4. Prokaryotes (Bacteria)
• Eubacter "True" bacteria
– human pathogens
– clinical or environmental
– one kingdom
• Archaea
– Environmental organisms
– second kingdom
4
5. Introduction
• Bacteria despite their simplicity, contain a
well developed cell structure which is
responsible for many of their unique
biological properties. Many structural
features are unique to bacteria and are not
found among eukaryotes.
6. Cell Morphology
• The most elemental structural property of bacteria is cell
morphology (shape).
• Bacteria are classified by shape into three basic groups:
• cocci (spherical)
• bacilli (rod-like)
• spirochetes (spiral)
• Some bacteria are variable in shape and said to
pleomorphic.
• The shape of a bacteria is determined by its rigid cell wall.
• The microscopic appearance of a bacterium is one of the
most important criteria used in identification.
8. • The arrangement of bacteria is important.
Example:
• Cocci in pairs (diplococci)
• Cocci in chains (streptococci)
• Cocci in clusters (staphylococci)
9. Bacteria Size
• Bacteria range in size from about 0.2 to 5
um.
• The smallest bacteria (Mycoplasma) are the
same size as a large virus.
• The longest bacteria rods are the same size
as some yeasts and human red blood cells.
10. CLASSIFICATION OF
BACTERIA
• ON BASIS OF SHAPE
• ON BASIS OF ARRANGEMENT
• ON BASIS OF STAINING
• ON BASIS OF OXYGEN
REQUIREMENT
10
21. Cell envelope
– The cell envelope: Consists
of cell membrane and cell
wall plus an outer
membrane if present.
– Most bacterial cell
envelopes fall into two
major categories: Gram
positive and Gram
negative based on Gram
staining characteristics
that reflect major
structural differences 21
between the two groups
26. Cell wall
• Cell wall consists of
the peptidoglycan layer
attached structures
(eg: capsule, pili etc)
26
27. PEPTIDOGLYCANS ( murein/ mucopeptide)
– Multilayered in gram positive bacteria.
– Surrounds the bacterial cell membrane.
– Provides rigidity. It is huge (billions in molecular weight)
– Consists of a glycan (polysaccharide) backbone with peptide
side chains.
– PG is found in all bacteria except Chlamydia and
Mycoplasma.
27
28. Gram positive cell
envelope:
Thick peptidoglycan
with covalently bound
teichoic acid.
These negatively
charged molecules
concentrate metal
ions from the
surroundings.
Lipoteichoic acid is
primarily associated
with the cell
membrane. 28
35. Capsules and slime layers
(Glycocalyx)
• well defined: capsule
• outside cell envelope
• usually polysaccharide (in B. anthracis– D
glutamate)
• Gives virulance (antiphagocytic).
• Antigenic (vaccine formation).
• Adherence.
• Quellung reaction (Identification).
2. not well defined-- slime layer or glycocalyx
o Adherence
35
o S.mutans (Plaque formation)
36. FLAGELLA
• For motility – long & whip like
• Subunits—Flagellin
• Respond to food/poison –chemotaxis
• Never present in cocci.
• Use ATPs – proton motive force
• Number and location of flagella.
(Peritrichous, monotrichous,
lophotrichous, axial). 36
37. • Flagella
–embedded in cell membrane
–project as strand
–Flagellin (protein) subunits
–move cell by propeller like action
–*axial filament
–*flagellar antigen
37
40. Pili (fimbriae)
•Short , hair-like projections of the cell
•Protein--pilin
•Mostly on gram-ve bacteria
•adhesion to host epithelium
•Two types– ordinary pili
sex pili
•sexual conjugation (sex pili)
40
41. Endospores (spores)
• Metabolically dormant cell
• Produced when adverse conditions eg starved –
sporulation – bacterial DNA, cytoplasm, cell
membrane, peptidoglycans, water & keratin- like coat
• Resistant to adverse conditions
- high temperatures (not killed by boiling),
- radiation, dehydration
- organic solvents
• Killed by autoclaving (121 C for 30 min)
• contain dipicolinic acid
• Bacillus (central) and Clostridium (terminal)
• Survival for many years 41
42. CYTOPLASM
Granules
– Storage of nutrients
– Stained with dyes
Transposons
Jumping genes – within DNA or between DNAs of
bacteria, plasmids & bacteriophages
Pieces of DNA
No independent replication.
Can be more than one in 1 DNA.
For toxins, enzymes, antibiotic resistance etc.
4 domains– inverted repeats, transposase, repressor,
resistance. 42
43. Plasmids
Multiple copies in number
Extra-chromosomal DNA, double
stranded, circular
Can be incorporated in DNA
Coding pathogenesis and antibiotic
resistance, heavy metal & U-V light
resistance, toxins, pili etc.
Replication independent of bacterial
chromosome.
Transmissable & Non transmissable. 43
44. Making Wall-less forms
• Result from action of:
– enzymes lytic for cell wall (eg lyzozyme)
– antibiotics inhibiting peptidoglycan biosynthesis
• Wall-less bacteria that don’t replicate:
– spheroplasts (with outer membrane) gram - ve
– protoplasts (no outer membrane) gram +ve.
• Wall-less bacteria that replicate
– L forms ( relative resistance to antibiotics)
44
48. Procedure
of Gram Staining
• Developed by Christian Gram
• In 1884
• 4 steps:
Stain with Crystal voilet (primary stain)
Then pour Gram,s iodine (mordant)
Decolourize
Pour Safranin (counter stain)
48
the bacterial cell wall provides structural integrity to the cell. In prokaryotes, the primary function of the cell wall is to protect the cell from internal turgor pressure caused by the much higher concentrations of proteins and other molecules inside the cell compared to its external environment. The bacterial cell wall differs from that of all other organisms by the presence of peptidoglycan (poly- N -acetyl glucosamine and N -acetylmuramic acid), which is located immediately outside of the cytoplasmic membrane. Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell shape. It is relatively porous and is not considered to be a permeability barrier for small substrates. While all bacterial cell walls (with a few exceptions e.g. intracellular parasites such as Mycoplasma ) contain peptidoglycan, not all cell walls have the same overall structures. Since the cell wall is required for bacterial survival, but is absent in eukaryotes, several antibiotics (penicillins and cephalosporins) stop bacterial infections by interfering with cell wall synthesis, while having no effects on human cells.
