2 Morphology

7/30/2019 2 Morphology

1/43

MORPHOLOGY OF THEBACTERIA

LECTURE 2


2/43

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)


3/43

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


4/43

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


5/43
http://e/ART/150dpi/Ch04/pages/figure4_01.html


6/43
http://e/ART/150dpi/Ch04/pages/figure4_02apart1.html


7/43
http://e/ART/150dpi/Ch04/pages/figure4_02bpart1.html


8/43
http://e/ART/150dpi/Ch04/pages/figure4_02gpart1.htmlhttp://e/ART/150dpi/Ch04/pages/figure4_02dpart1.html


9/43

Structurally bacterial cells

consists of: 1. Cell membrane cell wall 2. Internal structure ribosoms, nuclear

region, granules, vesicles 3. External structure capsules, flagella,

pili


10/43
http://e/ART/150dpi/Ch04/pages/figure4_03.html


11/43

morphological characteristics of

bacteria that is used inidentification system:

1) Cell wall component 2) Slime/capsule 3) Flagella/pili/fimbriae 4) Spore/endospore


12/43

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.


13/43

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.


14/43

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.


15/43

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.


16/43

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.


17/43


18/43


19/43

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


20/43

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.


21/43

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.


22/43

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.


23/43

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.


24/43

Polar or Monotrichous Lophotrichous Peritrichous


25/43

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


26/43


27/43


28/43


29/43


30/43


31/43

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.


32/43

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


33/43


34/43


35/43

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 )


36/43

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.


37/43

mainly of the genera Bacillus (aerobicrods, facultative anaerobes), and

Clostridium (anaerobic rods); Few others include Sporosarcina (aerobic

cocci), Desulfotomaculum (anaerobic

rods, sulfate-reducers)


38/43


39/43

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


40/43

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


41/43

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


42/43

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.


43/43

Documents

2 Morphology