Bacterial Morphology Arrangement

Robert Hooke
(1635-1703)
 English Scientist
 First to use the
microscope to observe
cells
 Coined the term “cell”

Anton van Leeuwenhoek
1632-1723
 Dutch scientist
 Invented the first
compound microscope
 First to observe
LIVING cells
 Blood cells and
protists

Robert Brown
1773-1858
 Scottish botanist
 In 1831 he was the
first person to observe
the nucleus of a cell

Schleiden & Schwann
1804-1881 1810-1882

Developing Cell Theory
1838
Schleiden
Said “all plants
are made up of
cells”
Schwann
Said “all animals
are made up of
cells”

Cell Theory Overview
1. All organisms are made of one or
more cells [Unicellular or Multicellular].
2. All cells carry on life activities.
3. New cells arise only from other living
cells.

Prokaryotic vs Eukaryotic
 PROKARYOTIC
 Simplest form
 Lack membrane
bound structures
 Lack true nucleus
 Example: bacteria
and cyanobacteria
 EUKARYOTIC
 Most common
 Possess membrane
bound structures
and a nucleus
 Found in most living
things

Sizes of Cells
 Eukaryotic are
usually larger than
prokaryotic
 Both nutrients and
wastes are
constantly entering
and exiting cells
 Vary in size and
shape

Size relationships among
prokaryotes

Bacterial Morphology Arrangement
1. Rod or Bacilli
a.Streptobacilli
b. Bacilli
2. Cocci
a. Cocci
b. Diplococci ( e.g. Neisseria meningitidis)
c. Streptococci ( e.g. Streptococcus pyogenes)
d. Staphylococci (e.g. Staphylococcus aureus)
e. Sarcina
f. tetrads ( Micrococcus species)

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Bacterial Shapes, Arrangements,
and Sizes
 Variety in shape, size, and arrangement but typically
described by one of three basic shapes:
 coccus - spherical
 bacillus – rod
 coccobacillus – very short and plump ( Brucella abortus)
 Streptobacilli ( Bacillus subtilus)
 diplobacilli
 spirillum - helical, comma, twisted rod,
 spirochete – spring-like- flexible ( Treponema pallidum)
 vibrio – gently curved ( Vibrio cholera)
 Spirilla- rigid ( Borrelia species)
 Pleomorphic : variable in shape ( Corynebacterium)

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Bacterial Shapes, Arrangements,
and Sizes
 Arrangement of cells is dependent on pattern of
division and how cells remain attached after
division:
 cocci:
 singles
 diplococci – in pairs
 tetrads – groups of four
 irregular clusters
 chains
 cubical packets
 bacilli:
 chains
 palisades

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Streptococcus sp.

Bacterial morphologies (1)

Bacterial morphologies (2)

Bacterial morphologies (3)

Bacterial Morphology Arrangement
3 Spirl
a. Vibrio
b. Spirillum
c. Spirochete

Bacterial morphologies (4)

Borrelia (spirochete)

Bacterial Cell Structures &
Functions
Pili

Bacterial Cell Structure
 Appendages - flagella, pili or fimbriae
 Surface layers - capsule, cell wall, cell
membrane
 Cytoplasm - nuclear material, ribosome,
mesosome, inclusions etc.
 Special structure - endospore

Appendages
1. flagella
Some rods and spiral form have this.
a). function: motility
b). origin : cell membrane flagella
attach to the cell by hook and basal body
which consists of set(s) of rings and rods
Gram - : 2 sets of ring and rods, L, P, S, M rings and
rods . e.g. E. coli
Gram + : S, M rings and rods .e.g. B. megaterium

Flagella
 Motility - movement
 Swarming occurs with some bacteria
 Spread across Petri Dish
 Proteus species most evident
 Arrangement basis for classification
 Monotrichous; 1 flagella
 Lophotrichous; tuft at one end
 Kophotrichous; tuft at both ends
 Amphitrichous; both ends
 Peritrichous; all around bacteria

Structure of the flagellum

c).Origin (continued)
– The structure of the bacterial flagella allows it to spin like a
propeller and thereby propel the bacterial cell; clockwise or
counter clockwise wave like motion.
– Bacterial flagella provides the bacterium with mechanism for
swimming toward or away from chemical stimuli, a behavior
is knows as CHEMOTAXIX, chemosenors in the cell
envelope can detect certain chemicals and signal the flagella
to respond.
d). structure
protein in nature: subunit flagellin ( globular protein)

Flagella movement(1)

Flagella movement(2)

2. Fimbriae and Pili
Fimbriae: Shorter than flagella and straighter ,
smaller, hairlike appendages . Only on some
gram- bacteria.
a). function: adhere. Not involve in motility.
One of the invasive mechanism on bacteria.
Some pathogens cause diseases due to this
(Antigenic characteristic). Prevent phagocytosis.

pili - sex factor. If they make pili, they are + or
donors of F factor.
It is necessary for bacterial conjugation
resulting in the transfer of DNA from one cell to
another.
It have been implicated in the ability of
bacteria to recognize specific receptor sites on
the host cell membrane.

Conjugation in E. coli

b). Origin: Cell membrane
c). Position: common pili , numerous over the
cell, usually called sex pile, 1-4/cell
d). Structure: composed of proteins which can
be dissociated into smaller unit Pilin . It
belongs to a class of protein Lectin which
bond to cell surface polysaccharide.

II. CELL SURFACE LAYER
1. Glycocalyx: Capsule or slime layer
Many bacteria are able to secrete material
that adheres to the bacterial cell but is
actually external to the cell.
It consists of polypeptide and
polysaccharide on bacilli. Most of them
have only polysaccharide. It is a protective
layer that resists host phagocytosis.
Medically important ( Streptococcus
pneumonia).

Capsule and Slime layer
 The layer is well organized and not easily washed off,
it is capsule
 Slime layer, unorganized material that is easily
removed.
 They give mucoid growth on agar plate
 B. anthracis has a capsule of poly-D-glutamic acid,
while S. pyogenes made of Hyaluronic acid.
 Function: Resistant phagocytosis, Protect against
desiccation, Attachment to surface of solid objects.

Axial Filaments
 Present in spirochetes ( Treponema
pallidum cause syphilis)
 Function is motility – gliding motility
 Bundles of fibrils that arise at the ends
of the cell

Spirochetes
 Axial filament
 Structurally similar to flagella
 Unique location under an outer
membrane

2. Bacterial Cell Wall
General structure: mucopolysaccharide
i.e. peptidoglycan. It is made by N-
acetylglucosamine and N-acetylmuramic acid.
tetrapeptide ( L-alanine- isoglutamine-lysine-
alanine) is attached. The entire cell wall
structure is cross linked by covalent bonds.
This provide the rigidity necessary to maintain
the integrity of the cell.
N-acetylmuramic acid is unique to
prokaryotic cell.

Cell walls of bacteria(2)

Cell walls of bacteria(3)

Cell walls of bacteria(4)

Cell walls of bacteria(1)

Structure of peptidoglycan(1)

Structure of peptidoglycan(2)

a). Gram positive bacterial cell wall
Thick peptidoglycan layer
pentaglycin cross linkage.
Teichoic acid (TA): Polymer of ribitol
& glycerol joined by phosphate groups
Some have peptioglycan teichoic acid.
All have lipoteichoic acid.

Function of Teichoic acids:
* Antigenic determinant
* Participate in the supply of Mg to
the cell by binding Mg++
* regulate normal cell division.
For most part, protein is not found as
a constituent of the G+ cell wall except
M protein on group streptococci

Structure of the Gram-positive
Cell Wall

(b) Gram negative bacterial cell wall:
Thin peptidoglycan
Tetrapeptide cross linkage
A second membrane structure: protein and
lipopolysaccharide (LPS).
Toxicity : endotoxin on lipid A of LPS.
glucosamine- glucosamine-long
polysaccharide- repeated sequences of a few sugars
(e.g. gal- mann-rham) n=10-20 O antigen

Structure of peptidoglycan(3)

Toxicity : endotoxin on lipid A of
lipopolysaccharide.
glucosamine- glucosamine-long
FA FA FA FA
polysaccharide- repeated sequences of
a few sugars (e.g. gal- mann-rham)
n=10-20 O antigen

Chemistry of LPS

The Gram-negative outer membrane(1)

The Gram-negative outer membrane(2)

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Atypical Cell Walls
 Some bacterial groups lack typical cell wall
structure i.e. Mycobacterium and Nocardia
 Gram-positive cell wall structure with lipid mycolic
acid (cord factor)
 pathogenicity and high degree of resistance to certain
chemicals and dyes
 basis for acid-fast stain used for diagnosis of infections
caused by these microorganisms
 Some have no cell wall i.e. Mycoplasma
 cell wall is stabilized by sterols
 pleomorphic

2. Cell Membrane
Function:
a. control permeability
b. transporte’s and protons for cellular metabolism
c. contain enzymes to synthesis and transport
cell wall substance and for metabolism
d. secret hydrolytic enzymes
e. regulate cell division.
 Fluid mosaic model. phospholipid bilayer and
protein (structure and enzymatic function). Similar
to eukaryotic cell membrane but some differs. e.g.
sterols such as cholesterol in Euk not in Prok.

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Functions of
the cytoplasmic membrane(1)

Functions of
the cytoplasmic membrane(2)

Transport proteins

Classes of membrane
transporting systems(1)

Classes of membrane
transporting systems(2)

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Bacterial Internal Structures
 Cell cytoplasm:
 dense gelatinous solution of sugars, amino
acids, and salts
 70-80% water
 serves as solvent for materials used in all cell
functions

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Bacterial Internal Structures
 Chromosome
 single, circular, double-stranded DNA
molecule that contains all the genetic
information required by a cell
 DNA is tightly coiled around a protein,
aggregated in a dense area called the
nucleoid.

The bacterial chromosome and
supercoiling

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Bacterial Internal Structures
 Plasmids
 small circular, double-stranded DNA
 free or integrated into the chromosome
 duplicated and passed on to offspring
 not essential to bacterial growth and
metabolism
 may encode antibiotic resistance, tolerance to
toxic metals, enzymes and toxins
 used in genetic engineering- readily
manipulated and transferred from cell to cell

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Bacterial Internal Structures
 Ribosomes (70 S)
 made of 60% ribosomal RNA and 40%
protein
 consist of two subunits: large and small
 procaryotic differ from eucaryotic
ribosomes in size and number of proteins
 site of protein synthesis
 present in all cells

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3. Mesosomes ( mostly in Gram +ve)
A large invaginations of the plasma membrane,
irregular in shape.
a. increase in membrane surface, which may be
useful as a site for enzyme activity in respiration
and transport.
b. may participate in cell replication by serving as a
place of attachment for the bacterial chromosome.

4. Inclusions
Not separate by a membrane but distinct.
Granules of various kinds:
* glycogen ( used as carbon source),
*polyhydroxybutyric acid droplets (PHB)
i.e. fat droplets and have Lipid inclusion
* inorganic metaphosphate (metachromatic granules or
Volutin granules) - in general, starvation of cell for almost
any nutrients leads to the formation of this to serve as an
intracellular phosphate reservoir ( Corynebacterium).

PHB

5. Chromatophores
Only in photosynthetic bacteria and blue green algae.
Prok. no chloroplast, pigment found in lamellae
located beneath the cell membrane.
Sulfur Granules: Mainly in Thiobacillus, convert H2S
to S

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IV. Special Structure
* Endospores
Spore former: Sporobactobacilli and Sporosarcinae
(Gram + cocci)- no medical importance.
Bacillus and Clostridium ( Gram + Rod) have medical
importance. Coxiella ( Gram –ve Rod) cause Q fever.
* Position: median, sub-terminal and terminal have
small water, high calcium content and dipicolinic acid
(calcium dipicolinate)
 Extremely resistant to heat, UV, chemicals etc. may be
due to many S containing A.A for disulfide groups.

• After the active growth period approaching
the stationary growth phase, a structure
called forespore develops within the cells.
• It consists of coat, cortex and nuclear
structure.
The process of endospore
formation

Negatively Stained Bacillus: (A) Vegetative Cell (B) Endospore

Dipicolinic acid

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Detailed steps
in endospore formation(1)

Detailed steps
in endospore formation(2)

Detailed steps
in endospore formation(3)

PROCARYOTIC vs.
EUCARYOTIC CELLS
Property Procaryotes Eucaryotes
Membrane-bound nucleus Absent Present
DNA complexed with histones No Yes
Number of chromosomes One > One
Nucleolus Absent Present
Mitosis No Yes
Genetic recombination Partial Meiosis
unidirectional fusion of gametes

PROCARYOTIC vs.
EUCARYOTIC CELLS
Property Procaryotes Eucaryotes
Mitochondria Absent Present
Chloroplasts Absent Present
Endoplasmic reticulum Absent Present
Golgi apparatus Absent Present

PROCARYOTIC vs.
EUCARYOTIC CELLS
Property Procaryotes Eucaryotes
Plasma membrane sterols Usually no Yes
Flagella Submicroscopic Membrane bound
(1 fiber) 20 microtubules
(9+2)
Microtubules Absent or rare Present

PROCARYOTIC vs.
EUCARYOTIC CELLS
Property Procaryotes Eucaryotes
70S (30S+50S)
80S (40S+60S)
Lysosomes, peroxisomes Absent Present
Cell walls
Ribosomes
Complex; peptidoglycan Simple; no peptidoglycan
70S (30S+50S)