight, hair-like appendages attached to cell wall Known as “adhesins” Most common on Gram-negative bacteria Function Adhesion to host tissues (specificity) Contribute to antigenicity Bacterial cell structure Endospores: Cryptobiotic state of dormancy and most durable type of cell found in nature Produced by some Gram-positive bacteria Examples of pathogenic genera: Bacillus and Clostridium Function Ensure survival during adverse environmental conditions Dormant highly resistant bodies Bacterial cell structure