IV.
A.
B.
C.
Bacterial Structure
and Growth
Bacterial Cells: An Overview
Bacterial Cell Structures
Factors that Influence Bacterial Growth
IV. A. Bacterial Cells:
An Overview
• Shapes & Arrangements
– Round Bacteria
Coccus
Staphylococcus
Diplococcus
Tetrad
Streptococcus
Sarcina
– Rod-shaped Bacteria
Bacillus
Streptobacillus
Diplobacillus
Coryneform bacteria
IV. A. Bacterial Cells:
An Overview
• Shapes & Arrangements (cont.)
– Curved & Spiral Bacteria
Vibrio
Spirillum
Spirochaete
IV. A. Bacterial Cells:
An Overview
• Sizes
– Typically ~ 0.1 - 20 m (with some exceptions)
– Typical coccus: ~ 1 m (eg Staphylococcus)
– Typical short rod: ~ 1 x 5 m (eg E. coli)
– Barely within the best resolution of a
good compound light microscope
IV. A. Bacterial Cells:
An Overview
IV. B. Bacterial Cell Structures
1.
Capsules
2.
Cell Wall
3.
Plasma Membrane
4.
Cytoplasm & Cytoplasmic Inclusions
5.
Ribosomes
6.
Bacterial DNA
7.
Pili
8.
Flagella
9.
Spores
IV. B. 1.
Capsules
• Species and strain specific
• Structure
– Polysaccharide or polypeptide layer outside cell
wall
– May be tightly or loosely bound
– Detected by negative staining techniques
IV. B. 1.
Capsules (cont.)
• Functions
– Attachment
– Resistance to desiccation
– Nutrient Storage
– Evasion of phagocytosis
eg. in Streptococcus pneumoniae
S strain is encapsulated & virulent
R strain is nonencapsulated & nonvirulent
IV. B. 2.
Cell Wall
• Gram Staining
– Method developed by Gram in 1888
– Gram-positive cells stain purple
Gram-negative cells stain pink
– Later, it was discovered that the major
factor determining Gram reactions is the
bacterial cell wall structure
– “Gram-positive” & “Gram-negative”
These terms can mean either:
Staining results, or
Types of cell wall structure
IV. B. 2.
•
Cell Wall
Peptidoglycan Structure
– Composition
•
A Polysaccharide
•
Composed of alternating units of
N-acetylglucosamine (NAG) and
N-acetylmuramic acid (NAM)
– Peptide Crosslinking Between
NAM units
– Much thicker and more crosslinking
in Gram-positive than in
Gram-negative Bacteria
IV. B. 2.
Cell Wall
• Gram-positive Cell Wall
– Thick Layer of Highly Crosslinked
Peptidoglycan
– Teichoic Acid Strands
IV. B. 2.
Cell Wall
• Gram-negative Cell Walls
– Outer Membrane
•
Lipopolysaccharide Layer
containing Lipid A
•
Phospholipid Layer
•
Outer Membrane Proteins
– Thin Layer of Peptidoglycan
with no teichoic acid
– Periplasmic Space
IV. B. 2.
Cell Wall
• Variations on Cell Wall Architecture
– Acid-fast Cell Walls
•
Similar to Gram-positive structure, but
have Mycolic Acid: A waxy lipid
•
Require special acid-fast staining technique
•
Includes Mycobacterium and Nocardia
IV. B. 2.
Cell Wall
• Variations on Cell Wall Architecture (cont.)
– Mycoplasmas
•
Bacteria that are naturally have no cell walls
•
Includes Mycoplasma and Ureaplasma
– Archaeobacteria
•
Have unusual archaeobacterial cell walls
with no peptidoglycan
•
Have unusual metabolisms
•
Share a more recent common ancestor with
eukaryotes than with eubacteria (“true bacteria”)
IV. B. 3.
Plasma Membrane
• Structure
– Phospholipid Bilayer with Associated
Proteins
• Functions
– Maintain Cell Integrity
– Regulate Transport
– Specialized Functions in Bacteria
IV. B. 4. Cytoplasm &
Cytoplasmic Inclusions
• Composition:
– Viscous aqueous suspension of proteins,
nucleic acid, dissolved organic compounds,
mineral salts
• Cytoplasmic Inclusions:
– Metachromatic Granules (Phosphate)
– Starch Granules
– Lipid Droplets
– Sulfur Granules
IV. B. 5.
Ribosomes
• Suspended in Cytoplasm
• Sites of Protein Synthesis
IV. B. 6.
Bacterial DNA
• Chromosomal DNA
• Plasmid DNA
–R-Plasmids
–F-Plasmids
IV. B. 7.
Pili
• Hair-like structures on cell surface
• Functions
–Attachment
–Conjugation
IV. B. 8.
Flagella
• Function
– Motility
Almost all motile bacteria are motile by
means of flagella
– Motile vs. nonmotile bacteria
• Structure
– Filament
Composed of the protein flagellin
– Hook & Rotor Assembly
Permits rotational "spinning" movement
IV. B. 8.
Flagella
• Mechanism of Motility
– “Run and Tumble” Movement
controlled by the direction of the flagellar
spin
– Counterclockwise spin = Straight Run
Clockwise spin = Random Tumble
IV. B. 8.
Flagella
• Chemotaxis
– Response to the concentration of chemical
attractants and repellants
– As a bacterium approaches an attractant:
the lengths of the straight runs increase
– As a bacterium approaches a repellant:
the lengths of the straight runs decrease
IV. B. 9.
Spores
• Function
– To permit the organism to survive during
conditions of desiccation, nutrient depletion,
and waste buildup
– Bacterial spores are NOT a reproductive
structure, like plant or fungal spores
• Occurrence
– Produced by very few genera of bacteria
– Major examples
Bacillus
Clostridium
IV. B. 9.
Spores
• Significance in Medicine & Industry
– Spores are resistant to killing
– Cannot be killed by 100°C (boiling)
– Requires heating to 120°C for 15-20 min
(autoclaving or pressure cooking)
IV. B. 9.
Spores
• Sporulation
– The process of spore formation
– Governed by genetic mechanism
– A copy of the bacterial chromosome is
surrounded by a thick, durable spore coat
– This forms an endospore within a vegetative
cell
– When the vegetative cell dies and ruptures,
the free spore is released
IV. B. 9.
Spores
• Spore Germination
– When a spore encounters favorable growth
conditions
– The spore coat ruptures and a new vegetative
cell is formed
IV. C. Factors that Influence
Bacterial Growth
• Growth vs. Survival
– Bacteria may tolerate or survive under more
extreme conditions than their growth conditions
IV. C. Factors that Influence
Bacterial Growth
• Nutrient Requirements
– Energy Source
Most bacteria are chemotrophs; a few are
phototrophs
– Carbon Source
Most bacteria are heterotrophs; a few are
autotrophs
– Nitrogen, Phosphate, Sulfur, Trace Minerals
IV. C. Factors that Influence
Bacterial Growth
• Nutrient Requirements (cont.)
– Special Requirements
examples: amino acids and enzyme cofactors
(vitamins)
Fastidious bacteria: Strains that are difficult or
impossible to culture due to special growth
requirements
IV. C. Factors that Influence
Bacterial Growth
• Temperature
– Psychrophiles
Grow at ~0°C - 20°C
– Mesophiles
Grow at ~20°C - 45°C
– Moderate Thermophiles
Grow at ~45°C - 70°C
– Extreme Thermophiles
Grow at ~70°C - 100°C
IV. C. Factors that Influence
Bacterial Growth
• pH
– Acidophiles
Grow at ~pH 1.0 - pH 6.0
– Neutrophiles
Grow at ~pH 6.0 - pH 8.5
– Alkalophiles
Grow above pH 8.5
IV. C. Factors that Influence
Bacterial Growth
• Oxygen
– Strict aerobes (Obligate aerobes)
Use oxygen for respiration in their metabolism
Require the presence of a normal oxygen
concentration (~20%) for growth
– Strict anaerobes (Obligate anaerobes)
Oxygen is a poison for these microbes
Cannot grow at all in the presence of oxygen
IV. C. Factors that Influence
Bacterial Growth
• Oxygen (cont.)
– Aerotolerate anaerobes
Do not use oxygen, but oxygen is not a poison for
these
Can grow equally well with or without oxygen
– Facultative anaerobes
Use oxygen for respiration, but can also grow
without oxygen
Grow better with oxygen that without oxygen
IV. C. Factors that Influence
Bacterial Growth
• Oxygen (cont.)
– Microaerophiles
Require low concentrations (~5% - 10%) of oxygen
for growth