bacterial cell morphology

1. COURSE: AMBE-101
COURSE TITLE: AGRICULTURAL MICROBIOLOGY
CREDITS: 2(1+1)
Review of Bacterial cell structure

2. Cells are basically of two types
Prokaryotic cells and Eukaryotic cells
Prokaryotic cells are primitive type of cells
• Lack true nucleus and other cell organelle (mitochondria, chloroplasts,
endoplasmic reticulum, golgi complex, etc.)
• The word prokaryotes is derived from Greek word (pro=before, karyo=nucleus)
Eukaryotic cells have true nucleus and it also contains cell organelles
• The word eukaryotes is derived from Greek word eu means true and karyo
means nucleus

3. Prokaryotic cells:
• Lacks a defined nucleus hence hereditary material not enclosed in an
envelope has a relatively simple internal organization
• As cell divide by fission and do not contain numerous chromosomes, no
complex cell division machinery has evolved
• consist of a single closed compartment that is surrounded by the plasma
membrane- it is selectively permeable with in pockets (mesosomes)
• Outside the membrane, a rough cell wall rich in carbohydrates and
aminoacids may be present

4. • Eukaryotic cells, unlike prokaryotic cells, contain a defined
membrane-bound nucleus and extensive internal membranes that
enclose other compartments, the organelles
• The region of the cell lying between the plasma membrane and the
nucleus is the cytoplasm, comprising the cytosol (aqueous phase) and
the organelles.
• Eukaryotes comprise all members of the plant and animal
kingdoms, including the fungi, which exist in both multicellular
forms (molds) and unicellular forms (yeasts), and the protozoans
(proto,primitive; zoan, animal), which are exclusively unicellular.

7. Prokaryotic cell Eukaryotic cell
1 A true nucleus is absent A true nucleus is present
2 Nuclear membrane is absent Nuclear membrane is present.
3 Nucleolus is absent Nucleolus is present.
4 Chromosome is single, circular. Chromosomes are many and linear
5 Chromosome present freely in the
cytoplasm
Chromosomes are enclosed inside the nuclear
membrane
6 Histone proteins are absent in the
organisation of chromosome
Chromosomes are well organised with histone
protein
7 In photosynthetic cells, chlorophyll
pigments are present in cell membrane
In photosynthetic cells, the chlorophyll
pigments are present in the plastids of
Chloroplast
8 The cell wall contains amino sugars &
muramic acid
When cell wall present, it does not contain
amino sugars & muramic acid

8. Prokaryotic cell Eukaryotic cell
9 Ribosomes are 70s type Ribosomes are 80s type
10 Cell organells are absent. Cell organells are present
11 Enzymes necessary for respiration are present
in plasmamembrane
Enzymes necessary for respiration are present in
mitochondria
12 Cell division by the process of amitosis i.e.,
mitosis and meiosis is absent
Cell division by the process of mitosis
and meiosis
13 mRNA will not have the 5' methyl cap and 3'
poly A tail.
mRNA having 5' methyl cap and 3‘poly A tail
14 Transcription and translation are combined
process, both takes place in cytoplasm
Transcription and translation are not combined
process. Transcription takes in nucleus, while
translation in cytoplasm
15 In genes non-coding regions are absent In genes non-coding region (i.e., introns) are
present.

10.  0.5 to 1.0 μm in diameter, surface area/ volume ratio is exceedingly high
favoring unusually high rate of growth and metabolism of bacteria.
 No circulatory mechanism is needed to distribute the nutrients that are taken in,
due to this high surface to volume ratio.

11.  The average diameter of spherical bacteria is 0.5-2.0 µm.
 For rod-shaped or filamentous bacteria, length is 1-10 µm and diameter is 0.25-1.0
µm.
 E. coli , a bacillus of about average size is 1.1 to 1.5 µm wide by 2.0 to 6.0 µm long.
 Spirochaetes occasionally reach 500 µm in length and the cyanobacterium
 Oscillatoria is about 7 µm in diameter.
 The bacterium, Epulosiscium fishelsoni , can be seen with the naked eye (600 µm
long by 80 µm in diameter).

13.  One group of bacteria, called the Mycoplasmas, have individuals with size much
smaller than these dimensions. They measure about 0.25 µ and are the smallest cells
known so far. They were formerly known as Pleuro Pneumonia Like Organisms
(PPLO).
 Mycoplasma gallicepticum, with a size of approximately 200 to 300 nm are thought to
be the world smallest bacteria.
 Thiomargarita namibiensis is world’s largest bacteria, a gram-negative Proteobacterium
found in the ocean sediments off the coast of Namibia. Usually it is 0.1—0.3 mm
(100—300 µm) across, but bigger cells have been observed up to 0.75 mm (750 µm).

15.  Structure of bacteria has two aspects, arrangement and shape.
 Due to the presence of a rigid cell wall, bacteria maintain a definite shape, though they vary
as shape, size and structure.
 When viewed under light microscope, most bacteria appear in variations of three major
shapes: the rod (bacillus), the sphere (coccus) and the spiral type (vibrio).
 So far as the arrangement is concerned, it may Paired (diplo), Grape-like clusters (staphylo)
or Chains (strepto).

16. •Cocci (or coccus for a single cell) are round cells, sometimes
slightly flattened when they are adjacent to one another.
•Bacilli (or bacillus for a single cell) are rod-shaped bacteria.
•Spirilla (or spirillum for a single cell) are curved bacteria
which can range from a gently curved shape to a corkscrew-
like spiral. Many spirilla are rigid and capable of movement. A
special group of spirilla known as spirochetes are long,
slender, and flexible.

25. EXTRACELLULAR
STRUCTURES
INTRACELLULAR
STRUCTURES

26. GLYCOCALYX
FLAGELLA
PILI
SHEATH
CELLWALL

27.  Glycocalyx, literally meaning "sugar coat" (glykys = sweet, kalyx = husk), is a
network of polysaccharides that project from cellular surfaces of bacteria,
which classifies it as a universal surface component of a bacterial cell, found
just outside the bacterial cell wall.
 A distinct, gelatinous glycocalyx is called a capsule, whereas an irregular,
diffuse layer is called a slime layer.
This coat is extremely hydrated and stains with ruthenium red.
Many bacterial cells secreted at the time of their active growth.

28.  When the glycocalyx forms a well-defined persistent
layer, it is called capsule.
 The capsule is a major virulence factor in the major
disease-causing bacteria, such as Escherichia
coli and Streptococcus pneumoniae.

29. The functions of the capsule depend on bacterial species
(1) they may block attachment of bacteriophages
(2) they may be antiphagocytic
(3) they may provide protection against temporary drying by
binding water molecules
(4) they may promote attachment of bacteria to surfaces.

30. When the glycocalyx does not form a persistent layer, but is
present more diffusely forming a loose mass around the
bacterial cell, it is called slime layer.
It is easily deformed, difficult to see, and can be very easily
removed by washing the bacterial cells
Gliding bacteria often produce slime, which aids in their
mobility.
It helps bacteria to attach them to the substratum and
lubricates the surface for more efficient movement.

31.  Flagella (singular, flagellum) are hairlike structures that
provide a means of locomotion for those bacteria that have
them.
 They can be found at either or both ends of a bacterium or all
over its surface.
 The flagella beat in a propeller-like motion to help the
bacterium move toward nutrients; away from toxic
chemicals; or, in the case of the photosynthetic
cyanobacteria; toward the light.

32. A flagellum is composed of 3 parts
a). Basal body associated with cytoplasmic membrane
and cell wall
b). a short hook and
c). A helical filament which is usually several times
longer than the bacterial cell.
The hook and filament are made up of protein whereas
the composition of basal body is not known. The
protein of the filament is known as flagellin.

33. Based on the arrangement of flagella, there are four
types of bacteria:
(i) Monotrichous: A single polar
flagella. e.g. Pseudomonas aeruginosa.
(ii) Lophotrichous: A cluster of polar
flagella. e.g. Pseudomonas fluorescens.
(iii) Amphitrichous: Either a single or cluster of
flagella at both the cell poles. e.g. Aquaspirillum
serpens.
(iv) Peritrichous: Flagella arranged along the sides of
the bacteria. e.g. Salmonella typhi.

35. Many species of bacteria have pili (singular, pilus), small
hairlike projections emerging from the outside cell
surface.
These outgrowths assist the bacteria in attaching to other
cells and surfaces, such as teeth, intestines, and rocks.
Without pili, many disease-causing bacteria lose their
ability to infect because they're unable to attach to host
tissue.
Specialized pili are used for conjugation, during which
two bacteria exchange fragments of plasmid DNA.

36.  Each bacterium is enclosed by a rigid cell wall composed of
peptidoglycan, a protein-sugar (polysaccharide) molecule.
 The wall gives the cell its shape and surrounds the
cytoplasmic membrane, protecting it from the environment.
 It also helps to anchor appendages like the pili and flagella,
which originate in the cytoplasm membrane and protrude
through the wall to the outside.
 The strength of the wall is responsible for keeping the cell
from bursting when there are large differences in osmotic
pressure between the cytoplasm and the environment.

37.  Most of the bacteria retain their original cells even after subjected to very
high pressure or severe physical conditions.
 It accounts for 10-40% of dry weight of the cell.
 Cell walls can be broken by sonic or ultrasonic treatment or by subjecting
the cells to extremely high pressure and subsequent sudden release of
pressure.

38.  Cell wall composition of eubacteria is different from that of archaebacteria.
 Eubacteria cell wall is made up of peptidoglycan (murein and insoluble,
porous cross linked polymer of enormous strength and rigidity.
 Peptidoglycan is basically a polymer of N-acetylglucosamine, N-
acetylmuramic acid, L- alanine, D-alanine, D-glutamate and a diamino
acid.
 The peptidoglycan is present only in prokaryotes.
 The cell walls of archaebacteria are generally made up of proteins,
glycoproteins or polysaccharides.

39.  Cell wall composition varies widely amongst bacteria and is one of the most
important factors in bacterial species analysis and differentiation.
 For example, a relatively thick, meshlike structure that makes it possible to
distinguish two basic types of bacteria.
 A technique devised by Danish physician Hans Christian Gram in 1884, uses a
staining and washing technique to differentiate between the two forms.
 When exposed to a gram stain, gram-positive bacteria retain the purple color of
the stain because the structure of their cell walls traps the dye.
 In gram-negative bacteria, the cell wall is thin and releases the dye readily when
washed with an alcohol or acetone solution.

42. CYTOPLASMIC MEMBRANE
PROTOPLAST AND SPHAEROPLAST
MESOSOMES
CYTOPLASM
CHROMOSOME
RIBOSOMES
SPORES
CONIDIOSPORES AND SPORANGIOSPORES
CYSTS

43.  This is about 7.5 ηm thick and is immediately beneath the cell wall.
 This is primarily composed of phospholipids (20-30%) and proteins (60-70%).
 This membrane contains various enzymes involved in respiratory metabolism and in
the synthesis of capsular and cell wall components.
 It is the site of generation of proton motive force, which drives ATP synthesis,
certain nutrient transport systems and flagellar motility.
 Damage to this membrane may result in the death of the cell.

44.  A protoplast is that portion of a bacterial cell
consisting of the cytoplasmic membrane and
the cell material bound by it.
 This can be prepared from Gram positive bacteria
by treating the cells with an enzyme such as
lysozyme, which selectively dissolves the cell
wall or by culturing the bacteria in the presence of
an antibiotic such as penicillin.

45.  Sphareoplast is a protoplast
surrounded by the outer
membrane of cell wall.
 In gram-negative bacteria only
peptidoglycan layer can be
removed but outer membrane is
still intact surrounding the
protoplast

47. • In many bacteria, especially Gram-
positive bacteria, the cytoplasmic
membrane appears to be infolded at
more than one point.
• Such infoldings are called
mesosomes.
• Mesosomes are thought to be
involved in DNA replication, cell
division and export of exocellular
enzymes.

48.  The cytoplasm, or protoplasm, of bacterial cells is where the functions for cell
growth, metabolism, and replication are carried out.
 It is a gel-like matrix composed of water, enzymes, nutrients, wastes, and
gases and contains cell structures such as ribosomes, a chromosome, and
plasmids.
 The cell envelope encases the cytoplasm and all its components.
 Unlike the eukaryotic (true) cells, bacteria do not have a membrane enclosed
nucleus.
 The chromosome, a single, continuous strand of DNA, is localized, but not
contained, in a region of the cell called the nucleoid.
 All the other cellular components are scattered throughout the cytoplasm

49.  Volutin granules (reserve source of phosphate), poly-β-
hydroxybutyrate (PHB) and glycogen (both serving as source
of carbon and energy) are some of the granules present in the
cytoplasm of some bacteria.
 Gas vesicles are present in bacteria that grow in aquatic
habitat

51.  The nucleoid is a region of cytoplasm where the chromosomal DNA is located.
 It is not a membrane bound nucleus, but simply an area of the cytoplasm where the
strands of DNA are found.
 Most bacteria have a single, circular chromosome that is responsible for replication,
although a few species do have two or more.
 Smaller circular auxiliary DNA strands, called plasmids, are also found in the
cytoplasm.

52. The very existence of plasmids in bacterial cytoplasm was revealed by
Lederberg in 1952 while working on conjugation process in bacteria.
A plasmid is a small, circular piece of DNA that is different than the
chromosomal DNA, which is all the genetic material found in an organism’s
chromosomes.
It replicates independently of chromosomal DNA.
Plasmids are mainly found in bacteria, but they can also be found in archaea
and multicellular organisms.
Plasmids usually carry at least one gene, and many of the genes that plasmids
carry are beneficial to their host organisms.

53.  Ribosomes are 70 S type
consisting of 50 S and 30 S sub-
units.
 Some ribosomes are free in the
cytoplasm and some are
attached to inner surface of the
cytoplasmic membrane.

54.  Spore is a metabolically dormant form,
which under appropriate conditions can
undergo germination and grow out to
form a vegetative cell.
 Spores produced within the cell are
called endospores and the spores
produced external to cell are called
exospores.

55. Endospores are thick walled, highly refractile bodies
that are produced (one per cell) by Bacillus,
Clostridium, Sporosarcina and few other genera.
They are generally formed at the end of the active
growth or during stationary phase.
 They are extremely resistant to desiccation, staining,
disinfecting chemicals, radiation and heat.

56.  Exospores are formed external to the vegetative cell by budding at
one end of the cell in the methane oxidizing genus Methylosinus.
 They are desiccation and heat resistant.

58. CONIDIOSPORES AND SPORANGIOSPORES
 The bacteria, actinomycetes form branching hyphae.
 From the tips of these hyphae spores develop singly or in chains.
 If the spores are contained in an enclosing sac (sporangium), they are
termed SPORANGIOSPORES, if not they are called CONIDIOSPORES.
 These spores can survive long periods of drying but they do not have high
heat resistance.

60. • thick walled, desiccation resistant, dormant forms that
develop by differentiation of vegetative cells.
• EX: AZATOBACTER

63. • Draw a neat labelled diagram of bacterial cell and explain the internal and external
structures of the bacterial cell.
• Explain the types of flagella with diagrams and examples
• Write the difference between
1. Eukaryotic cell and Prokaryotic cell
2. Gram positive and Gram negative cell walls
3. Endospore and Exospores
4. Spore and Cysts
5. Flagella and Pili
6. Protoplast and Sphaeroplast