Ultra structure of Bacteria

1. Ultra structure of Bacteria
Adhithya Madhavan KS
1st Msc Botany

3. • Gram positive bacteria
• Gram-positive bacteria are the genus of the bacteria family and a member of
the phylum Firmicutes.
• These bacteria retain the colour of the crystal violet stain which is used during
gram staining.
• These bacteria give a positive result in the Gram stain test by appearing purple
coloured when examined under a microscope, hence named, gram-positive
bacteria.
• Gram-positive bacteria can be staphylococci, streptococci, pneumococci,
Bacillus anthracis, and Corynebacterium diptheriae.

4. • Gram negative bacteria
• Gram negative bacteria are the genus of bacteria family and a member of
the phylum Firmicutes.
• They are the group of aerobic bacteria which does not retain the crystal
violet dye during the procedure of Gram staining and appear pink in colour
when examined under the microscope
• The gram-negative bacteria include the model organism Escherichia coli, as
well as many pathogenic bacteria, such as Pseudomonas aeruginosa,
Chlamydia trachomatis, and Yersinia pestis.

5. • As bacterial cells are very minute, they are studied under electron microscope in
which it reveals various structures.
• It includes both external and internal structures
• STRUCTURE EXTERNAL TO THE CELL WALL
1. Flagella:-
• The motile form of bacteria swim by means of small flexible whip like appendages
called flagella.
• They are much thinner and measures about 120A° thick and 4-5 long
• Chemically they are made up of protein named flagellin

6. Ultra structure of flagellum
Flagellum is structurally differentiated in to three parts
Basalbody:
• It is a small rod like structure which is attached deep in the cytoplasm of
the bacterial cell
• In gram-ve bacterium it possesses two sets of rings (i) a proximal set (ii)
a distal set. Each set consist of two pairs of ring
• Outer pair is attached to the cell wall while inner pair is attached to the
cell membrane.
• Two pairs of rings i.e. four rings are L-(lipopolysaccharide) ring, P-
(peptidoglycan) ring, S-(super membrane) ring, and M-(membrane) ring.

7. • The flagellum of gram positive bacterium lacks the outer set of
ring.
• Gram-positive bacteria have a single pair of rings. The S-ring is
attached to inside thick layer of peptidoglycan and M-ring is
attached to cell membrane
• Main function is to synthesis the polymers of flagellum and
regulation of movement

8. Hook
• It connect the basal body and the main filament
• The length of hook of gram negative bacterium is shorter than
gram positive
• Functionally they provide shape to the flagellum
Filament
• This is a tubular structure attached to the hook, made up of
globular protien subunits
• Main function of flagella is to provide motility

9. Structure of
flagella

10. Pili or fimbrae
• These are hair like appendages present on the surface Of most of
the gram negative bacteria
• They are smaller than flagella and have no role in motility
• Their origin is from cytoplasm and penetrate through the
peptidoglycan layers of the cell wall
• Chemically they are composed of 100% protein named fimbrilin

11. Mainly two types of pili are found in bacteria
• Somatic pili
• Sex pili or conjugate pili
Functions:
• They bear antigenic properties
• Sex pili helpful in chromosome transfer
• Somatic pili helps the bacterium for attachment to a substratum

13. Capsules
• Some bacterial cells are surrounded by a viscous substances
forming a covering layer or envelop around the cell wall called
capsule
• They are usually composed of polysaccharides
• It is rigid and organised
• They are resistant to phagocytosis
• Protect from desiccation
• Seen mostly in gram negative bacteria (E. Coli)

14. Slime layers
• Slime layer is an extracellular material secreted by some bacteria
and they are loosely associated with bacterium and easily washed
off and they are unorganized
• Glycoclayx are more deformed And not well organized

17. Cell wall
• This is a very rigid structure and provide definite shape to the cell
• Since most of the bacterium lives in hypotonic environment, this
cell wall prevent the cell from expanding and bursting
• It can resistant to extremely high pressure
• Cell wall is very essential for the growth and division of bacteria
• The most important constituent of cell wall is the peptidoglycan
and it is a polymer of NAG and NAM

18. Wall of gram positive and gram negative bacteria
• Gram positive bacteria have much greater amount of peptidoglycan in
their cell wall
• Cell wall of measures 30 – 80 nm in thickness
• Teichoic acid or acidic polysaccharides are mainly present in gram
positive bacteria
• Teichoic acid is a negatively charged substitute polysaccharides
polymer made up of ribitol and glycerol joined through diphosphoester
linkages
• It is hydrophilic and it’s main function is to transport positive charges
substances to the bacterial cell in the storage phosphorus

19. Cell envelope of gram negative bacteria
• There are 3 principle layers in the envelope, the outer membrane,
peptidoglycan cell wall and the inner membrane
• Theoutermost membrane is known as cell wall while the inner one is referred
as cytoplasmic membrane.
• The two concentric membrane layer which delimit an aqueous cellular
compartment called periplasm
Outer membrane:
• Starting from the outside and preceding inward the first layer encountered is
the outer membrane, it is a distinguishing feature of gram negative bacteria

20. • The membrane is bilayered structure consisting mainly of
phospholipids protein and lipopolysaccharide (L.P.S.).
• It serves as a protective barrier
Inner membrane (Cytoplasmic membrane)
• Inner membrane Is a phospholipid bilayer
• The cytoplasmic membrane act as a hydrophobic barrier for the
penetration of most

22. • Ribosomes : Ribosomes are found in free floating conditions and are
randomly distributed in the cytoplasm.
• During protein synthesis a number of ribosomes are held together by
mRNA and form polyribosomes.
• The number of ribosome is directly proportional to the rate of protein
synthesis.
• The ribosome of prokaryote are of 70s type,each 70s ribosome is
composed of two subunits larger 50S and a smaller 30S. At low
concentration of Mg+2 ions these 70S ribosome is dissociated into its
two subunits.
• Ribosome of E. coli bacteria is made up of 63% RNA and 37% protein or
they are in 2:1 ratio.

23. Endospore
• Endospore formation occurs in bacteria to tide over unfavorable environmental
conditions. They are produced under conditions of limited supply of carbon,
nitrogen and phosphorous.
• This process was first of all reported by Cohn (1817) and late by
Koch (1877).
• Endospores are generally formed in bacteria pathogenic to plants, animals and
human beings.
• Endospores are heat, chemical, drying, freezing and radiation resistant bodies.
• They can survive under dormancy even upto 50 years and on getting favorable
environmental conditions they may germinate to start a new bacterial life.

24. • Endospores are found in bacteria like Bacillus, Clostridium,
Sporolactobacillus,
• Thus endospore is a highly resistant structure. The resistant nature is due
to
following reasons:
(i) Lowest metabolic activities.
(ii) Very few amount of water.
(iii) Impermeable and protective nature of spore coat.
(iv) Lack of active enzymes.
(v) High percentage of Ca+2 ion in spore composition.

26. Thank you