Prokaryotes: Bacteria & Archaea
Lecture 3 Introduction
• 3 Major Bacterial Shapes
– Cocci, Bacilli, Spiral-shaped
• Prokaryotic Structures
– Flagella and Motility
– Fimbriae and Pili
– Cell Envelope
• Glycocalyx
• Cell Wall
• Cell Membrane
–
–
–
–
Gram Positive vs Gram Negative Cells
Cytoplasm and Bacterial Genome
Ribosomes, Inclusions, Granules
Bacterial Endospores
Three Major Bacterial Shapes
• Cocci – round, spherical
• Bacilli – rod
• Spiral – helical, comma, twisted rod,
spirochete
Cocci
Coccus – single spherical bacteria
• Bacteria can also be categorized
according to arrangement, or
style of grouping.
• The greatest variety of
arrangement occurs in cocci.
• Factors determining arrangement
include pattern of division and
how the cells remain attached
afterward.
Diplococci – pair
Streptococci – long chain
Tetrad – group of four
Sarcinae – cubical packet
Staphylococci – irregular cluster
Bacilli
• Divide only in one plane
• Have varied forms depending
on species: blocky, spindles,
clubbed, drumstick, threadlike
Diplobacilli – pair
Streptobacilli – long chain
Coccobacillus – short and
plump rod
Palisades – cells of a chain
remaining partially attached
by a small hinge region at the
ends
Spiral
Vibrio – curved Rod, comma
Spirillum – 2 or more turns with
a rigid helix; external flagella
Spirochete – 3 or more turns
with a flexible helix; internal
flagella
• Spirilla are occasionally
found in short chains
• Spirochetes rarely remain
attached after division
Pleomorphism: Cells of a single species varying in shapes and sizes
Structure of a Typical Bacterial Cell
Prokaryotic Flagella
• 3 parts
- filament
- hook
- basal body
• Made of flagellin
protein
• Rotates 360º
• Used for motility
• Outside of cell wall
Flagellar Arrangement
Flagellar Motility
• When flagella rotate counterclockwise, the cell swims forward in runs.
• When flagella reverses direction and rotate clockwise, the cell stops and
tumbles
Bacterial Chemotaxis
Chemotaxis: movement in response to a chemical gradient
(toward an attractant or to avoid a repellant)
Axial Filament
• Periplasmic Flagella: internal flagella enclosed in the space between the outer
sheath and the cell wall
• Found only in Spirochetes
• Made of Flagellin protein
Fimbriae
• Short,
fine and numerous fibers
• Promote virulence by being
involved in Adhesion & Attachment
Neisseria gonorrhoeae
Escherichia coli
Pili
• Also called a Sex Pilus
• A rigid, tubular structure
made from Pilin protein
• Found only in Gram (-)
Bacteria
• Involved in Conjugation:
bacterial “mating” process
Cell Envelope
Glycocalyx
• Coating layer outside of the
cell wall
• Made of proteins & many
carbohydrates (very sticky)
• 2 types of Glycocalyx
- Slime layer (loose)
- Capsule (structured)
• Involved in Attachment,
Resisting Osmolarity changes,
Phagocyte avoidance
What a difference a Glycocalyx makes!
Streptococcus pneumoniae
Klebsiella pneumonia
Biofilms
A complex association that arises from
microorganisms growing together and
interacting on the surface of a habitat
Occur naturally in the environment but
in humans can pose a threat when
accumulate on catheters, heart valves,
hip joints, and teeth.
Cell Wall
• Determines shape of bacteria
• Prevents osmotic lysis
• Generally composed of
Peptidoglycan (in bacteria)
Peptidoglycan
A network of polysaccharide chains
cross-linked by short peptides that
forms the rigid part of bacterial cell
walls.
• Polymer of 2 glycans
- N-acetylglucosamine (NAG)
- N-acetylmuramic acid (NAM)
• Linked by polypeptides
Gram Positive Cell Wall
Consists of:
• Thick peptidoglycan
layer (20-80 nm)
• Teichoic and
lipoteichoic acids
• Narrow Periplasmic
Space
• Cell membrane
Gram Negative Cell Wall
Consists of:
• An outer membrane
that contains
lipopolysaccharide
(LPS)
• Thin peptidoglycan
layer (8-11 nm)
• Extensive Periplasmic
Space
• Inner cell membrane
Gram (+) vs. Gram (-)
The Gram Stain
Plasma Membrane
• Phospholipid bilayer with proteins and carbohydrates
• Selectively permeable
• No sterols in Prokaryotes (except Mycoplasma)
• Involved in Transport of molecules
• Involved in Metabolic Activity
Atypical Cell Walls and/or Membranes
• Bacteria without cell walls - Mycoplasma
– Have only a cell membrane containing sterols for
strength
• Bacteria with some peptidoglycan and a lot of
mycolic acid - Mycobacterium
• Archaea have protein cell walls, polysaccharide
cell walls or no cell wall at all.
– No Peptidoglycan
Cytoplasm
• Dense gelatinous
solution of sugars,
amino acids, & salts
(70-80% water)
• Nucleoid: a central area in
the cell where the bacterial
chromosome aggregates
• Ribosomes
• Inclusions & Granules
Bacterial Genome
1. Bacterial Chromosome
2. Plasmids
•
Single (One Copy)
•
Small
•
Circular DNA
•
Circular DNA
•
Double Helix
•
•
Codes for all essential
genes
Genes not essential
for cell growth but
can code for genes
for adaptive traits
• Can be transmissible
to other bacteria
• Can contain genes
that provide antibiotic
resistance.
Ribosomes
• Made of ribosomal
RNA & protein
• Prokaryotic differ
from eukaryotic
ribosomes in size
• Site of protein
synthesis
• All cells have
ribosomes
Inclusions & Granules
• Inclusions: intracellular storage of
metabolic products
• Vary in size, number & content
• Granules: contain crystals or
inorganic compounds
Magnetotactic Bacteria
Purple Sulfur Bacteria
Bacterial Endospores
• Resting, dormant cells
• Only produced by three G+ genera: Clostridium, Bacillus &
Sporosarcina
• Have a 2-phase life cycle – vegetative cell & an endospore
- sporulation
- germination
Endospores
• Dehydrated,
metabolically inactive
• Spore coat
• Extraordinarily resistant
and long lasting