2. WHAT IS BACTERIA?
•Bacteria are single-cell organisms that are neither plants nor
animals.
•They usually measure a few micrometers in length and exist
together in communities of millions.
•A gram of soil typically contains about 40 million bacterial cells. A
milliliter of fresh water usually holds about one million bacterial
cells.
•The earth is estimated to hold at least 5 nonillion bacteria, and
much of the earth’s biomass is thought to be made up of bacteria.
3. TYPES OF BACTERIA
Bacteria are classified into 7 groups according to their basic shapes
and They can exist as single cells, in pairs, chains or clusters.
1. Cocci (from kokkos meaning berry) are spherical or oval cells.
a) Division in one plane :
• Diplococcus: cocci arranged in pairs
• Streptococcus: cocci arranged in chains
b) Division in two planes :
• Tetrad: cocci arranged in squares of 4
4. TYPES OF BACTERIA
c) Division in three planes :
• Sarcina: cocci in arranged cubes of 8
d) Division in random planes :
• Staphylococcus: cocci arranged in irregular,
often grape-like clusters
An average coccus is about 0.5-1.0 micrometer (µm) in diameter.
(A micrometer equals 1/1,000,000 of a meter.)
5. TYPES OF BACTERIA
2. Bacilli (from bacillus meaning rod) are rod shaped cells.
Bacilli all divide in one plane :
a) Diplobacillus: double bacilli.
b) Streptobacillus: bacilli arranged in
chains.
a) Coccobacillus: oval and similar to a
coccus.
• An average bacillus is 0.5-1.0 µm wide by 1.0-4.0 µm long.
6. TYPES OF BACTERIA
3. Spirals come in one of three forms, a vibrio, a spirillum, or a
spirochete.
a) Vibrios are comma shaped curved rods and
derive their name from their characteristics
vibratory motility.
a) Spirilla are rigid spiral cells.
b) Spirochetes (from speira meaning coil and chaite meaning hair or
a corkscrew ) are flexuous spiral forms.
• Spirals range in size from 1 µm to over 100 µm in length.
8. TYPES OF BACTERIA
4. Actinomycetes (from actis meaning ray
and mykes meaning fungus) are branching
filamentous bacteria, so called because of a
fancied resemblance to the radiating rays of
the sun when seen in tissue lesions.
5. Mycoplasmas are bacteria that are cell
wall deficient and hence do not possess a
stable morphology. They occur as round or
oval bodies and as interlacing filaments.
ACTINOMYCETES
MYCOPLASMAS
10. 1. CELL WALL
•Beneath the external structures is the cell wall. It is very
rigid & gives shape to the cell. Its main function is to
prevent the cell from expanding & eventually bursting
due to water uptake.
•Cell Wall constitutes a significant portion of the dry
weight of the cell and it is essential for bacterial growth
& division. The cell wall cannot be seen by direct light
microscopy and does not stain with simple stains. It may
be demonstrated by micro dissection, reaction with
specific antibodies, mechanical rupture of the cell,
differential staining procedures or by electron
microscopy.
11. 1. CELL WALL
•The cell walls of bacteria usually contain the polysaccharide, peptidoglycan, which
is porous and lets small molecules through.
•Together, the cell membrane and cell wall are referred to as the cell envelope. The
cell wall is an essential part of survival for many bacteria.
•It provides mechanical structure to bacteria, which are single-celled, and it also
protects them from internal turgor pressure.
•Bacteria have higher concentration of molecules such as proteins within themselves
as compared to their environment, so the cell wall stops water from rushing into the
cell.
•Differences in cell wall thickness also make Gram staining possible.
•Gram staining is used for the general identification of bacteria; bacteria with thick
cell walls are gram-positive, while bacteria with thinner cell walls are gram-negative.
12. TYPES OF CELL WALL
On the basis of cell wall composition, bacteria are classified into
two major group i.e.. Gram Positive and Gram negative.
13. TYPES OF CELL
1. Gram positive cell wall :
Cell wall composition of gram positive bacteria.
•Peptidoglycan
•Lipid
•Teichoic acid
2. Gram negative cell wall :
Cell wall composition of gram negative bacteria.
•Peptidoglycan
•Outer membrane:
i. Lipid
ii. Protein
iii. Lipopolysaccharide (LPS)
Characteristics Gram
Positive
Gram
Negative
Thickness Thicker Thinner
Variety of amino acids Few Several
Lipids Present Present
Teichoic acid Present Absent
14. Composition of cell wall
1. Peptidoglycan:
•Peptidoglycan is porous cross linked polymer which is
responsible for strength of cell wall.
•Peptidoglycan is composed of three components.
i. Glycan backbone.
ii. Tetra-peptide side chain (chain of 4 amino acids)
linked to NAM.
iii. Peptide cross linkage.
•Glycan backbone is the repeated unit of N-acetyl
muramic acid (NAM) and N-acetyl glycosamine (NAG)
linked by β-glycosidic bond.
15. •The glycan backbone are cross linked by tetra-peptide
linkage. The tetra-peptide are only found in NAM.
More than 100 peptidoglycan are known with the
diversity focused on the chemistry of peptide
cross linkage and interbridge.
•Although the peptidoglycan chemistry vary from organism
to organism the glycan backbone i.e. NAG-NAM is same in
all species of bacteria.
COMPOSITION OF CELL WALL
16. Peptide cross linkage in Gram positive and Gram negative
bacteria
•The amino acids found in tetra-peptide are-
1. L- alanine : 1st position in both gm+ve and
gm-ve bacteria
2. D- glutamic acid : 2nd position
3. D- aminopimelic acid: 3rd position (variation occurs)
/L-lysine
4. D- alanine : 4th position
•In gram negative bacteria, peptide cross linkage occur
between Diaminopamilic acid (3rd position) of one glycan
back bone and D-alanine of adjacent glycan back bone.
•In gram positive bacteria, peptide cross linkage occur by peptide interbridge.
The type and number of amino acids in interbridge vary among bacterial species.
17. COMPOSITION OF CELL WALL
The functions of Teichoic acid are :
i. gives negative charge
ii. major antigenic determinant
iii. transport ions
iv. Anchoring
v. External permeability barrier
2. Teichoic acid:
•Teichoic acid is water soluble polymer of glycerol or ribitol phosphate.
•It is present in gram positive bacteria.
•It constitutes about 50% of dry weight of cell wall.
•It is the major surface antigen of gram positive bacteria.
18. COMPOSITION OF CELL WALL
•Chemically the cell wall is composed of
peptidoglycan. Mucopeptide
(peptidoglycan or murien) formed by N-
acetyl glucosamine & N-acetyl muramic
acid alternating in chains, cross linked by
peptide chains. Embedded in it are
polyalcohol called Teichoic acids. Some are
linked to Lipids & called Lipoteichoic acid.
Lipotechoic acid link peptidoglycan to
cytoplasmic membrane and the
peptidoglycan gives rigidity.
19. COMPOSITION OF CELL WALL
3. Outer membrane:
•Outer membrane is found only in Gram-negative bacteria, it functions as an initial barrier to
the environment and is composed of lipopolysaccharide
(LPS) and phospholipids
•Function of outer membrane:
i. Structure component of gram-ve cell wall
ii. LPS is an endotoxin produced by gram-ve bacteria
iii. Lipid-A is antigenic
4. LPS:
•LPS is attached to outer membrane by hydrophobic bond. LPS is synthesized in cytoplasmic
membrane and transported to outer membrane.
20. COMPOSITION OF CELL WALL
•LPS is composed of lipid-A and polysaccharide.
•Lipid-A: it is phosphorylated glucosamine disaccharide.
•Polysaccharide: it consists of core-polysaccharide and O-polysaccharide.
•The LPS present on the cell walls of Gram-negative bacteria account for their
endotoxic activity and antigen specificity.
•A bacterium is referred as a protoplast when it is without cell wall. Cell wall may be
lost due to the action of lysozyme enzyme, which destroys peptidoglycan. This cell is
easily lysed and it is metabolically active but unable to reproduce.
•A bacterium with a damaged cell wall is referred as spheroplasts. It is caused by the
action of toxic chemical or an antibiotic, they show a variety of forms and they are able
to change into their normal form when the toxic agent is removed, i.e. when grown on
a culture media.
21. 2. CELL MEMBRANE
•Cytoplasmic membrane is present immediately beneath the cell wall, found in both Gram
positive & negative bacteria and it is a thin layer lining the inner surface of cell wall and
separating it from cytoplasm.
•It acts as a semi permeable membrane controlling the flow of metabolites to and from the
protoplasm.
•The plasma membrane not only defines the borders of the cell, but also allows the cell to
interact with its environment in a controlled way.
•Cells must be able to exclude, take in, and excrete various substances, all in specific amounts.
In addition, they must able to communicate with other cells, identifying themselves and
sharing information.
•To perform these roles, the plasma membrane needs lipids, which make a semi-permeable
barrier between the cell and its environment.
22. 2. CELL MEMBRANE
•It also needs proteins, which are involved in cross-membrane transport and cell
communication, and carbohydrates (sugars and sugar chains), which decorate both the
proteins and lipids and help cells recognize each other.
•Here, we’ll take a closer look at the different components of the plasma membrane,
examining their roles, their diversity, and how they work together to make a flexible, sensitive,
and secure boundary around the cell.
•Cytoplasm
•The cytoplasm is a Colloidal system containing a variety of organic and inorganic solutes
containing 80% Water and 20% Salts, Proteins. They are rich in ribosomes, DNA & fluid. DNA is
circular and haploid. They are highly coiled with intermixed polyamines & support proteins.
Plasmids are extra circular DNA.
23. 2. CELL MEMBRANE
Ribosome
They are the centers of protein synthesis. They are slightly smaller than the ribosome of
eukaryotic cells.
Mesosomes
They are vesicular, convoluted tubules formed by invagination of plasma membrane into the
cytoplasm. They are principal sites of respiratory enzymes and help with cell reproduction.
Cytoplasmic Inclusions
The Inclusion bodies are aggregates of polymers produced when there is excess of nutrients in
the environment and they are the storage reserve for granules, phosphates and other
substances. Volutin granules are polymetaphosphates which are reserves of energy and
phosphate for cell metabolism and they are also known as metachromatic granules.
24. FLUID MOSAIC MODEL
The fluid mosaic model describes the structure of
the plasma membrane as a mosaic of
components —including phospholipids,
cholesterol, proteins, and carbohydrates—that
gives the membrane a fluid character. Plasma
membranes range from 5 to 10 nm in thickness.
The proportions of proteins, lipids, and
carbohydrates in the plasma membrane vary
with cell type. For example, myelin contains 18%
protein and 76% lipid. The mitochondrial inner
membrane contains 76% protein and 24% lipid.
25. FLUID MOSAIC MODEL
1. The main fabric of the membrane is composed of
amphiphilic or dual-loving, phospholipids molecules.
•The hydrophilic or water-loving areas of these molecules are in
contact with the aqueous fluid both inside and outside the cell.
Hydrophobic, or water-hating molecules, tend to be non- polar.
•A phospholipids molecule consists of a three-carbon glycerol
backbone with two fatty acid molecules attached to carbons 1
and 2, and a phosphate-containing group attached to the third
carbon.
•This arrangement gives the overall molecule an area described
as its head (the phosphate-containing group), which has a polar
character or negative charge, and an area called the tail (the
fatty acids), which has no charge.
26. FLUID MOSAIC MODEL
•They interact with other non-polar molecules in
chemical reactions, but generally do not interact with
polar molecules.
•When placed in water, hydrophobic molecules tend to
form a ball or cluster. The hydrophilic regions of the
phospholipids tend to form hydrogen bonds with
water and other polar molecules on both the exterior
and interior of the cell. Thus, the membrane surfaces
that face the interior and exterior of the cell are
hydrophilic.
•In contrast, the middle of the cell membrane is
hydrophobic and will not interact with water.
27. FLUID MOSAIC MODEL
•Therefore, phospholipids form an excellent lipid bilayer cell membrane that separates fluid
within the cell from the fluid outside of the cell.
2. Proteins make up the second major component of plasma membranes. Integral proteins
(some specialized types are called integrins) are integrated completely into the membrane
structure, and their hydrophobic membrane-spanning regions interact with the hydrophobic
region of the phospholipids bilayer.
•Single-pass integral membrane proteins usually have a hydrophobic transmembrane segment
that consists of 20–25 amino acids.
•Some span only part of the membrane—associating with a single layer—while others stretch
from one side of the membrane to the other, and are exposed on either side.
•Some complex proteins are composed of up to 12 segments of a single protein, which are
extensively folded and embedded in the membrane.
28. FLUID MOSAIC MODEL
•This type of protein has a hydrophilic region or regions, and one or several mildly hydrophobic
regions. This arrangement of regions of the protein tends to orient the protein alongside the
phospholipids, with the hydrophobic region of the protein adjacent to the tails of the
phospholipids and the hydrophilic region or regions of the protein protruding from the
membrane and in contact with the cytosol or extracellular fluid.
3. Carbohydrates are the third major component of plasma membranes.
•They are always found on the exterior surface of cells and are bound either to proteins
(forming glycoprotein) or to lipids (forming glycolipids).
•These carbohydrate chains may consist of 2–60 monosaccharide units and can be either
straight or branched.
•Along with peripheral proteins, carbohydrates form specialized sites on the cell surface that
allow cells to recognize each other.
29. FLUID MOSAIC MODEL
•This recognition function is very important to cells, as it allows the immune system to
differentiate between body cells (called “self”) and foreign cells or tissues (called “non-self”).
•Similar types of glycoprotein and glycolipids are found on the surfaces of viruses and may
change frequently, preventing immune cells from recognizing and attacking them.
•These carbohydrates on the exterior surface of the cell—the carbohydrate components of
both glycoprotein and glycolipids—are collectively referred to as the glycocalyx (meaning
“sugar coating”).
•The glycocalyx is highly hydrophilic and attracts large amounts of water to the surface of the
cell. This aids in the interaction of the cell with its watery environment and in the cell’s ability
to obtain substances dissolved in the water.
30. 3. CAPSULE
•Capsule is the outer most layer of the bacteria (extra
cellular). It is a condensed well defined layer closely
surrounding the cell.
•They are usually polysaccharide and if polysaccharide
envelops the whole bacterium it is capsule and their
production depends on growth conditions. They are
secreted by the cell into the external environment and
are highly impermeable.
•When it forms a loose mesh work of fibrils extending
outward from the cell they are described as glycocalyx
and when masses of polymer that formed appear to be
totally detached from the cell and if the cells are seen
entrapped in it are described as slime layer.
31. 3. CAPSULE
•The Capsule protects against
complement and is antiphagocytic.
The Slime layer & glycocalyx helps in
adherence of bacteria either to
themselves forming colonial masses
or to surfaces in their environment
and they resists phagocytosis and
desiccation of bacteria.
32. 4. FLAGELLA
•Flagella are helical structures that bacteria use for
motility. They are very different from eukaryotic
flagella.
•Bacterial flagella are made of millions of subunits of
a single protein (called "flagellin") which self-
assemble to form a long, helical structure outside the
cell.
•The flagellum is anchored into the cell membrane by
a basal body - a complex structure that both holds
the flagellum to the cell and allows it to rotate.
•When energy is used to rotate the basal body
"motor", the flagellum rotates (much like a
corkscrew) and the cell moves forward.
33. 4. FLAGELLA
•Flagella are arranged in many different ways.
•Bacteria can have a single, polar flagellum at
one end of the cell, or can have a tuft of many
flagella at one end.
•Some bacteria even have peritrichous flagella,
scattered all over their cell.
•A very unique groups of bacteria, the
spirochetes, have structures similar to flagella
(called axial filaments) between 2 membranes,
in the periplasmic space.
34. TYPES OF FLAGELLA
There are four different types of flagella:
A. Monotrichous: A single flagellum at one end or the other.
These are known as polar flagellum and can rotate clockwise
and anti-clockwise. The clockwise movement moves the
organism forward while the anti-clockwise movement pulls it
backwards.
B. Peritrichous: Several flagella attached all over the
organism. These are not polar flagella because they are found
all over the organism. These flagella rotate anti-clockwise and
form a bundle that moves the organism in one direction. If
some of the flagella break and start rotating clockwise, the
organism does not move in any direction and begins tumbling.
35. TYPES OF FLAGELLA
C. Lophotrichous: Several flagella at one end of the
organism or the other. These are known as polar
flagellum and can rotate clockwise and anti-
clockwise. The clockwise movement moves the
organism forward while the anti-clockwise
movement pulls it backwards.
D. Amphitrichous: Single flagellum on both the ends
of the organism. These are known as polar
flagellum and can rotate clockwise and anti-
clockwise. The clockwise movement moves the
organism forward while the anti-clockwise
movement pulls it backwards.
36. 5. NUCLEOID
•Inside every living organisms, there is
an area that stores all the genetic
material and controls cellular activities.
In prokaryotes, the same is undertaken
by the NUCLEOID.
•The nucleoid is the space within a
prokaryotic cell where the genetic
information, called the genophore, is
found.
•It attached to the cell membrane and in
immediate contact with the cytoplasm.
37. 5. NUCLEOID
•The nucleoid is mostly composed of multiple compacted copies of DNA in a continuous
thread, with the addition of some RNA and proteins.
•The DNA in prokaryotes is double-stranded and generally takes a circular shape.
38. 6. BACTERIAL SPORE
•Spore is metabolically dormant structure produced during unfavorable condition by the
process called sporulation.
•Sporulation occur during late log phase or early stationary phase.
•Under favorable condition spores germinate to give vegetative cell.
•Size: 0.2 µm.
•Spore are resistant to nutrition starvation, temperature, extreme pH, antibiotics etc.
•Spore formation (sporulation) occurs when nutrients, such as sources of carbon and nitrogen
are depleted. Bacterial spores are highly resistant to
i. Heat
ii. Dehydration
iii. Radiation
iv. Chemicals.
39. 6. BACTERIAL SPORE
•An endospore is structurally and chemically more complex than the vegetative cell. It contains
more layers than vegetative cells.
•Resistance of Bacterial spore may be mediated by dipicolinic acid, a calcium ion chelator
found only in spores.
•When the favorable condition prevail, (i.e. availability of water, appropriate nutrients) spores
germination occurs which forms vegetative cells of pathogenic bacteria.
•Following factors/constituents plays major role for the resistance of Bacterial Spore:
i. Calcium dipicolinate in core
ii. Keratin spore coat
iii. New enzymes (i.e., dipicolinic acid synthetase, heat-resistant catalase)
iv. Increases or decreases in other enzymes.
•A mature endospore contains a complete set of the genetic material (DNA) from the
vegetative cell, ribosome and specialized enzymes.
40. 6. BACTERIAL SPORE
•The shape and the position of spores vary in different species and can be useful for
classification and identification purposes. Endospores may be located in the middle of the
bacterium (central), at the end of the bacterium (terminal) and near the end of the bacteria
(sub terminal) and may be spherical or elliptical.
Types of bacterial spore
1. Endospore:
It is produced within the bacterial cell.
Bacteria producing endospore are: Bacillus,
Clostridium, Sporosarcina etc
2. Exospores:
It is produced outside the cell
Bacteria producing exospores: Methylosinus
Hinweis der Redaktion
FACIED : EASILY SEEN
TISSUE LESION : ANY DAMAGE OR CHANGE IN TISSUE
The fluid mosaic model was first proposed by S.J. Singer and Garth L. Nicolson in 1972 to explain the structure of the plasma membrane. The model has evolved somewhat over time, but it still best accounts for the structure and functions of the plasma membrane as we now understand them.
amphiphilic: Having one surface consisting of hydrophilic amino acids and the opposite surface consisting of hydrophobic (or lipophilic) ones.
hydrophilic: Having an affinity for water; able to absorb, or be wetted by water, “water-loving.”
hydrophobic: Lacking an affinity for water; unable to absorb, or be wetted by water, “water-fearing.”