The document provides an overview of bacterial cells, detailing their structure, classification, and functions. It explains the characteristics of both prokaryotic and eukaryotic cells, and further divides bacteria based on shape, cell wall composition, respiration, and nutrition. It also describes the importance of bacteria in ecosystems and their roles in human health, highlighting both pathogenic and beneficial species.

1. Presented By: Jagruti Marathe
Bacteria

2. All livings things (Single and multicellular) are made of cells that share the same
Common Characteristic.
Characteristics of cell and life
Basic Shape
•Spherical
•Cube
•Cylindrical
Internal content
•Cytoplasm
•Surrounded by a Membrane
DNA Chromosome(s)
•Ribosomes
•Metabolic Capabilities

3. Characteristics of cell and life
Two Basic Cell type
Eukaryotic Cell
•Animal, plants, fungi, and protists
•Contain membrane-bound
organelles that compartmentalize
the cytoplasm and perform specific
functions.
Prokaryotic Cell
Bacteria and Archaea
No nucleus or other membrane-
bound organelles

4. Characteristics of life
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Reproduction and heredity- genome composed of DNA packed in
chromosomes , produce offspring sexually
Growth and Development
Metabolism – Chemical and physical life processes

5. Characteristics of life
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Movement and /or irritability – respond to internal/ external stimuli,
self-propulsion of organisms
Cell support, protection, and storage mechanisms cell walls,
vacuoles, granules, and inclusions
Transport of nutrients and waste

6. They are as unrelated to human beings as living things can be, but bacteria are
essential to human life and life on planet Earth.
Although they are notorious for their role in causing human diseases, from tooth
decay to the Black Plague, there are beneficial species that are essential to good
health.
Bacterial cell

7. Bacteria are unicellular, free-living, microorganisms capable of performing all the
essential functions of life.
They possess both DNA and RNA.
Both are Prokaryotic microorganisms that do not contain chlorophyll.
They occur in water, soil, air, food, and all-natural environments.
They can survive extremes of temperature, PH, Oxygen tension, and atmospheric
pressure.
Bacterial cell

8. Bacteria are very small microorganisms that are visible only under a microscope.
Cocci – 1 μm
Bacilli – 1 to 10 μm
Vibrio’s – 0.5–0.8 μm in width and 2–3 μm in length.
Spirilla – 1.4 to 1.7 μm in diameter and up to 60 μm in length, while
Spirochetes – spirochetes are giants, 0.2-0.3 μm in diameter and 20-30 μm in
length
SIZE OF Bacterial cell
Cocci Bacilli Vibrio's Spirilla Spirochetes

9. Actinomycetes – 1–2 μm diameter
Mycoplasma – Elongated or filamentous forms (up to 100 μm long and about 0.4
μm thick)
SIZE OF Bacterial cell
Actinomycetes Mycoplasmas

10. Classification of Bacteria
Bacteria can be classified into various categories based on their features and
characteristics. The classification of bacteria is mainly based on the following:
 Shape
 Composition of the cell wall
 Mode of respiration
 Mode of nutrition
CLASSIFICATION OF Bacterial
CELL-

11. Classification of bacteria based
on Shape
Type of Classification Examples
Bacillus (Rod-shaped) Escherichia coli (E. coli)
Spirilla or spirochete (Spiral) Spirillum volutans
Coccus (Sphere) Streptococcus pneumoniae
Vibrio (Comma-shaped) Vibrio cholerae

13. Classification of bacteria based
on composition of cell wall
Type of Classification Examples
Peptidoglycan cell wall Gram-positive bacteria
Lipopolysaccharide cell wall Gram-negative bacteria

15. Classification of bacteria based
on mode of respiration
Type of Classification Examples
Anaerobic Bacteria Actinomyces
Aerobic Bacteria Mycobacterium

16. Classification of bacteria based
on mode of nutrition
Type of Classification Examples
Autotrophic Bacteria Cyanobacteria
Heterotrophic Bacteria All disease-causing bacteria

17. ● In bacteria, the cell wall forms a rigid
structure of uniform thickness around the
cell and is responsible for the characteristic
shape of the cell (rod, coccus, or spiral).
Structure of bacterial cell

18. ● Bacteria are single-celled, or simple,
organisms that are invisible to the naked
eye. Many bacteria are found both inside and
outside of organisms, including humans.
Bacteria are also found on surfaces and in
substances like water, soil, and food, making
them key players in the Earth's ecosystems.
Structure of bacterial cell

19. ● Internal Structure
In bacteria, the cell wall forms a rigid structure of
uniform thickness around the cell and is
responsible for the characteristic shape of the cell
(rod, coccus, or spiral). Inside the cell wall (or rigid
peptidoglycan layer) is the plasma (cytoplasmic)
membrane; this is usually closely opposed to the
wall layer.
Structure of bacterial cell

20. ● All bacteria, both pathogenic and saprophytic, are
unicellular organisms that reproduce by binary
fission. Most bacteria are capable of independent
metabolic existence and growth, but species
of Chlamydia and Rickettsia are obligately
intracellular organisms.
Structure of bacterial cell

21. • Bacterial cells are extremely small and are most
conveniently measured in microns (10-6 m).
• They range in size from large cells such as Bacillus
anthracis (1.0 to 1.3 µm X 3 to 10 µm) to very small
cells such as Pasteurella tularensis (0.2 X 0.2 to 0.7
µm) Mycoplasmas (atypical pneumonia group) are
even smaller, measuring 0.1 to 0.2 µm in diameter.
• Bacteria, therefore, have a surface-to-volume ratio
that is very high: about 100,000.
Structure of bacterial cell

22. External Structure
Structure of bacterial cell
Appendages
Motility – Flagella and axial filaments
Attachment or Channels- fimbriae and pili
Glycocalyx- Surface coating

23. ● Two types of surface appendage can be recognized
on certain bacterial species: the flagella, which are
organs of locomotion, and pili (Latin hairs), which are
also known as fimbriae (Latin fringes).
● Flagella occur on both Gram-positive and Gram-
negative bacteria, and their presence can be useful
in identification.
Structure of bacterial cell

24. ● For example, they are found on many species of
bacilli but rarely on cocci.
● In contrast, pili occur almost exclusively on Gram-
negative bacteria and are found on only a few
Gram-positive organisms (e.g., Corynebacterium
renale).
● Some bacteria have both flagella and pili.
● e.g.: Escherichia coli.
Structure of bacterial cell

25. ● Bacterial Flagella
Bacterial flagella are long, thin (about 20 nm), 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 that increase their diameter.
Flagella can be seen easily with the electron microscope.
Structure of bacterial cell

26. Flagella
Structurally, bacterial flagella are long (3 to 12 µm),
filamentous surface appendages about 12 to 30 nm in
diameter.
The protein subunits of a flagellum are assembled to
form a cylindrical structure with a hollow core.
Structure of bacterial cell

27. A flagellum consists of three parts:
(1) The long filament, which lies external to the cell
surface;
(2) The hook structure at the end of the filament; and
(3) The basal body, to which the hook is anchored and
which imparts motion to the flagellum. The basal
body traverses the outer wall and membrane
structures.
Structure of bacterial cell

28. ● Basal Body
● It is attached to the cell membrane and
cytoplasmic membrane.
● It consists of rings surrounded by a pair of proteins
called Mot .
● The rings include:
● L-ring: Outer ring anchored in the
lipopolysaccharide layer and found in gram +ve
bacteria.
● P-ring: Anchored in the peptidoglycan layer.
● C-ring: Anchored in the cytoplasm
● M-S ring: Anchored in the cytoplasmic membrane
Structure of bacterial cell

29. ● Basal Body
● It is attached to the cell membrane and
cytoplasmic membrane.
● It consists of rings surrounded by a pair of proteins
called Mot .
● The rings include:
● L-ring: Outer ring anchored in the
lipopolysaccharide layer and found in gram +ve
bacteria.
● P-ring: Anchored in the peptidoglycan layer.
● C-ring: Anchored in the cytoplasm
● M-S ring: Anchored in the cytoplasmic membrane
Structure of bacterial cell

30. ● Hook
● It is a broader area present at the base of the
filament.
● Connects filament to the motor protein in the base.
● The hook length is greater in gram +ve bacteria.
● Filament
● Thin hair-like structure arising from the hook.
Structure of bacterial cell

32. Arrangement and Types
Flagella are attached to cells in different places. As the number and location of flagella are
distinctive for each genus, they can be used in the classification of bacteria. There are four types
of flagellar arrangement.
1.Monotrichous (Mono means one): Single polar flagellum e.g. Vibrio cholerae, Campylobacter
spp. (polar flagella often in pairs to give a “seagull” appearance).
2.Amphitrichous: Single flagellum at both ends e.g. Alcaligenes faecalis (note: amphibians live
both on land and in water).
3.Lophotrichous: Tuft of flagella at one or both ends e.g. Spirilla spp
4.Peritrichous (flagella in the periphery): Flagella surrounding the bacterial cell. All the
members of the family Enterobacteriaceae, if motile have peritrichous flagella.
e.g. Salmonella Typhi, Escherichia coli, Proteus spp (highly motile organism; shows swarming
motility)

34. Functions of Bacterial Flagella
•Organs of locomotion: Many prokaryotes are motile, and the majority of motile prokaryotes
move by means of flagella.
•Role in Pathogenesis: Escherichia coli and Proteus spp are common causes of urinary tract
infections. The flagella of these bacteria help the bacteria by propelling the bacteria from the
urethra into the bladder.
•Roles in Organism identification
• Some species of bacteria, e.g. Salmonella species are identified in the clinical
laboratory by the use of specific antibodies against flagellar proteins.
• Organisms such as Vibrio cholerae (darting motility) and Proteus species (swarming
growth in common culture media) are easily identified by their characteristics motility
pattern.

35. Properties Bacterial flagella Archeal flagella
Flagellar filament
Flagellar filament is made
up of a single type of
protein
Several different flagellin
proteins are found.
Diameter of Flagella
The diameter of bacterial
flagella is 15-20 nm
depending on the species.
Archaeal flagella is roughly
half the diameter of
bacterial flagella, measuring
only 10–13 nm in width.
Source of energy for the
rotation of flagella
Proton motive force ATP

36. ● Fimbriae and Pili
Fimbriae and pili, both are appendages on the cell wall
of the bacteria.
These thin protein tubes originate from the cytoplasmic
membrane of several bacteria, protruding out after it
penetrates the peptidoglycan layer of the cell wall.
While the fimbriae are bristle-like short fibers occurring
on the bacterial surface, Pili are long hair-like tubular
microfibers found on the surface of bacteria.
Structure of bacterial cell

37. ● The pili are found in some gram-negative bacteria only,
whereas the fimbriae are found in both the gram-negative and
gram-positive bacteria.
● Both fimbriae and pili are capable of sticking to the bacterial
surface. Pili are usually longer and less in number compared
to the fimbriae.
● Virtually, they are found in all gram-negative bacteria but not
as much in gram-positive bacteria.
Structure of bacterial cell

38. Pilli
Pili are hair –like microfibrils, 0.5-2 µm in length and 5 to
7 nm in diameter.
They are thinner, shorter and more numerous than
flagella.
They are present only on gram -ve bacteria.
It composed of Protein known as pillin and its molecular
weight is 18,000 daltons.
Structure of bacterial cell

39. Pili or fimbriae are unrelated to motility and are found on
motile as well as non-motile cells.
Fimbriae and pili, these two terms are used
interchangeably but they can be distinguished.
Fimbriae can evenly distributed over the entire surface of
the cell or they occur at poles of the bacterial cell . (100
to 200)
Pili are usually longer than fimbriae and only 1 or 2 per
cell.
They join the bacterial cell for transfer the genetic
material(DNA)- (Bacterial conjugation) from one cell to
another cell.
Structure of bacterial cell

40. Pili are of two types –
the long conjugation pili and
the short attachment pili.
The F or sex pili (Long conjugation pili) are long and a
few in number.
This conjugation pilus facilitates conjugation.
Genetic recombination is enabled in gram-negative
bacteria through the transfer of DNA from the male
bacterium to a female bacterium.
Structure of bacterial cell

41. A few names are given to different types of pili by their
function.
The classification does not always overlap with the
structural or evolutionary-based types, as convergent
evolution occurs.
Structure of bacterial cell

42. Fimbriae and Pili – Structure
• Pili and flagella are different in being thinner and shorter, less rigid and straight, and large
in number.
• Their occurrence is either at the poles of a bacterial cell or is evenly distributed over the
cell’s enteric surface.
• The pili have a diameter of close to 250 Å and lengthwise they are 0.2-20 µm.
• Plasmids genetically govern Pili and vary in number, ranging between 1 and 10. The
molecular weight of Fibrillin is close to 16,000 Daltons.
• The Long conjugation pili are helical tubes having a hollow core.
• These structures are the cylinder of repeating protein units.
• The filamentous structure of these is administered by the plasmid of the bacterium.
• The diameter of the Long conjugation pili is 65-135 Å and close to 20 µm lengthwise,
which is greater in comparison to fimbriae.

43. Fimbriae and Pili – Function
• The role of fimbriae and pili is not limited, they are involved in many activities. The
Fimbriate bacteria are the bacterium having fimbriae.
• These fimbriae are adhesive in nature attaching the entity to the substrate that
naturally occurs or to any other entity. Additionally, the fimbriae cause agglutination of
the blood cells such as leukocytes, epithelial cells, erythrocytes, etc.
• The fimbriae are armed with antigenic traits as they serve as thermolabile nonspecific
agglutinogen.
• The fimbriae affect the metabolic processes.
• The cells that contain fimbriae are referred to as Fim cells.
• They have a high rate of metabolic action compared to the cells which do not contain
fimbriae (Fim– cells).
• They operate as aggregation organelles, forming stellate aggregation on a static liquid
medium.
• These pili connect two cells due to their hollow cores serving as conjugation tubes.
• The female cell is identified by the tip of the pilus from where the genetic content of the
donor cell transfers to the female cell.

46. Capsule
Many prokaryotic microorganisms synthesize amorphous
organic exopolymers which are deposited outside the
cell wall called capsules or slime layers or glycocalyx
coats.
The term capsule refers to the layer tightly attached to
the cell wall while the slime layer is the loose structure
that often diffuses into the growth medium.
Structure of bacterial cell

47. The capsule layer may be thin of a size less than 0.2 µm
called a microcapsule and the thick layer of size more
than 0.2 µm to 10 µm called a microcapsule.
Structure of bacterial cell

48. Composition of the capsule:
Complex polysaccharide (Klebsiella pneumoniae)
Or Polypeptide (Bacillus anthracis)
Or Hyaluronic acid (Streptococcus pyogenes).
Water(98%)
Structure of bacterial cell

49. The capsule or slime layer has less affinity for basic dyes
and is not visible in Gram staining.
Special capsule staining techniques are used by using
copper salts as mordants.
Structure of bacterial cell

50. Capsules may be easily observed by negative staining in
wet films with Indian ink. They are seen as clear halos
around the bacteria against a black background.
Capsular material is antigenic and may be demonstrated
by the serological method.
It is visualized by the reaction with a specific antibody
which causes a characteristic swelling of the capsule.
It is known as a quelluing reaction.
Structure of bacterial cell

51. The function of Capsule:
● Capsules protect the bacteria from antibacterial agents such as lytic enzymes.
● They inhibit phagocytosis and contribute to the virulence of pathogenic bacteria.
● They may provide protection against temporary drying by binding water molecules.
● They may block the attachment of bacteriophages.
● They may promote the stability of bacterial suspension by preventing the cells from
aggregation and settling.
● They may promote the attachment of bacteria to surfaces.
Structure of bacterial cell

52. ● Cell wall:
A cell wall is a rigid structure that gives a definite shape
to the cell, situated between the capsule and cytoplasmic
membrane.
It is about 10-20 nm in thickness and constitutes
Structure of bacterial cell

53. It is important to note that not all bacteria have a cell wall. Having said that though, it is
also important to note that most bacteria (about 90%) have a cell wall and they typically
have one of two types:
a gram positive cell wall or a gram negative cell wall.
Structure of bacterial cell

54. ● The two different cell wall types can be identified in the lab by a differential stain
known as the Gram stain.
● Developed in 1884, it’s been in use ever since.
● Originally, it was not known why the Gram stain allowed for such reliable separation
of bacterial into two groups.
● Once the electron microscope was invented in the 1940s, it was found that the
staining difference correlated with differences in the cell walls.
Structure of bacterial cell

55. ● After this stain technique is applied the gram positive bacteria will stain purple, while
the gram negative bacteria will stain pink.
Structure of bacterial cell

56. Gram Stain Process
Gram staining steps Cell effects Gram-positive Gram -negative
Step 1
Crystal violet Primary stain
added to specimen smear.
Stain cells purple or blue Purple or blue purple or blue
Step 2
Iodine
Mordant makes dye less
soluble so it adheres to cell
walls.
Cells remain purple or blue purple or blue purple or blue
Step 3
Alcohol
Decolorize washes away
stain from gram-negative
cell walls .
Gram –Positive cells remain purple or blue.
Gram-negative cells are colorless.
Purple or blue Colorless
Step 4
Safranin
Counterstain allows dye
adherence to gram-
negative cells.
Gram –Positive cells remain purple or blue.
Gram-negative cells appear pink or red.
Purple or blue Pink or red

57. • A cell wall, not just of bacteria but for all organisms, is found outside of the cell membrane.
• It’s an additional layer that typically provides some strength that the cell membrane lacks,
by having a semi-rigid structure.
• Both gram positive and gram negative cell walls contain an ingredient known
as peptidoglycan (also known as murein).
• This particular substance hasn’t been found anywhere else on Earth, other than the cell
walls of bacteria. But both bacterial cell wall types contain additional ingredients as well,
making the bacterial cell wall a complex structure overall, particularly when compared with
the cell walls of eukaryotic microbes.
• The cell walls of eukaryotic microbes are typically composed of a single ingredient, like the
cellulose found in algal cell walls or the chitin in fungal cell walls.

58. • The bacterial cell wall performs several functions as well, in addition to providing overall
strength to the cell.
• It also helps maintain the cell shape, which is important for how the cell will grow,
reproduce, obtain nutrients, and move.
• It protects the cell from osmotic lysis, as the cell moves from one environment to another
or transports in nutrients from its surroundings.
• Since water can freely move across both the cell membrane and the cell wall, the cell is at
risk for an osmotic imbalance, which could put pressure on the relatively weak plasma
membrane.
• Studies have actually shown that the internal pressure of a cell is similar to the pressure
found inside a fully inflated car tire.
• That is a lot of pressure for the plasma membrane to withstand! The cell wall can keep out
certain molecules, such as toxins, particularly for gram negative bacteria.
• And lastly, the bacterial cell wall can contribute to the pathogenicity or disease –causing
ability of the cell for certain bacterial pathogens.

59. • Structure of Peptidoglycan
• peptidoglycan, since it is an ingredient that both bacterial cell walls have in common.
• Peptidoglycan is a polysaccharide made of two glucose derivatives,
• N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM), alternated in long
chains.
• The chains are cross-linked to one another by a tetrapeptide that extends off the NAM
sugar unit, allowing a lattice-like structure to form.

60. • The four amino acids that compose the tetrapeptide are: L-alanine, D-glutamine, L-lysine
or meso-diaminopimelic acid (DPA), and D-alanine.
• Typically only the L-isomeric form of amino acids are utilized by cells but the use of the
mirror image D-amino acids provides protection from proteases that might compromise the
integrity of the cell wall by attacking the peptidoglycan.
• The tetrapeptides can be directly cross-linked to one another, with the D-alanine on one
tetrapeptide binding to the L-lysine/ DPA on another tetrapeptide.
• In many gram positive bacteria there is a cross-bridge of five amino acids such as glycine
(peptide interbridge) that serves to connect one tetrapeptide to another.
• In either case the cross-linking serves to increase the strength of the overall structure, with
more strength derived from complete cross-linking, where every tetrapeptide is bound in
some way to a tetrapeptide on another NAG-NAM chain.

62. Gram Positive Cell walls
• The cell walls of gram positive bacteria are composed
predominantly of peptidoglycan.
• In fact, peptidoglycan can represent up to 90% of the cell
wall, with layer after layer forming around the cell membrane.
• The NAM tetrapeptides are typically cross-linked with a
peptide interbridge and complete cross-linking is common.
• All of this combines together to create an extremely strong
cell wall.

63. • The additional component in a gram-positive cell wall
is teichoic acid, a glycopolymer, which is embedded within
the peptidoglycan layers.
• Teichoic acid is believed to play several important roles for
the cell, such as the generation of the net negative charge of
the cell, which is essential for development of a proton motive
force.
• Teichoic acid contributes to the overall rigidity of the cell wall,
which is important for the maintenance of the cell shape,
particularly in rod-shaped organisms.

64. • There is also evidence that teichoic acids participate in cell
division, by interacting with the peptidoglycan biosynthesis
machinery.
• Lastly, teichoic acids appear to play a role in resistance to
adverse conditions such as high temperatures and high salt
concentrations, as well as to β-lactam antibiotics.
• Teichoic acids can either be covalently linked to
peptidoglycan (wall teichoic acids or WTA) or connected to
the cell membrane via a lipid anchor, in which case it is
referred to as lipoteichoic acid.

65. Since peptidoglycan is relatively porous, most substances can pass through the gram
positive cell wall with little difficulty.
But some nutrients are too large, requiring the cell to rely on the use of exoenzymes.
These extracellular enzymes are made within the cell’s cytoplasm and then secreted past
the cell membrane, through the cell wall, where they function outside of the cell to break
down large macromolecules into smaller components.

66. Gram Negative Cell Walls
The cell walls of gram negative bacteria are more complex than
that of gram positive bacteria, with more ingredients overall.
They do contain peptidoglycan as well, although only a couple
of layers, represent 5-10% of the total cell wall.
What is most notable about the gram-negative cell wall is the
presence of a plasma membrane located outside of the
peptidoglycan layers, known as the outer membrane.
This makes up the bulk of the gram negative cell wall.
The outer membrane is composed of a lipid bilayer, very similar
in composition to the cell membrane with polar heads, fatty acid
tails, and integral proteins.

67. It differs from the cell membrane by the presence of large
molecules known as lipopolysaccharide (LPS), which
are anchored into the outer membrane and project from the cell
into the environment.
LPS is made up of three different components:
1) the O-antigen or O-polysaccharide, which represents the
outermost part of the structure ,
2) the core polysaccharide, and
3) lipid A, which anchors the LPS into the outer membrane.

68. LPS is known to serve many different functions for the cell,
such as contributing to the net negative charge for the cell,
helping to stabilize the outer membrane, and providing
protection from certain chemical substances by physically
blocking access to other parts of the cell wall. In addition, LPS
plays a role in the host response to pathogenic gram negative
bacteria. The O-antigen triggers an immune response in an
infected host, causing the generation of antibodies specific to
that part of LPS (think of E. coli O157). Lipid A acts as a toxin,
specifically an endotoxin, causing general symptoms of illness
such as fever and diarrhea. A large amount of lipid A released
into the bloodstream can trigger endotoxic shock, a body-wide
inflammatory response which can be life-threatening.

69. the gram negative bacteria utilize periplasmic enzymes that are stored in the periplasm.
Where is the periplasm, you ask? It is the space located between the outer surface of the
cell membrane and the inner surface of the outer membrane, and it contains the gram
negative peptidoglycan. Once the periplasmic enzymes have broken nutrients down to
smaller molecules that can get past the LPS, they still need to be transported across the
outer membrane, specifically the lipid bilayer. Gram negative cells utilize porins, which are
transmembrane proteins composed of a trimer of three subunits, which form a pore across
the membrane. Some porins are non-specific and transport any molecule that fits, while
some porins are specific and only transport substances that they recognize by use of a
binding site. Once across the outer membrane and in the periplasm, molecules work their
way through the porous peptidoglycan layers before being transported by integral proteins
across the cell membrane.
.

70. The peptidoglycan layers are linked to the outer membrane by the use of a lipoprotein
known as Braun’s lipoprotein (good ol’ Dr. Braun). At one end the lipoprotein is covalently
bound to the peptidoglycan while the other end is embedded into the outer membrane via its
polar head. This linkage between the two layers provides additional structural integrity and
strength.

72. Bacterial spores are highly resistant, dormant structures (i.e. no metabolic
activity) formed in response to adverse environmental conditions.
When vegetative cells of certain bacteria such as Bacillus spp
and Clostridium spp are subjected to environmental stresses such as nutrient
deprivation, they produce metabolically inactive or dormant form-endospore.
The formation of endospores circumvents the problems associated with
environmental stress and ensures the survival of the organisms.
During unfavourable conditions (especially when carbon and nitrogen
become unavailable) spore-forming bacilli form endospores. The size, shape,
and location of endospores are particularly useful for identifying Clostridium,
Bacillus, and related species.
Bacterial Spores: Structure and Spore-Forming Bacteria

73. Sporulation
Spore formation
(sporulation) occurs when nutrients, such
as sources of carbon and nitrogen are
depleted. Bacterial spores are highly
resistant to
•Heat
•Dehydration
•Radiation and
•Chemicals

75. Structure of the Bacterial Spore
An endospore is structurally and chemically more complex than
the vegetative cell. It contains more layers than vegetative cells.
Resistance of Bacterial spores may be mediated by dipicolinic
acid, a calcium ion chelator found only in spores. When the
favorable condition prevails, (i.e. availability of water, appropriate
nutrients) spores germination occurs which forms vegetative
cells of pathogenic bacteria.
The following factors/constituents play major roles in the
resistance of bacterial spore:
•Calcium dipicolinate in core
•Keratin spore coat
•New enzymes (i.e., dipicolinic acid synthetase, heat-resistant
catalase)
•Increases or decreases in other enzymes.

76. A mature endospore contains a complete set of genetic material (DNA) from the
vegetative cell, ribosomes, and specialized enzymes.
Mature endospores are released from the vegetative cell to become free
endospores.
When the free endospores are placed in an environment that supports growth, the
endospores will revert back to a vegetative cells in a process called germination.
It should be noted that unlike the process of binary fission observed with vegetative
cells, endospore formation is not a reproductive process but a process
of differentiation that provides the bacteria with a mechanism for survival.

77. Constituents of Bacterial Spores
1.Thick keratin-like coat
2.Peptidoglycan
3.Cell membrane
4.A small amount of cytoplasm
5.Very little water
6.Bacterial DNA

78. Medical Importance of Bacterial Spores
Important features of Spores Medical Implications
Spores are highly resistant to heating;
spores are not killed by boiling (100°C) but
are killed at 121°C.
Medical supplies must be heated to 121°C for
at least 15 minutes to be sterilized.
Spores are highly resistant to many
chemicals, including most disinfectants.
The only solution designated as sporicidal will
kill spores.
Spores can survive for many years in soil
and other inanimate objects.
Wounds contaminated with soils can be
infected with spores and cause diseases such
as tetanus, and gas gangrene.
Spores do not exhibit measurable metabolic
activity.
Antibiotics are ineffective against spores.
Spores are formed only when nutrients are
insufficient.
Spores are not often found at the site of
infection because nutrients are not limited.

79. Positions of Bacterial Spores
• The shape and the position of spores vary in different species and
can be useful for classification and identification purposes.
• The position of the spores can be seen in the smear by using the
endospore staining method.
• Endospores may be located in the middle of the bacterium
(central), at the end of the bacterium (terminal), near the end of
the bacteria (subterminal), and maybe spherical or elliptical
1.Central endospores are located within the middle of the vegetative
cell.
2.Terminal endospores are located at the end of the vegetative
cell.
3.Sub-terminal endospores are located between the middle and the
end of the cell

80. Examples
1.Central or equatorial, giving the bacillus a spindle shape (eg. Clostridium bifermentans)
2.Sub-terminal, the bacillus appearing Club shaped (eg. Clostridium perfringens)
3.Oval and terminal, resembling a tennis racket (eg. Clostridium tertium)
4.Spherical and terminal, giving a drumstick appearance (Clostridium tetani)

81. Useful Bacteria
Not all bacteria are harmful to humans. There are some bacteria that are beneficial
in different ways. Listed below are a few benefits of bacteria:
 Convert milk into curd – Lactobacillus or lactic acid bacteria
 Ferment food products – Streptococcus and Bacillus
 Help in digestion and improving the body’s immunity system – Actinobacteria,
Bacteroidetes, Firmicutes, Proteobacteria
 Production of antibiotics, which is used in the treatment and prevention of
bacterial infections – Soil bacteria

82. Harmful Bacteria
There are bacteria that can cause a multitude of illnesses.
They are responsible for many infectious diseases like pneumonia, tuberculosis, diphtheria,
syphilis, and tooth decay.
Their effects can be rectified by taking antibiotics and prescribed medication.
However, precaution is much more effective. Most of these disease-causing bacteria can be
eliminated by sterilizing or disinfecting exposed surfaces, instruments, tools, and other utilities.
These methods include- the application of heat, disinfectants, UV radiations, pasteurization,
boiling, etc.

83. Thankyou