E. Coli bacteria structure, Bacterial morphology, Microbiology

2. BACTERIA (E. Coli) – STRUCTURE
E. coli is Escherichia coli. It is a colon bacterium.
It is rod shaped, Gram negative, facultative anaerobic, motile bacteria.
It is 1.5 um broad and 6.5 um long.
It is harmless. But occasionally it attains virulence and produce enterotoxin.
It produces diseases like diarrhea, septicemia meningitis and urinary tract infections.

3. GLYCOCALYX - CAPSULE AND SLIME LAYER
It is found in most bacteria; slimy or gummy
substance that becomes the outermost layer of the
cell envelope;
a thick glycocalyx is often called a capsule
a thin glycocalyx is often called a slime layer
FUNCTION
protection from drying out
helps a cell adhere to a surface where
conditions are favorable for growth
provide protection against phagocytosis
(engulfment and destruction by cells) - a slippery
glycocalyx makes it difficult for the phagocyte to
grab hold of the bacterium.

4. CAPSULE
Capsule is the outer covering of the cell.
It is tightly attached to cell wall.
It is made up of disaccharides and polypeptides.
The bacteria contain capsule are called capsulated bacteria
with out capsule are called non-capsulated bacteria
capsulated bacteria - smooth colonies
non-capsulated bacteria - rough colonies
Functions
Protect the cell from drying
Prevent attachment of phages
Helps in attachment to surface
Give protection against antibacterial agents
Acts as anti-phagocytic
Provide immunological specificity to bacterial cells.

5. CELLWALL
It is the dense layer lying above plasma membrane.
It gives shape and rigidity to the cell
The cell wall is made up of strong fibres composed of
peptidoglycans (glycopeptides).
The peptidoglycans consists of alternating
monosaccharide units
N-acetyl glucosamine (G)
N-acetyl muramic acid (M)
The units are linked by β 1,4 linkages.
A tetrapeptide is attached to N-acetyl muramic
acid.
Peptidoglycans are cross linked. A pentapeptide bridge
links the tetrapeptides of adjacent peptidoglycans.
The interstices of peptidoglycan carries many chemical
compounds such as lipids, mucopeptides, teichoic acid,
protein, etc.

6. PLASMA MEMBRANE
Outer plasma membrane
Outer plasma membrane is present beneath the capsule. It is found
only on Gram negative bacteria. It is a unit membrane.
It is three layered membrane.
It is composed of two outer layers of phospholipids and a middle
layer of protein.
Phospholipids ha a polar head on the surface and the tails are in
the interior.
The protein components are embedded within the phospholipids.
Functions
 Serves as a barrier to lysosome
 It acts as an endotoxin.
 It bears O antigens.
 Permeable to small molecules such as nucleosides,
oligosaccharides, monosaccharide's, peptides and amino acids.
 The porins, a protein present in membrane serve as
receptors for the attachment of bacteriophages and bacteriocins.

7. INNER PLASMA MEMBRANE
 It is a unit membrane.
 It is made up of proteins and phospholipids.
 The outer two layers are phospholipids and the middle layer is protein.
Functions
 It is selectively permeable.
 It contains permeases, functioning as transporting system.
 It is the Centre of energy production.
 It is site of electron flow in respiration and photosynthesis.
 Phosphorylation occurs here. It functions as the energy plant.
 It provide a specific site for the attachment of chromosome.
 Replication starts from here.

8. CYTOPLASM
The cell membrane encloses the cytoplasm.
It is colloidal in nature.
The cytoplasm does not show streaming movement.
It contains ribosomes, mesosomes, chlorosomes, magnetosomes, etc.
Golgi complex, mitochondria, lysosomes, endoplasmic reticulum, etc. are absent.

9. RIBOSOME
Ribosomes are ribo-nucleo protein particles found in all cells.
Ribosomes are assembly shops for protein synthesis.
They are also described as protein factories. They are found in
the cytoplasm or attached to the endoplasmic reticulum.
Ribosomes were first observed by Claude in 1941 and named as
microsomes.
Palade in 1955 named them as ribosomes.
Ribosomes are spherical in shape. Bacterial ribosomes are 70S
type and eukaryotic ribosomes are 80S type.
Each ribosome consists of two sub units, namely large subunit
and a small subunit.
POLYSOME
Generally 5 or more ribosomes line up and join an mRNA chain.
Such a string of ribosomes is called polyribosome or polysome

10. RIBOSOME

11. MESOSOMES
Mesosomes are intracytoplasmic membranous
structures.
They are vesicular, convoluted or multilaminated
structures, formed of invaginations of the plasma
membrane into the cytoplasm.
They contain vesicles, tubules or lamellar whorls.
Functions of mesosomes
 It is involved in septum formation during binary
fission.
 It is involved in the export of exocellular
enzymes.
 It forms a link between the plasma membrane
and the nuclear material.

12. CHROMATOPHORES(CHLOROSOMES)
Chlorosomes are pigment bearing membranous structures.
They are in the form of thylakoids.
They are involved in photosynthesis.
They are found in photosynthetic bacteria.

13. MAGNETOSOMES
Magnetosomes are cellular inclusions present in some bacteria.
They are sensitive to magnetic field.
They help to orient(adjust, face) the cell in a magnetic cell.

14. NUCLEOID
The bacterial chromosome remains in a part of cytoplasm.
This is not surrounded by a nuclear membrane.
The nuclear material without a nuclear membrane is called nucleoid.
The bacterial chromosome is made up of a single double stranded circular DNA.

15. PLASMID
Plasmids are small, extra chromosomal, double-stranded, circular,
self replicating DNA molecules.
Almost all the bacteria have plasmids containing low copy
number (1-4 per cell) or a high copy number (10 – 100 per cell).
The size of plasmids varies from 1 – 500kb. Usually plasmids
contribute to about 0.5 – 5.0 % of the total DNA of bacteria.
On the basis of conjugative transfer plasmids are classified
into two categories. They are
Conjugative plasmids
Non conjugative plasmids
On the basis of function plasmids are classified into five
types. They are
F-plasmid, R-plasmid, col –plasmid,
Degradative plasmids and virulence plasmids

16. TYPES OF PLASMIDS
Plasmids are classified in to main types,
namely
F plasmids or sex plasmids have the
ability to transfer chromosomal genes to other
cells.
R Plasmids has the gene for resistance to
one or more antibiotics.
Col Plasmids have the ability to
synthesize a toxin called colicins.
Some plasmids are capable of integrating
with bacterial chromosome. Such plasmids are
called episomes.
DIFFERENT FORMS OF PLASMIDS
The plasmids exist in supercoiled form or
open circle or
linear duplex

17. FUNCTIONS OF PLASMIDS
Plasmids make toxins
They resist various antibiotics
They resist various environmental
factors
They use unusual chemical compounds
as nutrients.

18. FLAGELLUM
Bacteria possess one or more long unbranched appendages called flagella. They are
used for locomotion.
The flagella may be polar when it is arranged at one or both ends
TYPES OF FLAGELLUM
Monotrichous - Flagellum present at one end. Eg. Pseudomonas aeruginosa.
Amphitrichous- Flagella present at both ends.
Lophotrichous - A tuft of flagella is present.
Peritrichous - Flagella are uniformly distributed throughout the cell
Atrichous - Flagellum is absent

19. FLAGELLUM - structure
Flagellum consists of three components,
namely a basal body, a hook and a shaft. The basal
body consists of two sets of rings connected by a
rod. The rings are
M = ring (Membrane ring)
S = ring (super membrane ring)
P = ring (peptidoglycan ring)
L = ring (lipopolysaccharide ring)
The hook connects the basal body with the
shaft. The flagella are used for locomotion.

20. STRUCTURE OF A FLAGELLUM

21. PILI (FIMBRIAE)
Pili are short hair –like appendages
arising from the surface of bacteria.
They are shorter than flagella and are
also much more numerous.
They are straight and not hooked. They
are found in Gram negative bacteria.
Pili arise from the cytoplasm. They are
made up of protein subunits called pilin of
fimbrin.
The pilin subunits are arranged in a
helical manner. Pili divided into two types,
namely
normal pili and
sex pili.

22. FUNCTIONS OF PILI
They are involved in the clumping of
agglutination of cells.
They are involved in the transfer of
genetic materials.
They serve as phage receptor site.
They help in infection by attaching to
human epithelial cells.

23. Sex Pili
 Sex pili are hair –like structures present on the surface of some bacteria.
 They are longer than normal pili. They have an axial hole.
 They have a knob at the terminal end. They are determined by plasmids.
 The bacteria containing sex pili are called F+ cells. One or more sex pili are
produced by each F+ cells. The cells donot contain sex pili are called F- cells.
 Sex pili of F+ cell binds to F-cell during conjugation. DNA is passed from F+ to
F- cell through sex pili.
There are two types of sex pili. They are F- type and P -type
F – type are long and flexible 7 to 8 nm in diameter.
P- type pili are shorter than F- pili. They are rigid, with a diameter of 8 -
12 nm.