Bacterial morphology,
metabolism and growth
Dr Ömer Küçükbasmacı
Cell
• Fundemental unit of living things
(smallest bacterium-largest plants-animals)
Bacteria
• The smallest cells
• Visible only with the aid of a microscope
• The smallest bacteria: Chlamydia and
Rickettsia-0.1-0.2 micrometer
• Larger bacteria: many microns in length
A newly described species
• Hundred of times larger than the average
bacterial cell
• Is visible to the naked eye
Diversity!
Most bacterial cells
• Approximately 1 micrometer in diameter
• Visible by light microscope
• Resolution: 0.2 micrometer
Microscopes
• Light:
– Bright-field
– Dark-field (Treponema pallidumSyphilis_Frengi)
– Fluorescence
– Phase contrast (details of the living cell)
• Electron
Staining
• Simple
• Differential: Gram and Acid-fast stain
Gram-stain: cell wall
Acid fast stain: Mycobacterium
• Negative stain: Indian ink
(capsule)
• Special staining
Animal and plant cells
• Much larger
• Ranging from 7micrometer (red blood
cells)
• To several feet (certain nerve cell)
Each cell
• Genetic basis for reproduction (DNA
genome)
• Biochemical machinery (genetic
information is transcribed in mRNA and
mRNA translated in proteins)
• The machinery for energy production and
biosynthesis
• This is all packaged by a membrane.
Each cell
• Replicates by cell division.
Cells
• Eukaryotic (Greek for true nucleus)
• Prokaryotic (Greek for primitive nucleus)
Eucaryotes
• Animals
• Plants
• Fungi
Procaryotes
• Bacteria
• Blue-green algae
Major characteristics of Eucaryotic
and prokaryotic cell
Eucaryote
>5 μm
Prokaryote
0,5-3 μm
• Size
• Nuclear
structure :
Nucleus
classic membrane no membrane
Chromosomes
strands of DNA
single circular DNA
diploid genome
haploid genome
Major characteristics of Eucaryotic
and prokaryotic cell
Eucaryote
• Cytoplasmic
Structures
Mitokondria
+
Golgi bodies
+
Endoplasmic
reticulum
+
Ribosomes 80S(60S+40S)
Cytoplasmic
membrane with sterols
Prokaryote
70S(50S+30S)
no sterol
Major characteristics of Eucaryotic
and prokaryotic cell
Eucaryote
• Cell wall
-/composed of kitin
Prokaryote
complex structure
(protein, lipits and
peptidoglycans)
• Reproduction sexual and asexual
asexual (binary
fission)
• Movement
complex flagellum
(If present)
• Respiration via mitokondria
simple flagellum
(If present)
via cytoplasmic
membrane
Bacteria
• Lack nucleus membrane and membrane bound
organelles
• A smaller ribosome
• Peptidoglycan cell wall which protects it from
environtment with low osmotic pressure, at
temperature extremes (both hot and cold),
dryness and with very dilute and diverse energy
sources.
• They have evolved their structures and functions
to adopt these conditions.
Differences
• Between Eukaryotes and prokaryotes
Differences between Prokaryotes
• Bacteria differ:
-morphology (size, shape, stainig
characteristics)
-metabolic
-antigenic and
-genetic characteristics
Size
• They are diffucult to differentiate by size
Shape
• Spherical: coccus (Staphyloccus)
• Rod-shaped: bacillus (Escherichia)
• Snakelike: spirillum (Treponema)
• Branched filamentous (Nocardia and
Actinomyces)
( Clusters: diplococcus (Neisseria)
chains (Streptococcus)
grapelike (Staphylococcus) )
Bacterial shape
Sperical
(coccus)
Rod-shaped
Spiral
Spiral or spirillum
Helix or spirochete
Bacterial arrangement
Chains: streptococcus
Clusters:
staphylococcus
Diplococcus
Packets of
eight:sarcina
Treponema by dark-field
microscopy
Gram stain
• Two major classes of bacteria are
distinguished:
• Gram-positive and
• Gram-negative bacteria
• Except:
• Mycobacteria (waxy outer shell ,
distinguished by acid fast stain)
• Mycoplasmas(no peptidoglycan)
Bacterial Ultrastructure
• Internal structure
• External structure
• Gram-positive and gram-negative bacteria
have
-Similar internal structure
-But different external structure
Cytoplasm
•
•
•
•
•
DNA chromosome
mRNA
Ribosomes
Proteins
Metabolites
Bacterial chromosome
•
•
•
•
•
Unlike eukaryotes
A single
Double stranded circle
Not in a membrane bound nucleus
In a discrete area called nucleoid
Bacterial chromosome
• Unlike eukaryotes
• No histons
Plasmids
•
•
•
•
•
Smaller
Circular
Extrachromosomal DNAs
Not usually essential for cellular survival
Most commonly found in gram-negative
bacteria
• Often provide a selective advantage:
resistance to antibiotics
Lack of a nuclear membrane
• Simplifies the requirements and
• Control mechanisms for the synthesis of
proteins
Ribosomes
• Unlike the eukaryotic
80S(40S+60S)ribosome
• Bacterial 70S chromosome (30+50S)
• Proteins and RNA of the ribosome are
significantly different
• Major targets for antibacterial drugs
Cytoplasmic membrane
• Lipid bilayer
• Similar to eukaryotic membranes
• But no sterols (cholesterol)
Exception: Mycoplasmas
Cytoplasmic membrane
• Responsible for many functions
• Attributable to organelles in eukaryotes:
-electron transport
-energy production (mitokondria in
eukaryotes)
Cytoplasmic membrane
• Transport proteins: uptake of metabolites
release of other substances
• Ion pumps: to maintain a membrane
potential
• Enzymes
Mesosome
• A coiled cytoplasmic membrane
• An anchor to bind and pull apart daughter
chromosomes during cell division.
Cell wall
• Distinguishes gram-positive and gramnegative bacteria
The cytoplasmic membrane in
most prokaryotes surrounded by
• Rigid peptidoglycan (murein) layer
• Except: Archaebacteria (pseudoglycan
and pseudomurein) and mycoplasmas (no
cell wall)
• Peptidoglycan provides rigidity and
determines the shape of a bacteria
• Gram-negative bacteria. + outer
membranes
Gram positive bacteria
• Thick multilayered cell wall
• Consisting mainly of peptidoglycan
Gram positive bacteria
• Peptidoglycan
• Sufficiently porous(allows diffusion of
metabolites to the plasma membrane)
• Essential for structure, replication, for
survival
Peptidoglycan
•
•
•
•
During infection
İnterferes with phagocytosis
Stimulates lymphoctes
Pyrogenic activity (induces fever)
Peptidoglycan
• Degraded by lysozyme
• Enzyme in human tears, mucus (produced
by bacteria and other organisms)
• Degrades the glycan backbone of the
peptidoglycan which protects it from
osmotic pressure changes
Protoplast
• Removal of cell wall with lysozyme
• Lysis unless it is osmotically stabilized
Gram-positive cell wall
•
•
•
•
Peptidoglycan +
Teicoic acid
Lipoteichoic acid
Complex polisaccarides (C
polysaccharides)
• M protein of streptococci
• R protein of staphylococci
Gram-positive bacteria
• Teicoic acid : covalently linked to peptidoglycan
• Lipoteichoic acid : anchored in the cytoplasmic
membrane
• Common surface antigens
• Distinguish bacterial serotypes
• Promote attachment to other bacteria and to
spesific receptors on mammalian cell surfaces
(adherence)
Gram positive-bacteria
• Teicoic acid: important virulance factors
• Lipoteicoic acid are shed into media and
host
• Although weaker
• Can initiate endotoxic-like activities.
Gram-negative bacteria
• Cell wall is more complex
• Both structurally and chemically
Gram-negative bacteria
• Two layers external to the cytoplasmic
membrane:
• -Thin peptidoglycan layer
• -Outer mebrane (unique to gram-negative
bacteria)
• No teicoic acid and lipoteicoic acid
• +periplasmic space
Periplasmic space
• The area between the external surface of
rhe cytoplasmic membrane and the
internal surface of the outher membrane
Periplasmic space
• A variety of hydrolytic enzymes
• Breakdown of large macromolecules for
metabolism
• Lytic virulence factors ( collagenases,
hyalurodidases, proteases, beta-lactamases)
• Components of sugar transport system
• Binding proteins for the uptake of different
metabolites and of a chemotaxis system
Outer membranes
• Unique to gram-negative-bacteria
• Maintains the bacterial structure
• Permeability barrier to large molecules
and hydrophobic molecules
• Provides protection from adverse
environmental conditions (For
Enterobactericeae from digestive system
of the host)
Outer membranes
• Asymetric bilayer
• The inner leaflet: phospholipits normally
found in bacterial membranes
• Outer leaflet: amphipathic molecule(
having both hydrophobic and hydrophilic
ends) contains Lipopolysaccaride (LPS)
Outer membranes
• LPS molecules are only found in the outer
leaflet
Lipopolysaccaride
• Endotoxin (Lipid A+polysaccharide-O
antigen, antigenic variety is great)
• Powerful stimulator of immune responses
• Causes fever and shock Shwartzman
reaction (disseminated intravascular
coagulation) follows the release of large
amounts of endotoxin.
Outer membrane proteins
• Porins: transmembrane proteins they form
pores allow diffusion of hydrophilic
molecules
• Structural proteins and receptor molecules
for bacteriophages
Disruption of the outher
membrane
• Weakens the bacteria
• +lysozyme
• Spheroplasts (osmotically sensitive) are
formed.
External structures
•
•
•
•
Capsule
Pili
Flagellum
Proteins
Capsules
• Some bacteria (gram-positive and gramnegative)
• Loose polysaccaride or proteinlayer
• Slime layer: loosely adherent and
nonuniform in density and thickness
• Glycocalyx: capsule and slime layer are
also called.
Capsule
• Polypeptide capsule:
• Bacillus anthracis (polyglutamic acid)
Capsule
• Hard to be seen by microscopy
• Negative staining: Indian ink
Capsule
• Unnecessary for growth
• Very important for survival
Capsule
• Poorly antigenic
• Antiphagocytic and a major virulence
factor (Streptococcus pneumoniae)
• Barrier to toxic hydrophobic molecules
such as detergents
• Promote adherence (Streptococcus
mutants: stick the tooth)
Quellung reaction
• For vizualizing the capsule
• Using antibodies
• The capsule is swollen
Flagella (Kirpik)
•
•
•
•
Motility
Protein (flagellin)
Antigenic and strain determinants
Anchored in membranes through a hook
and basal body
• One or several
Flagella
•
•
•
•
Monotrichous
Polar: Pseudomonas aeruginosa
Peritrichous :Escherichia coli
Lophotrichous
Fimbriae (Pili)
• Protein(pilin)
• Different from flagella: smaller in diameter
and not coiled in structure.
• Promote adherence to other bacteria or to
th host (adhesins, lectins, evasins,
aggresins)
Fimbriae (Pili)
• Fimbriae are important virulance factors as
an adhesin in E. Coli (urinary tract),
Neisseria gonorrhoeae
• The tips of fimbriae may contain proteinslectins that bind to spesific sugarsmannose
Fimbriae (Pili)
• F pili (Sex)
• Promote transfer of large segments of
bacterial chromosome between bacteria
• Encoded by a F plasmid.
Bacterial exceptions
•
•
•
•
Mycobacteria
Corynebacterium
Nocardia
Mycoplasmas
Mycobacteria
•
•
•
•
•
•
•
Peptidoglycan (slightly different)
Waxlikelipit coat of mycolic acid
Cord factor
Wax D
Sulfolipids
Acid-fast staining
The coat responsible for virulence and
antiphagocytic.
• Corynebacterium
• Nocardia
Produce mycolic acid lipids.
Mycoplasmas
• No peptidoglycan cell wall
Structure of Bacterial Cell Wall
• The components are large structures
• They are made up of polymers of subunits
• Synthesis of it occurs outside the bacteria
Peptidoglycan
(Mucopeptide, Murein)
• Linear polysaccaride chain:
-repeating disaccarides:
N-acetylglucosamine
N-acetylmuramic acid
• Cross-linked by peptides
Cell wall synthesis
• Cross-linking reaction is catalyzed by:
-membrane bound transpeptidases
-DD-carboxypeptidasespenicillin-binding proteins (PBPs)
Cell wall synthesis
• Penicillin-binding proteins (PBPs):
-remove extra terminal D-alanines
-These terminal D-alanines limit the extent
of cross-linking
-They are targets for penicillin and betalactam antibiotics
Cell wall
• Peptidoglycan is constantly being
synthesized and degraded.
• Autolysins such as lysozyme are important
for determining the shape of bacteria.
Cell wall
• During starvation:
-New peptidoglycan synthesis does not
occur
-Peptidoglycan is weakened
-Gram-staining property changes
(old cultures)
Biosynthesis of peptidoglycan
• Unique to bacterial cells
• İnhibited with no adverse effect of human
cells
• An important target for antibiotics
(selective toxicity)
Lipopolysaccaride
• Lipid A
• Core polysaccaride
• O antigen
Lipoppolysaccaride
• Lipid A:
basic component
essential for bacterial viability
endotoxin activity
• O antigen: antigenic part (serotypes)
Inclusion granules
•
•
•
•
Storage of energy
Poly-beta-hydroxybutyric acid (PHB)
Glycogen
Polyphosphate
Inclusion granules
• Polymetaphosphate: Corynebacterium
-Babes-Ernst bodies
Spores
• Resistant to harsh conditions
• (loss of nutritional requirement,
dessication, intense heat, radiation and
attack by most enzymes and chemical
agents)
Spores
• Exist for centuries
• Diffucult to decontaminate with standart
disinfectants
Spores formers:
• Some gram-positive
• Never gram-negative
Spore formers
• Bacillus
• Clostridium
Kinds of spores
• Endospore: Bacillus subtilis
• Terminal endospore: Clostridium tetani
‘drumstick’
• Subterminal: Clostridium botulinum
Under harsh conditions
• Vegetative state is converted to dormant
state (spore)
Localisation of the spore within
a cell
• Characteristic of bacteria
• Can assist in identification of the
bacterium.
Spore
• Dehydrated
• Multishelled structure
• A complete copy of chromosome
• Minimum concentration of proteins and
Ribosomes + High concentration of calcium
bound dipicolinic acid
Spore
• Outside the core:
-inner membrane
-spore wall
-cortex
-outher membrane
-keratin-like protein coat
-exosporium
Sporulation
• 6-8 hours
Germination
• Spor__vegetative state:
disruption of the outher coat
by mechanical stress, pH, heat or
another stressor
It takes about 90 minutes
Bacterial metabolism
• Bacterial growth:
-a source of energy
-raw materials
*To build the proteins, structures and
membranes
*That make up the structure and
biochemical machines of the cell
Bacterial metabolism
• Bacteria should obtain or synthesize:
-aminoacids
-carbohydrates
-lipids as building blocks of the cell
The minimum requirement for
growth
•
•
•
•
•
Carbon
Nitrogen
Energy source
Water
Various ions
• Chemotrophs:
derive energy from inorganic material
• Chemoorganotrophs:
Most bacterial
Heat
• Cardinal temperatures:
-minimum temperature
-optimum temperature
-maximum temperature
Temperature
•
•
•
•
Psychrophiles
Mesophiles
Thermophiles
Hyperthermophiles
ph
• Acidophiles: Below pH 5 (many fungi)
• Alkaliphiles: Above pH 9 (Vibrio)
• Neutral pH: most pathogens
Oxygen requirement
• Obligate anaerobes :
Clostridium perfringens
• Obligate aerobes
• Facultative anaerobes
• Microaerophilic
Incubation for growth
• Aerobic
• Anaerobic
• Capneic (%5 Carbon dioxide)
Methabolism
• Catabolism: substrate breakdown and
conversation into usable energy
• Anabolism: synthesis of cellular
constituents (cell wall, proteins,fatty acids,
nucleic acids
Bacterial growth
• Bacterial replication
• Two equivalent daughter cells
• Binary fission
(Escherichia coli: 20 minutes
Mycobacterium much slower: 12-24h)
Bacterial growth curve
•
•
•
•
Lag phase
Exponential phase
Stationary phase
Death phase