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?