2. INTRODUCTION
Bacteria are single-celled prokaryotes ubiquitous in
nature.
They can be found in different types of environments.
The bacteria contains a well-developed cell structure,
which is responsible for its biological structures and
pathogenicity.
Many structural features are unique to bacteria and are
not found among archaea or eukaryotes.
bacteria may exist as free-living organisms, symbiosis
with other organisms, as parasitic organisms that can
cause harm and disease in their hosts.
3. CELL MORPHOLOGY
The most elemental structural property of bacteria is
their morphology (shape).
The common examples are:
Coccus (circle or spherical)
Bacillus (rod-like)
Coccobacillus (between a sphere and a rod)
Spiral (corkscrew-like)
Filamentous(elongated)
Cell shape is generally characteristic of a given
bacterial species, but can vary depending on growth
conditions.
5. The size of bacterial cells is different according to their
species.
Normally cell size between 1µm to 100µm.
E.Coli cell size – 2µm to 6µm in length and 1.1µm to
1.5µm in width.
Spirochetes- 500µm
Oscillatoria- 7µm
SIZE OF BACTERIA CELLS
7. Bacterial cells mostly two types.
Gram Positive bacterial cell
Gram negative Bacterial cell
TYPES OF BACTERIAL CELL
8. This group of bacteria is to retain the primary stain
(Crystal violet) during Gram staining (giving a positive
result).
The cell-wall of Gram positive bacteria consists
of Peptidoglycan.
The cell wall also consists of molecules known as
teichoic acids (polyol phosphate polymers).
Gram positive bacteria have lipid content makes up
less than 5 percent of the cell wall.
Here, these molecules play the role of anchoring the
membrane.
Gram Positive bacterial cell
9. These bacteria are do not retain the primary stain and
thus appear red with counter stain (safranine) when
viewed under the microscope.
Gram negative bacteria are also well distributed in
different environments.
Gram negative bacteria also contain the thin
peptidoglycan (2-4nm) polymer in their cell wall.
It's composed of long glycan that are cross-linked by
peptide molecules.
This composition serves a number of functions including
protecting the bacterial cell from lysis.
Gram Negative bacterial cell
10. Gram negative bacteria has the presence of different
forms of a complex macromolecule known as
lipopolysaccharide (LPS).
They are particularly important for bacteria in that they
contribute to the pathogenesis of the organisms.
The other components of Gram negative bacteria
include:
Cytoplasmic membrane
Mesosomes
Cytoplasm
Nucleoid
Endospores
11. CELL WALL
Bacteria have a rigid cell wall.
The cell wall is an essential structure that protects the cell
protoplast from mechanical damage and from osmotic
rupture or lysis.
Cell wall made of porous, rigid material such as murein,
the component of bacterial cell walls.
Murein is a unique type of peptidoglycan, a polymer of
disaccharides (glycan) cross-linked by short chains of
amino acids (peptide).
All Bacterial peptidoglycans contain N-acetylmuramic
acid and N-acetylglucosamine which is connected by
beta 1-4 glycosidic linkage.
12.
13. In the Gram-positive Bacteria , the cell wall consists of
several layers of peptidoglycan (thick).
Teichoic acids is perpendicular to the peptidoglycan
sheets which are unique to the Gram-positive cell wall.
14.
15. In the Gram-negative Bacteria, the cell wall is composed
of a single layer of peptidoglycan (thin) surrounded by a
membranous structure called the outer membrane.
The outer membrane of Gram-negative bacteria contains
a component, lipopolysaccharide (LPS or endotoxin),
which is toxic to animals.
16. PLASMA MEMBRANE
The plasma membrane, also called the cytoplasmic
membrane.
Its main function is as a selective permeability
barrier that regulates the passage of substances into and
out of the cell.
The plasma membrane separating the cytoplasm from
the environment.
The bacterial membrane allows passage of water and
small uncharged molecules, but does not allow passage of
larger molecules or any charged substances.
17. Bacterial membranes are composed of 40 percent
phospholipid and 60 percent protein.
The phospholipids are amphiphilic molecules with a
polar hydrophilic glycerol "head" attached via an ester
bond to two nonpolar hydrophobic fatty acid tails,
which naturally form a bilayer in aqueous
environments.
The bilayer are various structural and enzymatic
proteins which carry out most membrane functions.
The arrangement of proteins and lipids to form a
membrane is called the fluid mosaic model.
18.
19. Functions of the plasma membrane
Permeability barrier
Location of transport systems for specific solutes
(nutrients and ions)
Energy generating functions, involving respiratory and
photosynthetic electron transport systems.
Synthesis of membrane lipids (including
lipopolysaccharide in Gram-negative cells).
Synthesis of murein (cell wall peptidoglycan)
Assembly and secretion of extracytoplasmic proteins
Coordination of DNA replication and segregation with
septum formation and cell division
Location of specialized enzyme system
20. Bacterial flagella are long, thin, whip-like appendages
that move the bacteria towards nutrients and other
attractants.
Flagella are free at one end and attached to the cell at the
other end.
Flagellum can never be seen directly with the light
microscope but only after staining with special flagella
stains.
Flagella are usually found in gram-negative bacilli. Gram-
positive rods and cocci also have flagella.
FLAGILLA
21. Flagella has three basic
structure:
Filament:
Extend to exterior
Made up of flagellin
protein
Hook:
Curved sheath
Connect filament to cell
Basal body:
Anchors flagellum into cell
wall and membrane
22. Arrangement and Types
of Bacterial Flagella
There are four types of flagellar arrangement:
Monotrichous: Single polar flagellum e.g. Vibrio
cholerae, Campylobacter spp.
Amphitrichous: Single flagellum at both
ends e.g. Alcaligenes faecalis
Lophotrichous: Tuft of flagella at one ends
e.g. Spirilla spp
Peritrichous : Flagella surrounding the bacterial cell.
All the members of family Enterobacteriaceae, if
motile have peritrichous flagella.
e.g. Salmonella Typhi, Escherichia coli, Proteus spp.
23.
24. Flagella Function
They help an organism in movement.
They act as sensory organs to detect temperature and
pH changes.
Few eukaryotes use flagellum to increase reproduction
rates.
Recent researches have proved that flagella are also
used as a secretory organelle. For eg., in
Chlamydomonas
25. Pilli
The pilus is a short, hair-like structure on the cell surface of
bacterial cell associated with bacterial adhesion.
It is related to bacterial colonization and infection.
Pili are composed of oligomeric pilin proteins.
They can have a role in movement.
Pili are shorter and thinner than flagella. Pili can be found
evenly around the surface of the cell, or localized to one or
both of the poles.
They are of Gram-negative bacteria, but can be found in
Gram-positive bacteria and archaea as well.
There are also pili involved in the exchange of genetic material,
called the F pili.
The pili are involved in conjugation process between two
bcaterial cells. The conjugation pilus, also called sex pilus or F
pilus. The F pilus are found on Escherichia coli.
26. Nucleoid region
The nucleoid (meaning nucleus-like) is an irregularly-
shaped region within the cell of a prokaryote.
It contains all or most of the genetic material.
The genome of prokaryotic organisms is a circular,
double-stranded piece of DNA, called genophore.
The nucleoid, also has no membrane around it.
The nucleoid doesn’t take a uniform shape and has no
specific size.
The nucleoid is mainly composed of multiple copies of
DNA with the addition of some RNA and proteins.
27. The nucleoid is essential for controlling the activity of
the cell and reproduction.
It is the site where transcription and replication of
DNA take place.
It help the formation of DNA, facilitating cell growth,
and regulating the genetic material of the cell.
Function of Nucleoid
28. Ribosomes
Bacteria have
70S ribosomes.
Ribosome consisting of a
small (30S) and a large (50S)
subunit with proteins.
Small subunit has a 16S RNA
subunit .
The large subunit is
composed of a 5S RNA
subunit, a 23S RNA subunit.
The main function is to serve
as the site of mRNA
translation and protein
synthesis.
29. Metachromatic Granules
Metachromatic granules, sometimes termed as
Volutin granules because of their colour reaction with the
dyes used in light microscopy.
It contain polymerized inorganic phosphate, an energy-rich
compound that acts as a reserve store of energy.
Polyphosphate granules display the metachromatic effect,
appearing red when stained with methylene blue.
They can also be found in the cytoplasm of Saccharomyces.
Metachromatic granules will stain pink with methylene
blue.
They are composed of complex polyphosphate, lipid, and nu
cleoprotein molecules (volutin) and serve as an intracellular
phosphate reserve.
30. Mesosomes
An organelle of bacteria
that appears as an
invagination of the plasma
membrane.
It functions either in DNA
replication and cell
division or excretion of
exoenzymes.
Mature mesosomes
formed a link between the
cytoplasmic membrane
and the nucleus of the
cell.
31. Vacuoles
Vacuoles are storage
bubbles found in cells.
They are found in both
animal and plant cells but
are much larger in plant
cells.
Vacuoles might store food
or any variety of nutrients
need to survive.
They can even store waste
products so the rest of the
cell is protected from
contamination.
It functions as storage,
ingestion, digestion,
excretion, and expulsion of
excess water.
32. Vacuoles are essentially enclosed compartments which
are filled with water containing inorganic and organic
molecules including enzymes.
Vacuoles has outer membrane called tonoplast.
Vacuoles are formed by the fusion of multiple
membrane vesicles.
The organelle has no basic shape or size; its structure
varies according to the requirements of the cell.
It maintain an acidic internal pH.
It containing small molecules.
Exporting unwanted substances from the cell.
Vacuoles also play a major role in autophagy.
33. Spores are the single-celled reproductive unit of bacteria,
fungi, algae and non-flowering plants.
Spores are units of asexual reproduction. They can produced a
new bacteria or plants.
They are able to travel over long distances.
Some bacteria also produce spores as to survive in very harsh
conditions.
A spore is a single cell surrounded by a thick cell wall for
protection.
Once the spores are formed, the organism releases them into
the environment to grow.
Spores are often formed through a process
called sporogenesis, through mitosis, or cellular
reproduction.
Spores
34.
35. Bacterial spores serve as a resting, or dormant, stage in the
bacterial life cycle, help to preserve the bacteria through
unfavourable conditions.
Bacillus and Clostridium bacteria generally produced
spores.
Spores are haploid in nature, germinate and produced
haploid gametophyte.
Spores are classify into endospore and exospore depending
on the position.
Endospore are generally produced by bacteria and exospore
are mainly produced by eukaryotes, fungi and algae.
Both have low metabolic rate and non- nutritive.
They are highly resistant.
36. Cyst
A microbial cyst is a resting or dormant stage of a
microorganism, that helps the organism to survive in
unfavorable environmental conditions.
It is a state, in which the metabolic processes of the cell are
slowed and the cell ceases all activities like feeding and
locomotion.
Unfavorable environmental conditions such as lack of
nutrients or oxygen, extreme temperatures, lack of
moisture and presence of toxic chemicals, which are not
suitable for the growth of the microbe trigger the
formation of a cyst.
37. The cyst walls of bacteria are formed by the
thickening of the normal cell wall with
added peptidoglycan layers .
Cyst is a group of cells, which come together to protect
the organism from harsh environmental conditions.
Cysts are not reproductive cells.
