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MORPHOLOGY OF THEBACTERIA
LECTURE 2
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Four cellular morphology of
bacteria 1. Cocci (coccus) (a) Streptococcus pyogenes occurs as pairs of
chains. (b) pairs of tetrad, Pediococcus (c) cube-shape packets, Sarcina lutea
diplococci, pairs, Neisseria gonorrhoeae, N.meningitidis
(d) cluster of cells ( Staphyloccus aureus ) (grape-
like clusters)
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2. Rods Bacillus , E. coli single, diplobacilli,streptobacilli, coccobacilli Moraxella ,
Acinobacter 3. Filament if the rod is so many times longer
than its wide.
Myxobacteria, Myxococcus, Cytophaga 4. Spiral/helix long spiral and helically coils
rods, the spirochetes, 5-500 um long, eg.
Spirillium motile by polar flagella. Other shaped, vibriod or comma shaped, Vibrio, Star-shape, Stella square, Haloarchula
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Shape offers an advantage to the cell:
Cocci: more resistant to drying than rods Rods: More surfacee area & easily takesin dilute nutrients from the environment
Spiral: Corkscrew motion & thereforeless resistant to movement Square: Assists in dealing with extreme
salinities
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Structurally bacterial cells
consists of: 1. Cell membrane cell wall 2. Internal structure ribosoms, nuclear
region, granules, vesicles 3. External structure capsules, flagella,
pili
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morphological characteristics of
bacteria that is used inidentification system:
1) Cell wall component 2) Slime/capsule 3) Flagella/pili/fimbriae 4) Spore/endospore
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1. Cell wall component
All the members of domain Bacteria, with theexception of the genera Mycoplasma ,Ureaplasma , Spiroplasma, and Anaeroplasma
contain cell walls Gram stain. Gram stain is a method of coloring
bacterial cell wall that can give two results: 1. Red: Gram (-) ve 2. Blue: Gram (+) ve 18 hours culture is preferably used.
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What are the different in the cellwall composition of these two
classes of bacteria?
1. murein or peptidoglycan layer
composed of two sugar derivatives; N-acetylglucosamine (NAG) and N-acetylmuramic(NAM) acid and a small group of acid amino .
Gram (+) ve bacteria has a thick peptidoglycan layer compared to the Gram (-) ve bacteria and alsocontain teichoic acids,
peptidoglycan of Gram +ve comprises 90% of the cellwall and only 10% is Gram ve.
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Gram ve bacteria has an outer membranelipopolysaccharide .
The lipid and polysaccharide are linked toform specific lipopolysaccharide structure.
The cell wall of Gram (-) ve bacteriathicker 10 to 50 nm in width.
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A lipoprotein complex is found on the inner sideof the outer membrane in a number Gram ve
bacteria. It serve as an anchor between the outer membraneand peptidoglycan.
One biological property of the outer membranelayer of many Gram ve bacteria is that itfrequently toxic to animals due to Lipid A portion.Eg. Salmonella, Shigella, and E. coli.
The toxic property of the outer membrane layer of these bacteria is responsible for some of thesymptoms of infection which these bacteria
brings- fever, dilates of blood vessel.
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Gram (+)ve bacteria, with its thick peptidoglycan traps the stain while thin peptidoglycan in Gram (-) ve bacteria celldoes not.
Gram ve has periplasmic space (gap), anactive area of cell metabolisms. It contains peptidoglycan, digestives enzymes,transport protein that destroy harmfulsubstance and transport metabolites intocytoplasm.
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Differences Between Gram-positive And Gram-negative
Bacterial Cell Walls
Gram-positive wall Gram-negative wall
Peptidoglycan Thick layer Thin layer
Peptidoglycantetrapeptide
Most contain lysine All containdiaminopimelate
Peptidoglycan crosslinkage
Generally viapentapeptide
Direct bonding
Teichoic acid Present Absent
Teichuronic acid Present Absent
Lipoproteins Absent Present
LPS Absent Present
Outer Membrane Absent Present
Periplasmic Space Absent Present
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2. Archaeal Cell Walls:
Archaeal cells have more variations intheir cell wall chemistries, and some donot contain cell walls (eg Thermoplasma)
3. Eucaryal Cell Walls: Cell walls of algae have a variety of
different cell wall types and includecellulose, calcium carbonate, silconedioxide, proteins and evenpolysaccharides.
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2. Glycocalayx, Capsules, SlimerLayers & S layers:
Glycocalyx varies in different species: Capsules:
Are thick & rigid structures which exclude stain.
Adhere externally to the to cell walls Negative stain allows capsules to be observed. Chemically polysaccharides. Found in pneumonia causing
pathogens such as Streptococcus pneumoniae, Haemophilusinfluenzae & Klebsiella pneomoniae.
Chemically D-glutamic acid found in some Bacillus sp. Capsulated variants of a species are pathogenic whereas non-
capsulated variants of the same species are non-pathogenic.Capsules protect against phagocytosis by human white bloodcells.
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Slime layers: Similar in composition to capsules but are not
as tightly bound to the cell wall. Protects cells against dehydration and a loss of
nutrients. S layer: Some bacteria have a crystalline protein layer
called a S layer. Found outside the cell walls of some species of
Gram-negative, Gram-positive Bacteria, andoutside the cell membranes of some Archaea . Function is unknown.
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3. Flagella/pili/fimbrieae
Function as motility The flagella are so thin (20 nm) that a single
flagellum can never seen directly using thelight microscope but only after staining withflagella stains (basic fuchsin, with tannic
acid). It can be seen clearly with EM by negative
staining.
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Polar or Monotrichous Lophotrichous Peritrichous
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Types of flagella orientation
1. Polar attached to one or both end of the cell.Can be single or numerous.
Monotrichous (single) Eg. Pseudomonas spinosa , polar, Vibrio
Amphitrichous two flagella, one at each end.Spirillium
Lophotrichous - If a turf of flagella arise at one end of the cell or both ends, (lopho = turf),trichous = hair Peritrichous flagella grow from many surface of on
the cell (peri-around)- Proteus mirabil is, Salmonella
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Bacterial flagella are composed of proteinsub units, call flagellin .
The amino acid of flagellin are lower amounts of sulphur and aromatic aminoacids, but rich with aspartic acid and
glutamic acid.
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Fimbriae
Not all bacteria posses fimbrae -- it is aninherited trait
Arise from the cytoplasmic membrane or justbelow the membrane
Can be mistaken for flagella but are notinvolved in motility
Much shorter and more numerous than flagella Adhesion (dnh cht)functions which enables cellsto form a pellicle (lp mng)on liquid (cht lng) surface
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Pili
Similar to fimbrae but longer and fewer;sometimes only one per cell
Three functional types of bacterial pili: Act as receptors sites for some attachment of
some phages ie phage infection
Act as sex pilus for bacterial conjugationprocesses (F aka Fertility pili of E. coli ) Attachment for pathogenic bacteria to
human tissues ( Neisser ia gonorrhoeae )
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4. Spore
The spore have unique characteristics:resistance to heat, drying, radiation, acids
and chemical disinfectants The present of dipicollinic acid (DPA)
together with calcium ions in the core of the
spore cause the unusual heat resistance tothe bacteria.
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mainly of the genera Bacillus (aerobicrods, facultative anaerobes), and
Clostridium (anaerobic rods); Few others include Sporosarcina (aerobic
cocci), Desulfotomaculum (anaerobic
rods, sulfate-reducers)
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Spore
Size Larger (distends the cell) or smaller than the cell
Shape Cylindrical (hnh tr) Ellipsoidal (hnh elp) Spherical (hnh cu)
Location Central Terminal Sub-terminal
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Cells with endospores (ni bo t)can beidentified by spore-staining B. megater ium, an aerobe: Small cylindrical
sub-terminal spores C. tetani , an anaerobe: Large (distend)
spherical terminal spores Heat resistance
Spore structure
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Spore structure Spores are formed during unfavourable
growth conditions & germinate (ny mm)under
favourable conditions The spore can be differentiated into 4 parts:
Core: Nucleic acids, ribosome, low levels of enzyme activity, Calcium dipicolonic acid(CDPA) & 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
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The location (s xnh) of spore is one of thecriteria in the bacterial classification:
terminal, subterminal, central, paracentral. The shape of the spore: oval, round,
ellipsoidal etc.
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