unit iii- characteristics of microorganisms part ii
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Unit III- Structural characteristicsof bacteria
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Introduction
Bacteria are microscopic, unicellular, Prokaryotic organisms.
Ehrenberg- Bacterium
Bacteria are widely distributed. It found in soil, air, water, and
living bodies. Some bacteria cause diseases for animals and plants.
Some bacteria live in our bodies as normal flora which
harmless.
Normal Flora Pathogens
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Major Features of Bacteria
Unicellular , Some as colonies
Prokaryotic
Form- Rods, spheres, spirals/filaments
Cell Cell envelope- capsule- cell wall plasma membrane.
Nuclear material Nucleoid,
Extra chromosomal DNA Plasmid
Cell organelles ribosomes, mesosomes
Appendages: Flagella, pili.
Gram positive/gram negative
Nutrition
Binary fission
Endospores
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Only two types of cells are produced by all living
organisms on earth. Prokaryotes (pro. or primitive nucleus) do not have a
membrane bound nucleus eubacteria (true bacteria)
archaebacteria (ancient bacteria)
Eukaryotes (eu, or true nucleus) have a membranebound nucleus Algae
fungi
protozoa plants
animals
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Comparison of prokaryotic and Eukaryotic cells
(based on Prescott,1996)
Character Prokaryotes EukaryotesOrganisation of Genetic
material:
True Membrane
DNA Complex with Histone
Number of Chromosomes
Introns in genes
Nucleolus
Mitosis
-
-
One(besides plasmids)
Rare
-
-
+
+
More than one present
Present
+
+
Genetic Recombination Unidirectional transfer of DNA Meiosis and Fusion of gametes
Mitochondria - +
Chloroplast - +
Plasma Membrane with Sterol Absent except
mycoplasma&methanotrops
+
Flagella Sub-Microscopic ,one fibre Microscopic, 10 microtubules
in 9+2 pattern
Endoplasmic Reticulum - +
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Comparison of prokaryotic and Eukaryotic cells
(based on Prescott,1996)
Character Prokaryotes Eukaryotes
Golgi Appratus - +
Cell Walls
Except Mycoplasma and
archeobacteria
Complex with peptidoglycom Simple, lack peptidoglycon
Simpler Organelles
Ribosomes
Lysosomes
Microtubules
Cytoskeleton
70S
-
-
-
80 s Except in Mitochondria
and Chloroplast
+
+
+
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Prokaryotes
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Size,shape and arrangement of
bacterial cells
Small ( Approximately 0.5 t0 1.0 m in diameter)
Surface area/volume ratio
Diameter of
sphere m
Surface Area,
2m
Volume m3 Surface
Area/Volume,
m-1
1 m 3.1 0.52 6
1,000 m 3.1X10 6 5.2X108 0.006
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Size Bacteria 0.1 to 60X6 m in size
Bacilli - 5X0.4-0.7 m Pseudomonas 0.4 0.7 m diameter, 2-3 m length
Micrococci about 5 m
Bacteria Diseases Length(m )
Clostridium botulium Food poisoning 3.8
Clostridium tetani Tetanus 2-5
Coyrnebacterium
diptheriae
Diphtheria 1-8
Mycobacterium
tuberculosis
Tuberculosis 0.5-4
Salmonella typhii Typhoid 0.5-4
Streptococcus
peumoniae
Pneumonia 1.25
Staphylococcus sp. Boils 0.8
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coccus bacillus spirillum
coccusspirillumbacillus
Shape ?
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Shape and arrangement
ShapeRigid cell wall
Spherical- Cocci
Straight rods/helically curved rods- Bacilli/Spirilla
Pleomorphic Arthrobacter
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Ex: Streptococcus Ex: Lactobacillus Ex: Spirillium
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Morphology of Microbial Cells
Shape: Spherical or Ovoid
Single cellsMicrococci
Pairs - Diplococci
Cluster Staphyloccocci
Chains - Streptococci
Cubical groups Sarcinae
Rod-Shaped Bacilli
More oval - Coccobacilli
Chain Streptobacilli
Spiral Rigid- Spirilla
Flexible Spirochaetes
Curved Vibiro
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Arrangement
Coccus forms:
Diplococcus
Strepto coccus
Tetracocci
Straphylococci
Sarcinae
Forms of Bacillus:
Monobacillus
Diplobacillus
Streptobacillus
Coccobacillus
Forms of Spirilli:
Vibroid
Helical
Other forms:
Pleuromorphic
Trichomes
Palaside
Hyphae
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Structure of Bacteria
All cells have 3 main components: DNA (nucleoid)
genetic instructions
surrounding membrane (cytoplasmicmembrane)
limits access to the cells interior
cytoplasm, between the DNA and themembrane
where all metabolic reactions occur
especially protein synthesis, which occurs onthe ribosomes
Bacteria also often have these features: cell wall
resists osmotic pressure flagella
movement
pili attachment
capsule protection and biofilms
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Structure of Bacterial Cell
Capsule: Extracellular polymeric substances capsule/glycocalyx envelope-detected by negative staining- gelatinous polymer
Microcapsule
Composed of Polysaccharides/polypeptide homopolysaccharides -
heteropolysaccharides.
Slime Layer
Sheath
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Functions of Capsule
Protection against temporary drying by binding water molecules
prevent the attachment of Bacteriophages
Protects bacterial cells against desiccation, maintains viscosity and inhibits the
movement of nutrients from the bacterial cells Survive in natural Environment
Antiphagocytic -Inhibit engulfment of pathogenic bacteria by WBCs-contributeto invasive or infective ability-virulence
Source of energy
Attachment of Bacteria to surfaces eg. Streptococcus mutants dental cariessecretion of water-insoluble capsular glucan.
If capsules composed of electrical charge- uronic acid promote stability ofbacterial suspension preventing the cells from aggregating and settling out-because cells having similar charged surface surfaces tend to repel oneanother.
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Prosthecae and stalks
Prosthecae : Semi rigid extension of cell wall and cytoplasmic membrane
diameter less than that of a cell- aerobic fresh and marine.Eg. Caulobacter,
Stella andAncalomicrobium.
Increases surface areaabsorption of nutritientsadvantageous in dilute
environments end of prostheca form new cell (bud)- adhesive substances-aids in attachment
stalks : Gallionella or planctomyces-aids in attachment of the cells to surfaces
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Structure of Bacterial Cell
Flagella :Hair like,helical appendages protroude/emerging from cell
wall motility- thinner than eukaryotes -0.01 to 0.02 m diameter
polar/lateral .
Number and positions vary
Monotrichous - V.cholerae
Lophotricus - Spirillum
Amphitrichous - Aquaspirillum serpens
Cepalotrichus - Pseudomonas
Peritrichous Proteus vulgaris
Atrichous - Lactobacillus
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Flagellar arrangements
A. Monotrichous
B. Lophotrichous
C. Amphitrichous
D. Peritrichous
E. Atrichous
http://images.google.com/imgres?imgurl=http://www.helalia.com/vb/uploaded/4_flagella.png&imgrefurl=http://www.helalia.com/vb/showthread.php?p=81375&usg=__lb4Nbu8PqpnpaEafEDn8VxjDofA=&h=471&w=400&sz=30&hl=en&start=3&itbs=1&tbnid=15zl3VZ7Sn4vRM:&tbnh=129&tbnw=110&prev=/images?q=flagellar+arrangements&hl=en&gbv=2&tbs=isch:1 -
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Monotrichous Lophotrichous
Amphitrichous Peritrichous
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Structure of Flagella
Basal Body- Associated with cytoplasmic membrane and cell wall.
Hook
Helical filament
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Functions of flagella
Bacterial Motility
Deflagellation renders the motile cells immobile.
Rotation
clockwise/anticlockwise
Capacity to alter both direction of rotation/speed.
Distinct change in direction Flagella Movement
Spirocheatial movement
Gliding movement
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Swimming motility without flagella
Gliding motility
Bacterial Chemotaxis
Phototaxis
Magnetotaxis
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Pili / Fimbriae
Pile and Fimbriae- Hair like appendages-Gram negative bacteriae.g.Enterobacteriaceae,pseudomondaceae and caulobacter.
Eukaryotic cells lack pili
Plili Governed genetically by plasmid-3-5
Fimbriae-1000-Gram positive bacteriaCornebacterium renale
(i) Classes of Pili:
Common pili and sex pili
Ottow 1975 -6 groups
(ii) Structure:
Appendages
originate from cytoplasm
100% protein fimbrlin/pilin-163 amino acidsm.w. 16,000 daltons Sex pili- helical tubules-repeating protein units-filamentous structure sex factors
F factor, Col I, R
Receptor sites
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Functions of Pili/Fimbriae
Fimbriae adhesive properties-
Fimbriae agglutinate the blood cells such as
erythrocytes,leucocytes,eptithelial cells etc.,
Fimbriae-Antigenic properties act as thermoliable nonspecefic
agglutinogen.
Fimbriae affect metabolic activity
Phage receptor
Transfer of genetic material -Sex pili: Conjugation tube
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The Cell wall
Rigid & complex beneath capsule external to the plasma membrane.
Responsible for characteristic shape.
Protects plasma membrane-other cytoplasmic inclusions from adverseenvironment.
Protects bacterial cell from bursting when the osmotic pressure of cytoplasm
is higher than that of out side of cell wall.
Support for the attachment of flagella
Rescues the cells from antibodies and harmful chemicals.
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The Cell wall
Cell wall of Gram-negative bacteria is comparatively thinner than that of
gram positive bacteria- similar-gram negative archaeobacteria-chemical
composition of cell wall of archaeobacteria differs from eubacteria.
Cell wall contributes a significant portion of the dry weight of the cell.
Essential for growth and divisions.
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Structure and chemical composition
Peptidoglyconsometimes murein-insoluble-porous-cross-linked
Bag- shaped macromolecule
Polymer of N-acetyl glucosamine, N-acetyl acetyl muramic acid,L-
alanine,D-alanine, D-glutamate, and diaminoacid. Arecheobacteriaproteins, glycoproteins or polysaccharides.
Methanobacteriumpseudomurein.
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Structure and Chemical Composition
Peptidoglyconalternating monosaccharide units of N-
acetyl glucosamine(NAG) and N-acetyl muramic
acid(NAM).
Two units linked by1, 4 linkages.
A tetrapeptideattached to N-acetyl muramic acid(NAM).
Peptidoglycon cross linked- pentapeptide links the
tetrapeptides of adjacent peptidoglycons.
The intersticeslipids, mucopeptides, teichoic acids,
protein.
Walls - Bacterial antigens
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Structure and Chemical Composition
Peptidoglycon/Murein -Insoluble, porous, cross-linked
polymer.
Walls of Archaeobacteria
Walls of Gram-Positive bacteria
Walls of Gram-negative Eubacteria
Molecular surface Arrays
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Walls of gram positive and negative
bacteria Gram Positive:
Greater amount of peptidoglycon.
50% or more dry weight.
Streptococcus pyogenes- polysaccharides- cross linked withpeptidoglycon.
Staphylococcus aureus & Streptococcus faecalis- Teichoic acids-
covalently linked to peptidoglyconprotect from thermal injury.
Little lipid
Mycobacterium (mycolic acid) and Corynebacterium- Rich in lipids
b
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Gram positive bacteria
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Walls of gram positive and negative
bacteria Gram Negative
More complex.
Outer membrane- surrounds a thin underlying layer of peptidoglycan- impermeablebarrier.
Rich in lipids.
Outer membrane-anchored to the underlying peptidoglyconBrauns lipoprotein. Membrane- Bilayered- Phospholipids,proteins and lipopolysaccharide (LPS)- Toxic-
endotoxin.
Composed of three covalently linked parts- Lipid A, Core polysaccharide and O antigen.
Allow smaller molecules- nucleiosides,oligosacharides,monosaccharides, peptides,aminoacids pass across.
Channels in special proteins- Porins.
Porins are sepcific- some allow certain essential large molecules to penetrate eg vitaminB12-many serve as receptors-attachment bacteriophages and bacteriocins.
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Gram negative bacteria
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Gram Positives and Gram Negatives: Key Differences
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Gram Positives and Gram Negatives
Examples of Gram positive Bacteria:
Streptococcus pyogenes - causes strep throat
Staphylococcus aureus - causes skin infections and may be responsible for boils
Examples of Gram Negative Bacteria:
Treponema pallidum - causes syphilis
Escherichia coli - may cause severe gastrointestinal problems
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Molecular surface Arrays
Both gram positive and negative is coveredmosaic layer of protein
subunits.
Protection functiongram negative bacteriapredatory bacteria-
bdellovibros
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Difference between cell walls of Gram-
Positive and Gram-negative bacteriaCharacter Gram-Positive Gram-Negative
Grams Stain Retain crystal
violet and appear
dark violet
Pass crystal violet
and counter
stained by
safranine -appear
red.
Outer membrane Absent Present
Peptidoglycon Several layers
thick
Thin-single layer
Lipids and Proteins Low High
Lipopolysaccharides Absent High
Teichoic acid Mostly present Absent
Periplasmic Space Absent present
Flagella Contains 2 rings in
basal body
Contains 4 rings in
basal body
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Functions of cell wall
Structural integrity
Cell envelope acts as barrier
Matrix proteins acts as receptor sites
O-antigen- determines antigenic specificity of -negative
bacteria
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Structures Internal to the cell wall
Cytoplasmic membrane
Protoplasts
Spheroplasts
Membranous Intrusions and Intracellular membraneSystems.
Cytoplasm- Ribosomes, DNA and fluid portion.
Cytoplasmic inclusions and vacuoles volutin/
metachromatic granules Nuclear Material
Plasmid
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Cytoplasmic membrane /plasma
membrane 7.5 nm thick - Phospholipids and proteins-phospholipds bilayered
integral proteins- peripheral proteins
Lipid matrix has fluidity
Hydrophobic barrier-contains enzymes involved in respiratorymetabolism synthesis of cell wall and capsular components- -
important functional structure.
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Cytoplasmic membrane /plasma
membrane Outer plasma Membrane:
Gram negative bacteria - Fluid mosaic model phospholipid
Barrier to lysozyme
Endotoxin
O antigens
Permeable to small molecules
Porins- receptors.
Plasma membrane (inner):
Lipid bilayer-fluid mosaic structure Selective permeablepermease- transport system- energy production
centrephosporylation specific site for attachment of chromosomeReplication.
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Functions of plasma membrane
Transport by permease
Enzyme Biosynthetic pathways-synthesize different components-
peptidoglycon,teichoic acids, polysaccharides, lipopolysaccharides
&phospholipids.
Attachment site-bacterial chromosome and plasmid
Respiratory activity
Permeability barrier
Selective permeability
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Cytoplasm
Colloidal
No streaming movement
Ribosomes Protein synthesis , 70S, - polyribosomes
Mesosomes intracytoplasmic membranous structurescentralmesosomes and peripheral mesosomes.
Functions: helps in septum formation
DNA replication
distribution of DNA top daughter cells
Transport of exocellular enzymes-pencillinase
Link between plasma membrane and nuclear material
Chromatophores: Photosynthetic bacteria-pigment bearingphotosyntheis.
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Cytoplasmic inclusions and vocules: Volutin granules-metachromatic granules - aerobic bacteria Poly-
hydroxybutyrate-carbon and energy reserve-glycogen-gas vacuoles
Magnetosomes
Nucleoid
Plasmid
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Bacterial Reproduction:
Binary fission
Budding
Fragmentation
Endospore formation
Conidiospore.
Recombination:
Conjugation Transformation
Transduction
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Spores and Cysts
Endospores
Exospores
Conidipsores and Sprangiospores
Cysts.
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Nutritional Types
Autotrops
Photoautrophs and chemoautotrophs
Heterotrophs:
Parasitic Saprophytic
Symbiotic
Photoheterotropic
Chemoheterotropic Bacterial Respiration
Aerobic, anaerobic and facultative
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