BACTERIAL MORPHOLOGY and INTERNAL STRUCTURE

1. Microbiology

2. Bacteria
Morphology, Cell structure and Growth

3. BASIC CELL TYPES
● All living cells can be classified as either prokaryotic, from the Greek
words pro (before) and karyon (nucleus), or eukaryotic, from eu (true)
and karyon (nucleus).
Prokaryotic cells
● lack a nucleus and other membrane-enclosed structures,
● All prokaryotes are single-celled organisms, and all are bacteria
whereas eukaryotic cells
● have nucleus and other membrane-enclosed structures
● Eukaryotes include all plants, animals, fungi, and protists
(organisms such as Amoeba, Paramecium, and the malaria
parasite).
Prokaryotic and eukaryotic cells are similar in several ways.
● Both are surrounded by a cell membrane, or plasma membrane.
Although some cells have structures that extend beyond this
membrane or surround it, the membrane defines the boundaries of
the living cell.
● Both prokaryotic and eukaryotic cells also encode genetic
information in DNA molecules.
But these two types of cells are different in other, important ways.

4. PROKARYOTIC CELLS
Detailed studies of cells have revealed that prokaryotes differ
enough to be split into two large groups called domains. A relatively
new concept in biological classification, domain is the highest
category, higher even than kingdom.
Three domains exist: two prokaryotic and one eukaryotic:
● Archaea (archaeobacteria) (from archae, ancient)
● Bacteria
● Eukarya
All members of Archaea and Bacteria are prokaryotes and have
traditionally been called types of bacteria.
Most bacteria on this planet, both in the environment and living in
and on humans, are members of the domain Bacteria. As yet, we
know of no disease-causing Archaea, but they may be involved in
disease of the gums. However, they are very important in the
ecology of our planet, especially in extreme environments, such as
in deep-sea hydrothermal vents, where sulfur-laden water, at
temperatures exceeding the boiling point of water, gushes out from
openings in the ocean floor.

5. SIZE
Prokaryotes are among the smallest of all organisms.
● Most prokaryotes range from 0.5 to 2.0 Micrometer in diameter.
● For comparison, a human red blood cell is about 7.5 Micrometer
in diameter.
Although we often use diameter to specify cell size,
● Many cells are not spherical in shape.
● Some spiral bacteria have a much larger diameter, and
● Some cyanobacteria (formerly called blue-green algae)
are 60 micrometers long. Because of their small size,
bacteria have a large surface-to-volume ratio. For
example, spherical bacteria with a diameter of 2
Micrometer have a surface area of about 12 Micrometer
per square and a volume of about 4 Micrometer per
cube.
The large surface-to-volume ratio of bacteria means that no internal
part of the cell is very far from the surface and that nutrients can
easily and quickly reach all parts of the cell.

6. SHAPE
Typically bacteria come in three basic shapes—spherical, rodlike, and
spiral but variations abound.
● A spherical bacterium is called a coccus (kok`us; plural: cocci
[kok`se]), and
● A rodlike bacterium is called a bacillus (ba-sil`us; plural: bacilli [bas-
il`e]). Some bacteria, called coccobacilli, are short rods
intermediate in shape between cocci and bacilli.
● Spiral bacteria have a variety of curved shapes.
■ A comma-shaped bacterium is called a vibrio (vib`re-o);
■ A rigid, wavy-shaped one, a spirillum(spiril`um; plural:
spirilla); and
■ A corkscrew-shaped one, a spirochete (spi`ro-ket).
Some bacteria do not fit any of the preceding categories but rather have
spindle shapes or irregular, lobed shapes.
● Square bacteria were discovered on the shores of the Red Sea in
1981. They are 2 to 4 micrometer on a side and sometimes
aggregate in wafflelike sheets.
● Triangular bacteria were not discovered until 1986.

7. Even bacteria of the same kind sometimes vary in size and shape.
When nutrients are abundant in the environment and cell division is
rapid, rods are often twice as large as those in an environment with only
a moderate supply of nutrients. Although variations in shape within a
single species of bacteria are generally small, there are exceptions.
● Some bacteria vary widely in form even within a single culture, a
phenomenon known as pleomorphism.
Pleomorphism (from Ancient Greek πλέω-, pléō, "more", and
-μορφή, morphḗ, form) is the ability of some microorganisms
to alter their morphology, biological functions or reproductive
modes in response to environmental conditions.
● Pleomorphism has been observed in some members of the
Deinococcaceae family of bacteria.One factor that affects the
pleomorphism of some bacteria is their nutrition. For example, the
bacterium Deinococcus radiodurans has been shown to exhibit
pleomorphism in relation to differences in the nutrient contents of its
environment.

10. ARRANGEMENT
In addition to characteristic shapes, many bacteria also are found in
distinctive arrangements of groups of cells. Such groups form when
cells divide without separating.
Cocci
Cocci can divide in one or more planes, or randomly.
● Division in one plane produces
■ cells in pairs (indicated by the prefix diplo-) or
■ in chains (strepto-).
● Division in two planes produces
■ cells in tetrads (four cells arranged in a cube).
● Division in three planes produces
■ sarcinae (singular: sarcina; eight cells arranged in a cube)
● Random division planes produce grapelike clusters (staphylo-)
Bacilli
They divide in only one plane, but they can produce
■ cells connected end-to-end (diplo- or streptobacillus)
■ side-by-side (palisade Bascillus)
Spiral bacteria are not generally grouped together.

13. STRUCTURE
Structurally, bacterial cells consist of the following:
1. A cell membrane, usually surrounded by a cell wall and sometimes by an
additional outer layer.
2. An internal cytoplasm with ribosomes, a nuclear region, and in some
cases granules and/or vesicles.
3. A variety of external structures, such as capsules, flagella, and pili.

14. EXTERNAL STRUCTURES

15. 1. Cell wall
2. Flagella
3. Pili
4. Glycocalyx
a. Capsule
b.Slime layer

16. The Cell Wall
The semirigid Cell Wall lies outside the cell membrane in nearly all bacteria.
It performs two important functions.
● First, it maintains the characteristic shape of the cell. If the cell wall is
digested away by enzymes, the cell takes on a spherical shape.
● Second, it prevents the cell from bursting when fluids flow into the cell
by osmosis. Although the cell wall surrounds the cell membrane, in
many cases it is extremely porous and does not play a major role in
regulating the entry of materials into the cell.
COMPONENTS OF CELL WALLS
● Peptidoglycan (peppti-do-gly`-kan), also called murein (from
murus, wall), is the single most important component of the bacterial
cell wall. It is a polymer so large that it can be thought of as one
immense, covalently linked molecule. It forms a supporting net around a
bacterium that resembles multiple layers of chain-link fence.
● In the peptidoglycan polymer, molecules of N-acetylglucosamine
(gluNAc) alternate with molecules of N-acetylmuramic acid (murNAc).
These molecules are cross-linked by tetrapeptides, chains of four
amino acids.

17. ● Amino acids, like many other organic compounds, have
stereoisomers—structures that are mirror images of each other,
just as a left hand is a mirror image of a right hand. Some of the
amino acids in the tetrapeptide chains are mirror images of those
amino acids most commonly found in living things. Those chains are
not readily broken down because most organisms lack enzymes that
can digest the stereoisomeric forms.
PERIPLASMIC SPACE
● Another distinguishing characteristic of many bacteria is the
presence of a gap between the cell membrane and the cell wall. In
these organisms the gap is called the periplasmic(per`e-plazpmik)
space.
● It represents a very active area of cell metabolism. This space
contains not only the cell wall peptidoglycan but also many
digestive enzymes and transport proteins that destroy potentially
harmful substances and transport metabolites into the bacterial
cytoplasm, respectively. The periplasm consists of the
peptidoglycan, protein constituents, and metabolites found in
the periplasmic space.

19. Gram Positive Bacteria
Peptidoglycan
● Gram-positive cells may have as many as 40 such layers of
petidoglycan And form relatively thick layer of peptidoglycan, 20 to
80 nm across.In the peptidoglycan polymer, the third amino acid in
tetrapeptides is lysine. The peptidoglycan layer is closely attached
to the outer surface of the cell membrane. Chemical analysis shows
that 60 to 90% of the cell wall of a Gram positive bacterium is
peptidoglycan. Except for those of streptococci, most Gram-positive
cell walls contain very little protein.
Techoic acid
● Cell walls of Gram-positive organisms have an additional molecule,
teichoic acid. Teichoic (tie-ko`ik) acid,which consists of glycerol,
phosphates, and the sugar alcohol ribitol, occurs in polymers
up to 30 units long. These polymers extend beyond the rest of the
cell wall, even beyond the capsule in encapsulated bacteria.
Although its exact function is unclear, teichoic acid furnishes
attachment sites for bacteriophages and probably serves as a
passageway for movement of ions into and out of the cell.

20. PERIPLASMIC SPACE
● Periplasmic spaces are rarely observed in Gram positive bacteria.
However, such bacteria must accomplish many of the same
metabolic and transport functions that Gram-negative bacteria do. At
present most Gram positive bacteria are thought to have only
periplasms—not periplasmic spaces—where metabolic digestion
occurs and new cell wall peptidoglycan is attached. The periplasm in
Gram-positive cells is thus part of the cell wall.
Gram Staining
● The thick cell walls of Gram-positive bacteria retain such stains as
the crystal violet-iodine dye in the cytoplasm, but yeast cells, many
of which have thick walls but no peptidoglycan, also retain these
stains. Thus, retention of Gram stain seems to be directly related to
wall thickness and not to peptidoglycan. Physiological damage or
aging can make a Gram-positive cell wall leaky, so the dye complex
escapes

22. Gram Negative Bacteria
PEPTIDOGLYCAN
● The cell wall of a Gram negative bacterium is thinner but more complex
than that of a Gram-positive bacterium. Only 10 to 20% of the cell wall is
peptidoglycan; the remainder consists of various polysaccharides,
proteins, and lipids. In most Gram-negative organisms, the third amino acid
is diaminopimelic acid.
OUTER MEMBRANE.
● The outer membrane, found primarily in Gram-negative bacteria, is a bilayer
membrane. It forms the outermost layer of the cell wall and is attached to the
peptidoglycan by an almost continuous layer of small lipoprotein molecules
(proteins combined with a lipid).
● The lipoproteins are embedded in the outer membrane and covalently bonded
to the peptidoglycan. The outer membrane acts as a coarse sieve and exerts
little control over the movement of substances into and out of the cell. However,
it does control the transport of certain proteins from the environment.
● Proteins called porins form channels through the outer membrane.
● Gram-negatives are less sensitive to penicillin than are Gram-positives, in part
because the outer membrane inhibits entrance of penicillin into the cell. The
outer surface of the outer membrane has surface antigens and receptors.
Certain viruses can bind to some receptors as the first step in infecting the

23. LIPOPOLYSACCHARIDE (LPS)
● Also called ENDOTOXIN, is and important part of the outer
membrane and can be used to identify Gram-negative bacteria.
● It is an integral part of the cell wall and is not released until the cell
walls of dead bacteria are broken down.
● LPS consists of polysaccharides and lipid A.
■ The polysaccharides are found in repeating side chains that
extend outward from the organism. It is these repeating units
that are used to identify different Gram-negative bacteria.
■ The lipid A portion is responsible for the toxic properties
that make any Gram-negative infection a potentially serious
medical problem. It causes fever and dilates blood vessels,
so the blood pressure drops precipitously.
● Because bacteria release endotoxin mainly when they are dying,
killing them may increase the concentration of this very toxic
substance. Thus, antibiotics given late in an infection may cause a
worsening of symptoms, or even death of the patient.

24. LPS

25. PERIPLASMIC SPACE
● The gap is most easily observed by electron microscopy of Gram-
negative bacteria. The inner surface of the wall is separated from the
cell membrane by a wider periplasmic space.
● WToxins and enzymes remain in the periplasmic space in sufficient
concentrations to help destroy substances that might harm the
bacterium, but they do not harm the organism that produced them.
Gram Staining
● Gram-negative bacteria fail to retain the crystal violet-iodine dye
during the decolorizing procedure partly because of their thin cell
walls and partly because of the relatively large quantities of
lipoproteins and lipopolysaccharides in the walls.

27. ACID-FAST BACTERIA
● Although the cell wall of acid-fast bacteria, the mycobacteria, is
thick, like that of Gram-positive bacteria, it is approximately 60% lipid
and contains much less peptidoglycan.
● Mycolic acids are long fatty acids found in the cell walls of the
Mycolata taxon, a group of bacteria that includes Mycobacterium
tuberculosis, the causative agent of the disease tuberculosis. They
form the major component of the cell wall of mycolata species.
● Mycolic acid have following general structure
R1CH3 (OH) CH(R2) COOH
● In the acid-fast staining process, carbolfuchsin binds to cytoplasm
and resists removal by an acid-alcohol mixture.
● The lipids make acid-fast organisms impermeable to most other
stains and protect them from acids and alkalis. The organisms grow
slowly because the lipids impede entry of nutrients into cells, and the
cells must expend large quantities of energy to synthesize lipids.
Acid-fast cells can be stained by the Gram stain method; they stain
as Gram-positive.

29. WALL-DEFICIENT ORGANISMS
● Bacteria that belong to the genus Mycoplasma have no cell walls.
● They are protected from osmotic swelling and bursting by a strengthened
cell membrane that contains sterols.
● However, the protection is not complete, and often mycoplasmas must be
grown in special media. Without a rigid cell wall, they vary widely in shape,
often forming slender, branched filaments and exhibiting extreme
pleomorphism.
Other genera of bacteria may normally have a cell wall but can suddenly
lose their ability to form cell walls.
● These wall-deficient strains are called L-forms, named after the Lister
Institute, where they were discovered over 70 years ago. The loss may
occur naturally or be caused by chemical treatment. L-forms may play a
role in chronic or recurrent diseases.
● Treatment with antibiotics that affect cell wall synthesis will kill most of the
bacteria in some infections, but it leaves a few alive as L-forms. When
treatment is discontinued, the L-forms can revert to walled forms and
regrow an infecting population. An example of this is found in the
association of the bacterium Mycobacterium paratuberculosis with Crohn’s
disease, a chronic disorder of the intestine.

30. Archaea
Some Archaea may entirely lack cell walls, while others have unusual
walls of polysaccharides, or of proteins, but lack true peptidoglycan.
Instead they have a similar compound called pseudomurein

32. FLAGELLA
A flagellum (plural: flagella) is a long, thin, whip-like helical
structure that helps some single celled organisms move.
● About half of all known bacteria are motile, or capable of movement.
They often move with speed and apparent purpose, and they usually
move by means of long, thin, helical appendages called flagella
(singular: flagellum).
Flagella based bacterial types:
● Bacteria with a single polar flagellum located at one end, or pole, are
said to be monotrichous (mon-o-trik`-us)
● Bacteria with two flagella, one at each end, are amphitrichous (am-
fe-trik`-us)
● Bacteria with truft of flagella at one or both ends are lophotrichous
(lo-fo-trik`us) and
● Bacteria with flagella all over the surface are peritrichous (pe-ri-
trik`us).
● Bacteria without flagella are atrichous (a-trik`us). Cocci rarely have
flagella.

34. Structure of flagella
Diameter
● The diameter of a prokaryote’s flagellum is about one tenth that of a
eukaryote’s flagellum.
Composition
● It is made of protein subunits called flagellin. Each flagellum is
attached to the cell membrane by a basal region consisting of a
protein other than flagellin.
Basal Region of flagella
● The basal region has a
■ hooklike structure and
■ a complex basal body which consists of a central rod or shaft
surrounded by a set of rings.
Hook
The wider region at the base of the flagellum is called a hook. It is
different in structure than that of the filament. Hook connects
filament to the motor portion of the flagellum called a basal body.

35. Basal body
● The basal body is composed of central rod inserted into series of
rings which is attached to cytoplasmic memvbrane and cell wall.
Rings
● L-ring: it is the outer ring present only in Gram -ve bacteria, it
anchored in lipopolysaccharide layer
● P-ring: it is second ring anchored in peptidoglycan layer of cell wall.
● M-S ring: anchored in cytoplasmic membrane. As the M ring turns,
powered by an influx of protons, the rotary motion is transferred to
the filament which turns to propel the bacterium.
Proteins associated with rings
● Mot protein:There are presence of rings that are surrounded by a
pair of proteins called Mot. These proteins actually drive the flagellar
motor causing rotation of the filament.
● Fli protein:Another set of proteins called Fli proteins function as the
motor switch, reversing the rotation of the flagella in response to
intracellular signals.

37. Flagella of Gram Negative Bacteria
● Gram-negative bacteria have 3 pairs of ring
■ a pair of rings embedded in the cell membrane (M-S RING)
■ another pair of rings associated with the peptidoglycan
(P RING)
■ lipopolysaccharide layers of the cell wall (L RING)
Flagella of Gram Positive Bacteria
● Gram-negative bacteria have 2 pairs of ring
■ a pair of rings embedded in the cell membrane (M-S RING)
■ another pair of rings associated with the peptidoglycan
(P RING)

38. Gram Negative Bacteria

39. Gram Positive Bacteria

40. Pili
● Pili (singular: pilus) are tiny, hollow projections.
● They are used to attach bacteria to surfaces and are not involved in
movement.
● A pilus is composed of subunits of the protein pilin.
● Bacteria can have two kinds of pili
1. Long conjugation pili, or F pili (also called sex pili), and
2. Short attachment pili, or fimbriae (fim`-bre-e; singular:
fimbria).
CONJUGATION PILI.
● Conjugation pili (or sex pili), found only in certain groups of bacteria,
attach two cells and may furnish a pathway for the transfer of the
genetic material DNA. This transfer process is called conjugation.
● Such transfers among bacteria cause problems for humans because
antibiotic resistance can be passed on with the DNA transfer.

41. ATTACHMENT PILI.
● Attachment pili, or fimbriae, help bacteria adhere to surfaces, such as
cell surfaces and the interface of water and air.
● They contribute to the pathogenicity of certain bacteria—their
ability to produce disease—by enhancing colonization (the development
of colonies) on the surfaces of the cells of other organisms.
● For example, some bacteria adhere to red blood cells by attachment pili
and cause the blood cells to clump, a process called hemagglutination.
In certain species of bacteria, some individuals have attachment pili and
others lack them.
● Some aerobic bacteria form a shiny or fuzzy, thin layer at the air-water
interface of a broth culture. This layer, called a pellicle, consists of
many bacteria that adhere to the surface by their attachment pili. Thus,
attachment pili allow the organisms to remain in the broth, from which
they take nutrients, while they congregate near air, where the oxygen
concentration is greatest.
● In 2010, it was discovered that the Pseudomonas bacilli use their
attachment pili to push themselves upright and “walk” around on end,
exploring their environment. They can also use pili to move rapidly over
surfaces when they are horizontal

42. GLYCOCALYX
GLYCOCALYX is the currently accepted term used to refer
to all polysaccharide-containing substances found external
to the cell wall, from the thickest capsules to the thinnest
slime layers. All bacteria have at least a thin slime layer.
CAPSULE
SLIME LAYER

43. CAPSULE
A capsule is a protective structure outside the cell wall of the organism
that secretes it. Only certain bacteria are capable of forming capsules,
and not all members of a species have capsules.
Capsules can serve number of functions, depending upon the bacterial
species:
● Provide protection against temporary drying by binding water
molecules
● Block attachments of bacteriophage
● May be antiphagocytic
● Promote attachments of bacteria to surface
Composition of capsules
Most bacterial capsules are composed of polysaccharides and a few are
polypeptide.
● Homopolysaccharide eg S. mutans capsule is made of glucan (a
disaccharide)
● Heteropolysaccharide eg K. pneumoniae capsule is made of
many sugar precursors
● Polypeptide eg Bascillus anthracis capsule made of glutamic

44. SLIME LAYER
● A slime layer is less tightly bound to the cell wall and is
usually thinner than a capsule. When present, it protects the
cell against drying, helps trap nutrients near the cell, and
sometimes binds cells together.
● Slime layers allow bacteria to adhere to objects in their
environment such as rock surfaces or the root hairs of plants,
so that they can remain near sources of nutrients or oxygen.
● This “biofilm” protects bacteria on the bottom of the layers
from environmental or man-made chemicals.
● Some oral bacteria, for example, adhere by their slime layers
and form dental plaque. The slime layer keeps the bacteria in
close proximity to the tooth surface, where they can cause
dental caries. Plaque is extremely tightly bound to tooth
surfaces. If not removed regularly by brushing, it can be
removed only by a dental professional in a procedure called
scaling.