bacteria shape size and reproduction

1. Bacteria: Shape, Size and Reproduction
By
Padmashree Das
Roll No: 01/16
M.Sc Microbiology
Dept. of Botany
Gauhati University

2. Bacteria
 Bacteria (singular: bacterium) constitute a large
domain of prokaryotic microorganisms.
 The study of bacteria is known as bacteriology, a
branch of microbiology.
 Bacteria was first discovered by Antony van
Leeuwenhoek in 1970s.

3. Bacterial Morphology Arrangement
1. Bacilli (Rod-shaped forms)
a. Streptobacilli
b. Bacilli
2. Cocci (Spherical forms)
a. Cocci
b. Diplococci
c. Streptococci
d. Staphylococci
e. Tetrads
f. Sarcina

4. Common Shapes & Arrangement

5. Bacterial Morphology Arrangement
3. Spiral (Helical forms)
a. Vibrio
b. Spirillum
c. Spirochete

6. Bacterial Cell Structures &
Functions

7. Size relationships among
prokaryotes

8. Bacterial Cell Structure

9. Bacterial Cell Structure
 Appendages - flagella, pili or fimbriae
 Surface layers - capsule, cell wall, cell
membrane
 Cytoplasm - nuclear material, ribosome,
mesosome, inclusions etc.
 Special structure - endospore

10. Appendages
1. flagella
Some rods and spiral form have this.
a). function: motility
b). origin : cell membrane flagella attach to the cell
by hook and basal body which consists of set(s) of rings
and rods
Gram -ve : 2 sets of ring and rods
e.g. E. coli
Gram +ve : one set of ring and rod
e.g. B. megaterium

11. Organ of bacterial locomotion
Ultra structure of
Structure of the
flagellum

12. Flagella movement

13. Flagella movement

14. b).Origin (continued)
– The structure of the bacterial flagella allows it to spin
like a propeller and thereby propel the bacterial cell;
clockwise or counter clockwise ( Eucaryotic , wave
like motion.
– Bacterial flagella provides the bacterium with
mechanism for swimming toward or away from
chemical stimuli, a behavior is known as
CHEMOTAXIS, chemosenors in the cell envelope
can detect certain chemicals and signal the flagella to
respond.

15. c). Position of the flagellum
monotrichous
lophotrichous
peritrichous
d). Structure of the flagellum
protein in nature: subunit flagellin

16. 2. Pili or Fimbriae
Shorter than flagella and straighter , smaller.
Found only on some gram-ve bacteria.
a). function: adhere. One of the invasive
mechanism on bacteria. Some pathogens
cause diseases due to this. If mutant,
(fimbriae) is not virulent. Prevent
phagocytosis.

17. Pili - sex factor. If pili are present then the strain
is named as F+ and if pili are absent then it is
known as F- factor.
It is necessary for bacterial conjugation
resulting in the transfer of DNA from one cell to
another. It have been implicated in the ability of
bacteria to recognize specific receptor sites on
the host cell membrane. In addition, number of
bacteria virus infect only those bacteria have F
pilus.

18. b). Origin of Pili: Cell membrane
c). Position: common pili , numerous over
the cell, usually called fimbriae sex pili, 1-
4/cell
d). Structure: composed of proteins which can
be dissociated into smaller unit
Pilin . It belongs to a class of protein Lectin
which bond to cell surface polysaccharide.

19. II. CELL SURFACE LAYER
1. Capsule or slime layer
Many bacteria are able to secrete material
that adheres to the bacterial cell but is
actually external to the cell.
It consists of polypeptide and
polysaccharide on bacilli. Most of them
have only polysaccharide. It is a protective
layer that resists host phagocytosis.
Medically important.

20. 2. Bacterial Cell Wall
General structure: mucopolysaccharide
i.e. peptidoglycan. It is made by N-
acetylglucosamine and N-acetylmuramic acid.
tetrapeptide ( L-alanine- isoglutamine-lysine-
alanine) is attached. The entire cell wall
structure is cross linked by covalent bonds.
This provide the rigidity necessary to maintain
the integrity of the cell.
N-acetylmuramic acid is unique to
prokaryotic cell.

21. Cell walls of bacteria
Under Electron micrograph (Cell wall)

22. Cell walls of bacteria
Scanning Electron Micrograph (SEM Image)

23. Cell walls of bacteria

24. Structure and Chemical composition of Bacterial
cell wall
 Peptido-glycan Polymer
(amino acids + sugars)
 Sugars; NAG & NAM
 N-acetylglucosamine
(G)
 N-acetylmuramic acid
(M)

25. Structure of peptidoglycan

26. Gram positive bacterial cell wall
 Thick peptidoglycan layer
 Pentaglycin cross linkage.
 Teichoic acid: ribitol TA &
glycerol TA
 Some have peptioglycan
teichoic acid.
 All have lipoteichoic acid.

27. Function of TA:
* Antigenic determinant
* Participate in the supply of Mg to the
cell by binding Mg++
* Regulate normal cell division.

28. Structure of the Gram-positive
Cell Wall

29. Bacteria can reproduce in one of two ways:
1. Asexually
2.Sexually
Transduction
Binary Fisiion Conjugation
BACTERIAL REPRODUCTION

30. Bacterial Reproduction
Binary Fission
Binary = 2
Fission = split
apart
Asexual
reproduction
Occurs after a
period of growth

31. Binary Fission Steps
1. DNA replication (time
frame is minutes or
hours)
2. Protein synthesis (~ 40
minutes)
3. Replication of structures
(7 minutes)
4. Cytoplamic separation (7
minutes)
5. New cell walls form (7
minutes)

32. Bacterial Conjugation
• plasmid copies itself
• passes through pili
(cytoplasmic bridge)
into recipient cell
•cells separate with
both cells containing
the plasmid
plasmid
donor recipient
cell (+) cell ( - )
pili

33. TRANSFORMATION
 In transformation, the living cell picks up
DNA that have been released by dead
cells. Thus the living cell gets additional
DNA.
 Bacterial transformation was first
discovered by Griffith in 1928

34. TRANSDUCTION
 In transduction, fragments of DNA are carried
from one bacterial cell to another by bacterial
viruses.
 Transduction is of two types- generalised and
specialized.
 In generalised transduction, the
bacteriophages may transfer any bacterial
genes.
 In specialized transduction, a particular
bacteriophage strain can transfer only certain
genes.

35. Generation Time
Genetically determined, different species
different times to undergo binary fission
Ex: E. coli = 20 minutes
Environment also determines the
generation time (cold temperatures slow
it down).

36. Thank You