Bacteria structure lecture note 12

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Study of Bacteria and Bacterial cell : 

Study of Bacteria and Bacterial cell Prepared by Dr.R.M.Patel, Departement of Pharmaceutics S.K.Patel College of Pharma. Edu. & Res., Ganpat University

Contents : 

Contents Morphology Size Shape Arrangement Structure of Bacteria Structures External to the cell wall Glycocalyx S-Layers Flagella Fimbrae and Pili Cell wall Structure Gram +ve Cell wall Gream –ve cell wall Structures Internal to the cell wall Cell (Cytoplasmic) Membrane Protoplasm Nucleoid Ribosomes Inclusions Endospores

Morphology of Bacteria : 

Morphology of Bacteria Size Average bacteria 0.5 - 2.0 µm in diameter. Nanobacteria: approx 0.2 µm diameter, most are uncultured Giant bacteria: Epulopiscium fisheloni: 80 µm x 600 µm long, surgeonfish intestines Thiomargarita namibiensis: 100 to 750µm diameter(300µm), ocean sediments Surface Area ~12 um^2 Surface Area to Volume is 3:1 Importance of being small size large surface area-to-volume ratio which allows for rapid uptake and intracellular distribution of nutrients and excretion of wastes. No circulatory mechanism for distribution of nutrients because nutrients are very close to the surface.

Size of bacteria : 

Size of bacteria

Morphology of Bacteria : 

Morphology of Bacteria Shape s Bacillus (rod), Coccus (sphere), spirillum (helical), spirochete (helical, special flexible wall), vibrio (curved rod, comma), coccobacillus (very short rods with rounded ends)

Morphology of Bacteria: Shapes : 

Morphology of Bacteria: Shapes Pleomorphic- having many variations in shape. Eg.Arthrobacter. Prosthecates- external appendages-stalks

Arrangement (Grouping of cells) : 

Arrangement (Grouping of cells) The arrangement of cells is typical of various species or groups of bacteria. Arrangement is depend on the plane of division and separation of dividing cells. Diplo- (i.e. diplococcus), pairs Strepto-chains Staphylo- clusters Tetrads- squares of 4 cells Sarcinae- cubical packets of 8 cells. Eg. Micrococcus Trichomes-eg. Beggiatoa and Saprospira Others Palisade arrangement:Corynebacterium diphtheriae

Arrangements (Grouping of cells) of Cocci : 

Arrangements (Grouping of cells) of Cocci Diplococcus pneumoniae Streptococcus lactis Gaffyka tetragena Staphylococcus aureus Micrococcus

Arrangements of Bacilli : 

Arrangements of Bacilli Bacillus subtilis Klebisella pneumoniae

Spiral and other arrangements : 

Spiral and other arrangements Spirillum ruprem Haloarcula

Prokaryotic structure : 

Prokaryotic structure

structure of Bacteria : 

structure of Bacteria Structure Structures External to the cell wall Glycocalyx S-Layers Flagella Fimbrae and Pili Cell wall Structure Gram Positive cell wall Gram Negative cell wall Structures Internal to the cell wall Cell (Cytoplasmic) Membrane Protoplasm Nucleoid Ribosomes Inclusions Endospores

Structure external to the cell wall : 

Structure external to the cell wall Glycocalyx(Glyco-Sugar coat) Polysaccharide layer external to cell wall polysaccharides including dextran and glucans Some are composed solely of amino acids Not produced by all bacteria Synthesis is usually regulated Storage and/or protection If organized and firmly attached to the cell wall, glycocalyx is referred as capsule. If unorganized and loosely attached to the cell wall, glycocalyx is referred as slime layer.

Glycocalyx : 

Glycocalyx 1. Slime layers Loose & soluble Made up of polysaccharides Protects against drying Biofilm formation

External structures : 

External structures 2. Capsule Viscous substance forming covering layer around the cell wall Thick and tightly bound Made up of Polysaccharides(S.muatans and klebsiella pneumoniae) and polypeptides (B.anthracis) Functions Antiphagocytic and protects against drying Block the attachment of bacteriophages. Attachment to surfaces and forming biofilms (i.e. teeth in dental plaques) eg. Streptococcus mutans.

External structures:Glycocalyx : 

External structures:Glycocalyx 3. Sheath Found mostly in aquatic bacteria, but not all Highly organized external layer Form long chains in flowing, aqueous habitat Protects against disruption by current and dispersal from preferred habitat

Slide 18: 

External structures: Glycocalyx

S-Layers : 

S-Layers Found on some Gram+ and Gram- bacteria and common among Archaea In Gram – bacteria, adheres directly to the outer membrane In Gram + bacteria, associated with the peptidoglycan Regularly structured layer of protein or glycoprotein Pattern like floor tiles Protects against: ion and pH fluctuation Osmotic stress Hydrolytic enzymes Predators such as Bdellovibrio Also helps to confer cell shape to an extent and provide structural support Promote cell adhesion to surfaces. Protect against complement attack and phagocytosis.

Flagella : 

Flagella Hair like, helical appendages protruding through the cell wall. Confer swimming motility in liquids 20 nm diameter x 15-20 um length Not found on all bacteria Complex protein structure

Flagella: Arrangements : 

Flagella: Arrangements Varies depending on the bacterial species. Foure types based on location of flagella Monotrichous: flagella located at one end of the bacterium eg. Pseudomonas aeruginosa, Vibrio cholera Amphitrichous: flagella either single or clusters at both cell poles. Eg. Aquaspirillum serpens, Alcaligenes fecales Lophotrichous: cluster of flagella at one or both ends. Eg. Pseudomonas fluorescens, Rhodospirillum photometricum Peritrichous:spread over the whole structure of Bacteria. Eg.Salmonella typhi, Escherichia coli Proteus vulgaris

Flagella Location : 

Flagella Location Monotrichous Amphitrichous Lophotrichous Peritrichous

Flagella Structure : 

Flagella Structure Flagella structure can be Visualized under microscope into three parts namely: Filament Hollow, rigid, helical cylinder Composed of flagellin proteins(MW 30,000 to 60,000) Growth occurs at distal end Subunits move down hollow core Assemble spontaneously (self-assembly) Hook Anchored to cell wall Basal Body Motor for rotation Spins like a propeller

Slide 24: 

Structure of the flagellum

Flagella and Taxis : 

Flagella and Taxis Taxis- movement toward or away from a stimulus Attractants vs. Repellants Chemotaxis Phototaxis Aerotaxis Magnetotaxis Not a constant path- runs and tumbles due to rotational direction of flagellum winding and unwinding

Flagella and Motility : 

Flagella and Motility

Pili (Fimbriae) : 

Pili (Fimbriae) Short hairlike external appendages Functions: Attachment devices · Produce chemical called adhesin · Binds to specific molecules · E. coli enterotoxic strains bind to small intestine walls using adhesions and fimbriae Movement of populations of bacteria on solid media · Gliding and twitching · Requires cell to cell contact Involved in conjugation · Sex pili or F pili · Allows direct transfer of DNA from one bacterial cell to another · Tend to be longer than other pili

Slide 28: 

Pili (Fimbriae)

Cell wall Structure : 

Cell wall Structure Present in most bacteria- exception is Mycoplasma sp. (M. pneumoniae) which has only a cell membrane- they produce sterols in their membranes which help give them some rigidity. Required to withstand osmotic pressure from within and prevent cell from bursting and confers cell shape Approx. 75 psi- constantly in aqueous environment with low [solute] Part of cell wall serves as antigenic marker = immune system recognizes as invader Often the target of antimicrobial drugs- if a cell cannot synthesize a new cell wall as it multiplies, it cannot grow About 100 different types known but two major groups: Gram+ & Gram- Share in common peptidoglycan but usually thin layer in Gram– and thick layer in Gram+

Cell wall Structure : 

Cell wall Structure Peptidoglycan present in the cell walls of all bacteria Composed of n-acetylmuramic acid (NAM) and n-acetylglucosamine (NAG) which alternate to form a glycan chain Tetrapeptide chains form to connect NAM molecules in a second layer L-alanine D-glutamic acid Diaminopimelic acid- chemical unique to bacteria D-alanine

Cell wall Structure : 

Cell wall Structure Gram Positive Bacterial Cell Walls Thick layer of peptidoglycan with peptide interbridge: o 40-80% dry weight of cell o Up to 30 layers of glycan chains Contains teichoic acids o Chains of either ribitol phosphate or glycerol phosphate with sugars or D-alanine attached o Connect to the peptidoglycan molecules via a covalent bond with NAM o Lipoteichoic acids are attached to cytoplasmic membrane Are chemical signature recognized by phagocytes for immunity o Teichoic acids and lipoteichoic acids extend to outside of peptidoglycan o Have negative charges so cell wall has a negative charge

Structural unit of Peptidoglycan : 

Structural unit of Peptidoglycan

Slide 33: 

Teichoic Acid Structure

Cell wall Structure : 

Cell wall Structure Gram Negative Bacterial Cell Wall Very thin layer of peptidoglycan Most of cell wall is an outer membrane rich in lipopolysaccharides; bilayer like cytoplasmic membrane Peptidoglycan is sandwiched between cytoplasmic membrane and the outer membrane (within the periplasm)

Gram negative Bacterial cell wall structure : 

Gram negative Bacterial cell wall structure Lipopolysaccharide Lipid portion (Lipid A) o Anchors molecule to outer membrane o Fatty acids attached to a disaccharide o Causes endotoxic shock o Very powerful biological activity Sugar portion o Core polysaccharide- varies with species o O-polysaccharide- varies within species Also known as O antigen 2,000 different O Ags of Salmonella 100’s different O Ags of E. coli, E. coli O157

Gram Negative Bacterial Cell Wall : 

Gram Negative Bacterial Cell Wall Outer membrane: Outermost is lipopolysaccharide (LPS) Innermost layer is phospholipid Connected to peptidoglycan by lipoproteins Contains porin proteins- protein channels Can be molecule specific Size specific Serves as a barrier for compounds to enter cell; excludes toxins including some antimicrobials

Slide 37: 

Gram Negative Bacterial Cell Wall

Structures Internal to the cell wall : 

Structures Internal to the cell wall Cell(Cytoplasmic Membrane) Boundary between a cell and its environment Dynamic interface Changes with temperature, age, environment Flexible, phospholipid bilayer sheet Hydrophobic tails Hydrophillic heads May contain steroid- like molecules: hopanoids to stabilize structure

Cell Membrane : 

Cell Membrane Membrane Functions Separate “outside” from “inside” Regulate transport of sugars, salts, other metabolites into cell and export ofproteins out of cell Site for interaction of enzymes in pathway Responses to external stimuli

Cell Membrane:structure : 

Cell Membrane:structure Membrane Lipids Polar ends interact with water, hydrophilic Nonpolar ends insoluble in water, hydrophobic Membrane Proteins o Peripheral Loosely connected to the cytoplasmic membrane Hydrophilic nature o Integral Amphipathic- have both hydrophilic and hydrophobic portions Extend from within the cytoplasm into the exterior environment

Cell Membrane:structure : 

Cell Membrane:structure Membrane lipids

Slide 42: 

Cell Membrane structure

Functions of the cytoplasmic membrane : 

Functions of the cytoplasmic membrane

Protoplasm : 

Protoplasm Cell pool for all biosynthetic functions Mixture of sugars, amino acids, lipids & salts 70-80% water Enzymes Major structures include Nucleoid, ribosomes and reserve deposits (Inclusions)

Nucleoid : 

Nucleoid Single, long, continuous, circular Chromosome & plasmid dsDNA Vibrio cholerae has more than one chromosome Unbound by any internal membrane Usually diffuse (some supercoiling) Sometimes condensed (much supercoiling) Evidence for attachment to inner side of cytoplasmic membrane 0.6-10 million basepairs in length 1000X longer than cell if stretched out Unwinds for replication & expression not)

Nucleoid : 

Nucleoid Chromosome contains essential genes Plasmids contain genes that enhance survivability Replicate independently of chromosome Can integrate within bacterial chromosome Possibilities for genetic recombination Also circular Unattached to membranes- may be lost in propagation of cells (i.e. some progeny get plasmid, others do

Mesosomes : 

Mesosomes A large invaginations of the plasma membrane, irregular in shape. a. increase in membrane surface, useful as a site for enzyme activity in respiration and transport. b. may participate in cell replication by serving as a place of attachment for the bacterial chromosome.

Ribosomes : 

Ribosomes Sites of protein synthesis Thousands per cell Free in cytoplasm or tethered to membrane rRNA + proteins 70S (Svedberg unit is a sedimentation rate) 50s large unit and 30s small unit Difference in prokaryotic and eukaryotic ribosome (eukaryotic are 80S) allows antibiotic targeting to prevent prokaryotic protein synthesis

Inclusions : 

Inclusions Reserve concentrated deposits found in cytoplasm as Granules of organic or inorganic material that are stockpiled by the cell for future use Some are enclosed by a single-layered membrane membranes vary in composition some made of proteins; others contain lipids Often visible with light microscope. Some also called metachromatic granules used in synthesis of ATP. Corynebacterium diphtheriae contain metachromatic granules Formed for storage purposes primarily

Organic inclusions : 

Organic inclusions Glycogen polymer of glucose units stored carbon and energy source; in many bacteria Poly-β-hydroxybutyrate (PHB) polymers of β-hydroxybutyrate lipid- like, stored carbon and energy source; in purple photosynthetic bacteria eg. Mycobacterim, Bacillus, Azotobacter and spirillum Carboxysomes- contain ribulose-1,5-bisphosphate (Rubisco common name) for CO2 fixation; in cyanobacteria, thiobacilli and nitrifying bacteria

Inclusion bodies : 

Inclusion bodies

Organic inclusions : 

Organic inclusions Gas vacuoles aggregates of hollow cylindrical structures called gas vesicles, made of a single protein, impermeable to water but permeable to gases Found in cyanobacteria and some other aquatic procaryotes like anoxygenic photosynthetic bacteria, halobacteria provides buoyancy for aquatic bacteria allowing them to alter depths in water to obtain proper light intensity or oxygen levels and nutrients.

Inorganic inclusion bodies : 

Inorganic inclusion bodies Polyphosphate granules also called volutin granules and metachromatic granules linear polymers of phosphates Sulfur granules energy and electron source; in purple photosynthetic bacteria eg. Thiobacillus Magnetosomes Magnetite (F3O4) in magnetic bacteria used to orient cells in magnetic fields Eg. Aquaspirillum magnetotacticum

Inorganic inclusion bodies : 

Inorganic inclusion bodies Sulfur granules Magnetosomes

Endospore : 

Endospore Develop within vegetative cells during unfavorable growth conditions For surviving environmental extremes • Heat, drying, radiation, pH extremes • Conditions common to soil and rock environments, aquatic sediments, mud, deserts- where long periods without water are common All species with spores are Gram+ to date Most common genera: • Clostridium (tetanus, botulism, gangrene, lockjaw) • Bacillus (anthrax)

Endospore : 

Endospore Sterilization techniques must eliminate spores- some can survive an hour’s boiling Recovered from both ancient mud (>7500 years old endospore of Thermoactinomyces vulgaris) and fossilized amber- found that spores could still germinate to produce viable cells Dormant spores transformation to vegetative cells Three stages: activation, germination and outgrowth Heat-activation usually In germination, spore swells and spore coat ruptures- loses resistance Outgrowth- spore protoplast synthesizes new components and returns to vegetative cell state

Endospore structure : 

Endospore structure Differentiated into 4 distinct parts: Core: Nucleic acids, ribosome, low levels of enzyme activity, Calcium dipicolonic acid (CDPA, 15%) & low water content. Low level of metabolic activity Two wall like layers: Cortex: Surrounds the core, mainly electron light peptidoglycan Coat: Surrounds the cortex, mainly protein Exosporium: The outer most thin layer

Arrangements of endospore : 

Arrangements of endospore Central spore. Subterminal spore. Terminal spore. (d) Terminal spore with swollen sporangium.

Endospore: Heat resistance : 

Endospore: Heat resistance

Sporulation and Germination : 

Sporulation and Germination