Prokaryotic Profiles: Bacteria and Archaea
I.
Structure of a Generalized Prokaryotic Cell
A. All bacterial cells have a cell membrane, cytoplasm, ribosomes, a
chromosome
B. Appendages: Cell Extensions
1.Flagella
a. Motility
b. 1/10 size of eukaryotic flagella
c. Helical and grow from tip
d. Role in disease
e. Basic Parts
1) Filament-long, thin, helical structure composed of proteins
2) Hook- curved sheath
3) Basal body – stack of rings firmly anchored in cell wall
f. Rotates 360 degrees – “run”, “tumble”
g. Flagellar arrangements
1) Monotrichous – single flagellum at one end
2) Lophotrichous – small bunches arising from one end of cell
3) Amphitrichous – flagella at both ends of cell
4) Peritrichous – flagella dispersed over surface of cell
h. Chemotaxis
2.Axial filaments – periplasmic, internal flagella, enclosed between cell
wall and cell membrane of spirochetes, motility
3. Appendages for Attachment and Mating
a. Fimbriae
1) Fine hair-like bristles from the cell surface
2) Function in adhesion to other cells and surfaces
3) Role in disease
b. Pilus (sex pilus)
1) Rigid tubular structure made of pilin protein
2) Found only in Gram negative cells
3) Conjugation; transfer of DNA
4) Adhesion
C. Cell Envelope
1.Glycogalyx
a. Coating of molecules external to the cell wall, made of sugars
and/or protein
b. Two types
1) Slime layer – loosely organized and attached
2) Capsule – highly organized and tightly attached
2.Functions
a. Attachment
b. Inhibits killing by white blood cells
c. Bacillus anthracis, Streptococcus pneumoniae
D. Structure of Cell Wall
1.Determines shape, provides support
2.Peptidoglycan
a. Unique macromolecule composed of a repeating framework of
long glycan chains cross-linked by short peptides
b. Provides strong, flexible support to keep bacteria from bursting
or collapsing because of changes in osmotic pressure
c. Drug target
d. 100+ types known
e. not found in archaea or eukaryotes
f. N-acetylglucosamine (NAG); N-acetylmuramic acid (NAM)
g. Adjacent rows linked by polypeptides using D and L forms
3.Four groups based on cell wall composition
a. Gram positive cells
b. Gram negative cells
c. Bacteria without cell walls
d. Bacteria with chemically unique cell walls
4. Gram positive cell wall
a. Consists of
1) Thick, homogenous sheath of peptidoglycan 20-80 nm
2) Tightly bound acidic polysaccharides, including teichoic
acid and lipoteichoic acid; antigenic
3) Cell membrane
b. Retain crystal violet and stain purple
5. Gram negative cell wall – unlike any other in nature
a. Consists of
1) Outer membrane containing lipopolysaccharide (LPS)
2) Thin shell of peptidoglycan
3) Periplasmic space
4) Inner membrane
b. Lose crystal violet and stain re from safranin counterstain
c. Outer membrane acts like partial sieve
6. Practical Considerations of Differences in Cell Wall Structure
a. Outer membrane protects Gb. Exception is alcohol-based compounds
c. Different drugs for G+ and Gd. Role in disease; endotoxins (G-) and proteins on G+
7. Nontypical Cell Walls
a. Mycobacterium and Nocardia
1) Mycolic acid
2) Acid-fast staining
3) Very resistant to certain chemicals
b. Archaea
c. Mycoplasmas
d. L forms of bacteria that have lost cell wall
II.
E. Cell Membrane Structure
1.Very thin lipid layer and proteins
2.No sterols except in mycoplasmas
3. Mesosomes
4. Functions
a. Site for energy reactions, nutrient processing
b. Regulates transport into and out of cell
c. Selectively permeable
d. Most enzymes of respiration in membrane
Bacterial Form and Function: Internal Structures
A. Contents of the Cell Cytoplasm
1.Cytoplasm
a. Dense gelatinous solution of sugars, amino acids and salts
b. 70-80% water
c. Serves as solvent fro materials used in all cell functions
2. Bacterial Chromosomes and plasmids
a. Single, circular double-stranded DNA molecule that contains
all the genetic information required by a cell
c. DNA is tightly coiled around a protein, aggregated in a dense
area called the nucleoid
d. NO NUCLEUS
e. Plasmids
1) Small, circular double-stranded DNA
2) Free or integrated into the chromosome
3) Duplicated and passed on to offspring
4) Not essential to bacterial growth and metabolism
5) May encode antibiotic resistance, tolerance to toxins
6) Used in genetic engineering
3. Ribosomes: Sites of Protein Synthesis
a. rRNA (60%) and protein (40%)
b. 70S; 30S and 50S
4. Inclusions or Granules: Storage Bodies
a. Intracellular storage bodies
b. Vary in size, number and content
c. Bacterial cell can use them when environmental sources are
depleted
d. Examples: glycogen, gas vesicles, sulfur and phosphate
B. Bacterial Endospores
1.Introduction
a. Resting, dormant cells
b. Produced by some G+ genera: Clostridium, Bacillus,
Sporosarcina
c. Have two-phase life cycle- vegetative cell and an endospore
2.Endospore formation and Resistance
a. Sporulation – formation of endospores
b. Stimulus is depletion of nutrients
c. Hardiest of all life forms
d. Withstand extremes in heat, drying, freezing, radiation and
chemicals
e. NOT a means of reproduction
f. Dehydrated and metabolically inactive
g. Longevity verges on immortality
III.
IV.
3. Germination of Endospores
a. Germination – return to vegetative growth
b. Happens in water and germination agent
c. Pressurized steam at 120 degrees for 20-30 minutes will
destroy
Bacterial Shapes, Arrangements, and Sizes
A. Shapes
1.Cocci – spherical
2.Bacilli – rods
3. Spiral
a. Vibrio
b. Spirillum
c. Spirochete
B. Arrangements
1.In cocci
a. Diplococci
b. Tetrads
c. Staphylococci – clusters
d. Streptococci – chains
2.In bacilli
a. Single cell
b. Diplobacilli
c. Streptobacilli
Bacterial Identification and Classification Systems
A. Methods used in Bacterial Identification
1.Microscopic morphology
2.Macroscopic morphology
3. Physiological/biochemical characteristics
4. Chemical analysis
5. Serological analysis
6. Genetic and Molecular analysis
a. G+C base composition
b. DNA analysis using genetic probes
c. Nucleic acid sequencing and rRNA analysis
B. Classification Systems in the Prokaryotae as per Bergey’s Manual
1.Gracilicutes – G- cell walls, thin-skinned
2.Firmicutes – G+ cell walls, thick-skinned
3. Tenericutes – lack a cell wall and are soft
V.
4. Mendosicutes – archaea, primitive prokaryotes with unusual cell walls
and nutritional habits
5. Species – share overall similar traits
6. Strain – from single parent but differs in structure
7. Type – subspecies differing in antigenic makeup
Survey of Prokaryotic Groups with Unusual Characteristics
A. Unusual forms of Medically Significant Bacteria
1.Rickettsias
a. Very tiny, Gb. Alternate between mammals and arthropods
c. Obligate intracellular pathogens
d. Rickettsia rickettsii – Rocky Mt. Spotted fever
e. Rickettsia prowazekii – epidemic typhus
f. Coxiella burnetii – Q fever
2.Chlamydias
a. Tiny, Gb. Obligate intracellular parasites
c. Not transmitted by srthropods
d. Chlamydia trachomatis – eye infection and STD
e. Chlamydia psittaci – ornithosis, parrot fever
f. Chlamydia pneumoniae – lung infections
3. Mycoplasmas
a. Naturally lack a cell wall
b. Stabilized by sterols, resistant to lysis
c. Extremely small
d. Mycoplasma pneumoniae