Ch 3 Bacteria and Archaea
SLOs for Culturing of Microorganisms Compare and contrast the overall cell structure of prokaryotes and eukaryotes. List structures all bacteria possess. Describe three basic shapes of bacteria. Provide terms to describe bacterial arrangements. Describe structure and function of S-layer, glycocalyx, slime layer, flagella, fimbriae, and pili. Explain how a flagellum works in the presence of an attractant. Discuss the structural and functional dfference between the two main types of bacterial envelopes. Name a substance in the envelope structure of some bacteria that can cause severe symptoms in humans. Describe bacterial chromosomes, plasmids, and ribosomes. Detail the causes and mechanisms of sporogenesis and germination. Differentiate between Bergey s Manual of Systematic Bacteriology and Bergey s Manual of Determinative Bacteriology.. Define species and subspecies in terms of bacteria.
Form and Function of Bacteria and Archaea Bacteria and Archaea are ubiquitous
Comparing Prokaryotic and Eukaryotic Cells Common features? Distinctive features:?
Fig 3.1 Bacterial Cell Structure
Bacterial Shapes, Sizes, and Arrangement Average size: 1 µm 2-8 µm Mycoplasma: 0.15 -.3 µm Three basic shapes 1. Bacillus, -i 2. Coccus, -i 3. Spirals (Vibrio, Spirillum, Spirochete) Most monomorphic, some pleomorphic Variations in cell arrangements (esp. for cocci)
Pleomorphic Corynebacteria Monomorphic E. coli
Cell Arrangement palisades Compare to Figs. 3.4 and 3.5
Spiral Bacteria Figure 4.4
External Structures Appendages located outside of cell envelope Structure Function Flagellum /-a Axial filaments Fimbria /-ae Pilus /-i? Monotrichous Peritrichous Amphitrichous Lophotrichous Atrichous
Due to rotation of flagella Motility Mechanism of rotation: Run and tumble Move toward or away from stimuli (taxis) Positive and negative Chemotaxis Figs 3.8 and 3.9
Fimbriae and Pili Fimbriae adhere help with attachment Pili made of pilin protein: transfer DNA from one cell to another conjugation?? Fig 3.11
Surface Coatings as part of Cell Envelope S layer (surface layer) consists of monomolecular protein layer. Function? Glycocalyx: Many bacteria secrete external surface layer composed of sticky polysaccharides, and/or glycoproteins Capsule: organized and firmly attached to cell wall Slime layer: unorganized and loosely attached Allows cells to attach key to biofilms Prevents phagocytosis virulence factor E.g.: B. anthracis, S. pneumoniae
Cell Envelope: Wall and Membranes Rigid for shape & protection prevents osmotic lysis Consists of Peptidoglycan (PG) polymer of 2 monosaccharide subunits N-acetylglucosamine (G or NAG) and N-acetylmuramic acid (M or NAM) Linked by peptides (peptide cross-links) Fully permeable to ions, aa, and sugars (Gram + cell wall may regulate movement of cations) Fig 4.12
Gram + Cell Wall Peptidoglycan layer thick Negatively charged (lipo)teichoic acid on surface Gram Cell Wall Peptidoglycan layer thin Outer membrane Periplasmic space
Gram-negative Cell Wall Lipid A of LPS acts as endotoxin; O polysaccharides are antigens for typing, e.g., E. coli O157:H7 Gram neg. bacteria are less sensitive to medications because outer membrane acts as additional barrier. LPS layer = outer layer of outer membrane (protein rich gel-like fluid)
Review of Differences in Cell Envelope Structure Gram positive Gram negative No outer membrane Generally easier to kill. Many antibacterial compounds target Peptidoglycan layer (E.g.:, ) For details and practical application of Gram staining see lab! Outer membrane of gram-negative bacteria serves as extra barrier. Impervious to certain antimicrobial chemicals. More difficult to kill or inhibit than gram-positive bacteria. Alcohol-based compounds work well as disinfecctants and antiseptics Special antibiotics needed that can cross the outer membrane.
Nontypical Cell Walls Acid-fast Cell Walls Genus Mycobacterium and Nocardia (read medical moment) Mycolic acid (waxy lipid) covers thin peptidoglycan layer Do not stain well with Gram stain use acid-fast stain (see lab)
No Cell Wall: Mycoplasmas Mycoplasma have cell membrane which incorporates cholesterol compounds (sterols), similar to eukaryotic cells Cannot be detected by typical light microscopy M. pneumoniae causes EM of M. hyorhinis Shape?
Cytoplasmic Membrane Structure Analogous to eukaryotic cell membrane: Phospholipid bilayer with proteins (Fluid mosaic model) Permeability barrier: Selectively permeable Diffusion, osmosis and transport systems: Regulation of nutrients and waste transport Different from eukaryotic cell membrane: Role in Energy transformation/production???
Fig 4.14
Bacterial Internal Structures Contents of Cytoplasm 70 80% water Complex mixture of sugars, amino acids, and salts Contains building blocks for cell synthesis or sources of energy Location of most biochemical activities Nucleoid: Region containing bacterial chromosome. Difference between human and bacterial chromosomes? Ribosomes (smaller than in eukaryotes) Function? Inclusion bodies: granules containing nutrients, monomers, Fe compounds (magnetosomes)
Plasmids: small, nonessential, circular DMA (5 100 genes) Replicate independently
Endospores For special staining technique: see lab! Dormant, tough, non-reproductive structures; germination vegetative cells Spore forming genera: Resistance to UV and radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants Relationship to disease Sporulation: Endospore formation Germination: Return to vegetative state
Sporulation & Germination Fig. 3.21
The Medical Significance of Bacterial ESs Bacillus anthracis Clostridium botulinum Clostridium difficile Clostridium perfringens Clostridium tetani Disease Ubiquitous in soil and dust Boiling will not kill ESs use pressurized steam chambers: Pressure cooker, autoclave
Archaea the other Prokaryotes Extremophiles: Some live at extreme temperatures Some are halophiles or acidophiles Some live on sulfur or methane. No known human pathogens yet. However, now some found on/in human body. May be capable of causing human disease?
Classification Systems for Bacteria and Archaea Two comprehensive Databases: Bergey s Manual of Determinative Bacteriology Provides identification schemes for identification of based on traits commonly assayed in clinical, teaching, and research labs Bergey s Manual of Systematic Bacteriology Provides phylogenetic information Based on phenotypic characteristics, i.e.: morphology, differential staining, and biochemical tests Based on rrna sequencing
Species and Subspecies in Bacteria Bacterial species Used to be collection of bacterial cells, sharing an overall similar pattern of traits. Should share at least 70% - 80% of their genes. Now some rearrangement due to (?) Subspecies, strains, or types Bacteria of the same species that have differing characteristics. E.g.: E.coli K-12 and E.coli O157:H7 Serotype Subset of a species that stimulates a distinct pattern of antibody (serum) responses.
Case File: C. diff Inside the Clinic: A Sticky Situation Who will present?