bacterial morphology, metabolism and growth
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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 pallidum-
Syphilis_Frengi)– Fluorescence– Phase contrast (details of the living cell)
• Electron
Staining
• Simple• Differential: Gram and Acid-fast stain
Gram-stain: cell wallAcid 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 Prokaryote• Size >5 μm 0,5-3 μm• 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
EucaryoteProkaryote
• CytoplasmicStructuresMitokondria + -Golgi bodies + -Endoplasmic reticulum + -Ribosomes 80S(60S+40S) 70S(50S+30S)Cytoplasmic membrane with sterols no sterol
Major characteristics of Eucaryotic and prokaryotic cell
Eucaryote Prokaryote
• Cell wall -/composed of kitin complex structure(protein, lipits and peptidoglycans)
• Reproduction sexual and asexual asexual (binaryfission)
• Movement complex flagellum simple flagellum(If present) (If present)
• Respiration via mitokondria 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
Diplococcus
Clusters: staphylococcus
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 gram-negative 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 gram-negative)
• 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 proteins-lectins that bind to spesific sugars-mannose
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-carboxypeptidases-
penicillin-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 beta-lactam 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
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