Bacterial cytology
-
Upload
salman-ali -
Category
Education
-
view
393 -
download
2
Transcript of Bacterial cytology
BACTERIAL CYTOLOGY
CELL WALLWHY STUDY-Determines shapeProtects cellProtection from toxic substancesSite of action for antibiotics
LOCATION-Outermost, rigid layer
TYPES-based on Gram staining
• Gram Positive, purple colour• Gram Negative, pink colour (Christian Gram-1884)
Structural differences between G+ve & G-ve cell wall
• 20-80% nm thick peptidoglycan (murein)
• 2-7% nm thick peptidoglycan
PEPTIDOGLYCAN STRUCTURE- G+ve1. Amino sugars N acetyl glucosamine & N acetyl muramic acid(NAG & NAM)2. Protein3. Techoic acid
TECHOIC ACID
Mesh structure of peptidoglycan
GRAM NEGATIVE CELL WALL
BLP( Braun’s lipoprotein)• Braun's lipoprotein found in some gram-negative cell
walls• the most abundant membrane proteins• It is bound by a covalent bond to the peptidoglycan layer• and is embedded in the outer membrane by its
hydrophobic head • BLP tightly links the two layers and provides structural
integrity to the outer membrane.
• Braun's Lipoprotein consists of phospholipids and Lipopolysaccharide.
Gram Negative Cell Wall-chemical compostion
• Lipopolysaccharide (LPS)Large, complex molecule with lipid & carbohydrate1. Lipid A2. Core polysaccharide3. O side chains
Functions of LPS• Give negative charge to the surface• Helps in attachment• Stabilize the membrane• Create a permeability membrane• Prevent entry of toxic substances• O side chain protects bacteria• Lipid A is toxic (endotoxin)- causes serious
septic condition in the body
Functions of LPS• Outer membrane is more permeable
than pm due to porins• Porins are proteinic in nature, tube
shaped, allows passage of molecules smaller than 600-700d• For larger molecules carrier proteins
are there
Periplasmic space in bacteria
Periplasmic space in bacteria• Gram Positive• Small• Fewer proteins• Proteins present,
attached to plasma membrane
• Exoenzymes- degrade polymeric nutrient
• Gram Negative• Wide (30nm-70nm)• More proteins• Hydrolytic enzymes,
transport proteins• Electron transport
proteins• Proteins for ppd syn• Modify toxic compd
COMPONENTS EXTERNAL TO CELL WALL
Capsule, Slime layer and S layerCapsule- chemical structure-1. Polysaccharide2. Protein3. Polysaccharide-Protein
GLYCOCALYX(capsule,slime)
• When the layer is well organized and not easily washed out
• When it is a zone of diffuse, unorganized material that is removed easily
Capsule under the microscope
Functions of Capsule
• Resist phagocytosis
• Storing water, prevents from desiccation
• Helps in attachment
S layer
• External to cell wall
Functions of S layer1. Protection against -• ions and pH fluctuation• Adverse surroundings2. Maintains shape3. Promotes adhesion4. Adds the property of virulence
Pilus (pili, fimbriae)• Short, fine, hair like appendages• Visible under electron microscope
only• One cell may have 1000 of pili• Slender tube • 3-10nm in diameter, several
micrometer in length
PILI
PILI
Pilus
Helically arranged pilin proteins
Chemical composition-Protein- PILIN
Functions of Pili• Attachment-rock surface, host cell
• Some may help in motility eg type IV- jerky motility up to several mm
• Gliding motility eg. Myxobacteria
• conjugation
Flagella(flagellum)• Thread like locomotory organelle• Extending outward from the cw and pm• Slender, rigid structure• 20nm across and 15-20micrometer long• Stained and can be seen under
compound ms• Ultrastructure under electron ms
Arrangement of flagella
Ultrastructure of flagella
Under TEM
Ultra structure of flagella
Flagellar ultrastructure
Three parts1. Filament2. Basal body3. hook
Ribosome
Ribosomes Location- cytoplasm and some attached to pmcomplex structureComposition- protein and ribonucleic acid (RNA)Parts- 50s and 30s(s- svedberg unit)Function- protein synthesisFolding of protein- by special protein called chaperone
Ribosome contd.
Size- 14-15nm by 20nmMol wt.-2.7 million
The nucleoid
The most striking feature
no nuclear membraneLocated in an irregularly shaped
region called nucleoid
Other namesNuclear body, chromatin, nuclear
region
Forms
1. Double stranded DNA(deoxyribonucleic acid)2. Linear chromosome3. Some have more than one chromosome
• A chromosome is a structure of DNA, protein, and RNA found in cells.
• It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences.
• Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.
• DNA encodes most or all of an organism's genetic information;
• some species also contain plasmids or other extra chromosomal genetic elements.
Electron micrograph
Chemical analysis• 60% DNA• 30% RNA• 10% Protein• E.coli-DNA circle-1400µm230-700 times longer than the cellLooped and coiled efficientlyNo histone protein
Exceptions- Perillulla & Gemmata
Gemmata
plasmid
Extra chromosomal DNA material
PlasmidExamples- bacteria, fungi, yeast.Small, double stranded DNA moleculeExist independent of chromosomeLinear and circularFew genes –less than 30Not essential for survivalSelective advantage
PlasmidReplicate autonomouslySingle copy produces one copy per cellAble to integrate into the chromosome and gets replicated – episomeSometimes lostThe loss of plasmid- curing
Curing agents• UV and ionizing radiation• Thymine starvation• Antibiotics• Growth above optimal
temperature
Types of Plasmidstype host function
Fertilty factor E.coli conjugationMetabolic plasmids
E.ColiRhizobium
Lactose degradation& symbiosisNitrogen fixation
R plasmid Pseudomonas Resistance to antibiotic
Col plasmid E.coli Colicin production
Virulence plasmid
E.coli Entrotoxin, siderophore
Cell membrane• Retains cytoplasm• Selective membrane• Prevents loss of essential
components• Transport system•Waste excretion• Protein secretion
Plasma membrane-functions
• Location for respiration, photosynthesis, synthesis of lipid and cell wall constituents• Has receptor molecule to detect and
respond to chemicals in the surrounding• Essential for the survival of bacteria
Fluid Mosaic Model
Fluid Mosaic Model of Singer & Nicolson
• Bilayer phospholipid (amphipathic)• Proteins float within• 5-10 nm thickness• Polar hydrophilic head• Long non polar hydrophobic end• Proteins-peripheral-20-30%,integral-60-80%• No cholesterol but hopanoids
Internal membraneTubule ,vesicle, lamellae
Cyanobacteria-infoldings are complexSpherical & flattened vesicle, tubular membranes
Inclusion structuresCarbon storage polymers
1. Poly-β-hydroxybutyric acid
1. PHB
Length:C3-C18
PHBSynthesis when carbon is in excess and used for biosynthesis and to make ATPPHB are referred to as poly-β-hydoxyalkonate(PHA)2. glycogen- polymer of glucoseStore house of carbon and energy
Polyphosphates
Polyphosphate contd
Functions- source of phosphateUsed as sources of phosphates for nucleic acid and phospholipid biosynthesis Note- phosphate in the environment is limited
Sulfur Granules
Elemental sulfur accumulated inside the cell
Sulfur
• Oxidize reduced sulfur(H2S)
Magnetosomes
Magnetosomes
• Some bacteria can orient themselves within magnetic field because of magnetosomes- magnetotaxis
• These are intracellular particles• Iron materials• Impart magnetic dipole on a cellFunctions-not knownMay be guiding bacteria towards magnetic field deep in aquatic envt. Where oxygen level is low
Magnetosomes• Surrounded by a membrane
containing phospholipid, proteins, and glycoprotein• Proteins act as chelating agents• Square to rectangular in shape to
spike shaped
Gas vesicle• Planktonic- those live in floating state• Because of gas vesicles• These structure confer buoyancy on cell• Eg. Cyanobacteria also called
BGA(bloom)• Purple and green sulfur bacteria• ArchaeaNote- Eucaryotes don’t have these structure
bloom
bloom
General structure• Spindle shaped filled with gas• Made up of protein• Hollow yet rigid• Variable length and diameter• 300nm-1000nm by 45nm-120nm• Number-few to 100 per cell• Membrane made up of protein, 2mm thick• Impermeable to water and solute but
permeable to gas
Gas vesicle contd.• Clusters of vesicles- gas vacuole• Can be seen under light microscope and TEM
Molecular structure• Major gas vesicle protein-GvpA- small,
hydrophobic and rigid(97%)• Minor protein-GvpC
Other inclusion
• Cynophysin and granules- equal amount of arginine and aspartic acid
• Store extra amount of nitrogen
Carboxysome present in photosynthetic bacteriaPolyhedral, 100nm in diameter, contains enzyme ribulose 1, 5 biphosphate carboxylase(Rubisco)
Endospore
Endospore• Endo-within• Enable cells to endure difficult time-Temperatures, drying, nutrient depletion etc.Dormant stage of bacteria-Used for dispersalExamples-Bacillus, Clostridium
Electron micrograph of endospore
Schematic presentation of endospore
Endospore formation and germination
Activation- Use of elevated temperatureGermination-Specific nutrient like alanineOutgrowth
Three stagesActivation- endospores get ready for germinationGermination- rapid process, spore loses its refractibilityOutgrowth-swelling due water up take, synthesis of new RNA, proteins &DNA.
characteristics• Dipicolinic acid in core (with calcium)in
core (10%)- reduces the water content of core.• Endospores become dehydrated1. Increases heat resistance2. Makes cells resistant to chemicals3. Keeping enzymes inactive in the core
characteristics• pH one unit lower than vegetative cell• High level of SASPs(small acid soluble
proteins)1. Bind tightly to DNA in the core –protection
from UV, desiccation, and dry heat(DNA changed from B form to the compact form A which is more resistant to mutation, denaturing effect of dry heat)2. Carbon and energy source
Difference between vegetative cell & endospore
Vegetative cell Endospore