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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: ?
Bacterial Cell Structure
Fig 3.1
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
Compare to Figs. 3.4 and 3.5
palisades
Figure 4.4
Spiral Bacteria
External Structures Appendages located outside of cell envelope
Structure Function
Flagellum /-a
Axial filaments
Fimbria /-ae
Pilus /-i
Monotrichous Peritrichous Amphitrichous Lophotrichous Atrichous
?
Motility • Due to rotation of flagella
• 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
• 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)
Cell Envelope: Wall and Membranes
Fig 4.12
Gram + Cell Wall • Peptidoglycan layer
thick
• Negatively charged (lipo)teichoic acid on surface
• Peptidoglycan layer thin
• Outer membrane
• Periplasmic space
Gram – Cell Wall
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
No outer membrane
Generally easier to kill. Many antibacterial compounds target Peptidoglycan layer (E.g.:_______________, _______________)
Gram negative
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.
For details and practical application of Gram staining see lab!
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)
Nontypical Cell Walls
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
• 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)
Contents of Cytoplasm
Plasmids: small, nonessential, circular DMA (5 – 100 genes)
Replicate independently
Endospores
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
For special staining technique: see lab!
Fig. 3.21
Sporulation & Germination
The Medical Significance of Bacterial ESs
Disease Bacillus anthracis
Clostridium botulinum
Clostridium difficile
Clostridium perfringens
Clostridium tetani
• 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
Based on phenotypic characteristics, i.e.: morphology, differential staining, and biochemical tests
Bergey’s Manual of Systematic Bacteriology Provides phylogenetic information
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?