unit iii- characteristics of microorganisms part ii

7/30/2019 Unit III- Characteristics of Microorganisms Part II

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Unit III- Structural characteristicsof bacteria


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2

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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unit iii- characteristics of microorganisms part ii

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