Download Cell wall

Bacterial Morphology and
Structure
SIZE OF BACTERIA
• Unit for measurement :
Micron or micrometer,μm: 1μm=10-3mm
• Size:
Varies with kinds of bacteria, and also
related to their age and external
environment.
Shape of Bacteria
• Cocci: sphere, 1μm
• Bacilli: rods , 0.5-1 μm in width -3 μm in length
• Spiral bacteria: 1~3 μm in length and 0.3-0.6 μm in width
Coccus
Bacillus
Spiral Bacterium
Structure of
Bacteria
Essential structures 基本结构
cell wall 细胞壁
cell membrane 细胞膜
Cytoplasm 细胞质
nuclear material 核质
Particular structures 特殊结
构
capsule 荚膜
flagella 鞭毛
pili 菌毛
spore 芽胞
Cell wall
• Situation: outmost portion. 15-30nm in
thickness, 10%-25% of dry weight.
1884: Christian Gram: First publication for the Gram stain method)
Editor's note: I would like to testify that I have found the Gram method to be one of
the best and for many cases the best method which I have ever used for staining
Schizomycetes.
Gram, C. 1884. Ueber die
isolirte Farbung der
Schizomyceten in
SchnittÄund
Trockenpraparaten.
Fortschritte der Medicin,
Vol. 2, pages 185-189.
Cell wall :Common peptidoglycan
layer
• A backbone of N-acetyl glucosamine and
N-acetylmuramic acid: Both discovered in
Gram positive and Gram negative bacteria.
• A set of identical tetrapeptide side chain
attached
to
N-acetyl-muramic
acid:
different components and binding modes
in Gram positive and Gram negative
bacteria.
• A set of identical peptide cross bridges:
only in Gram positive bacteria
NAM
NAG
NAM
NAG
CH2OH
CH2OH
CH2OH
CH2OH
H
H
O
O
O
O
H
H
O
O
H
H
H
H
O H
OH H
O H
OH H
O
O
H
H3C
H3 C
H NH H
H NH
H NH H
H NH H
C–H
C–H O=C
O=C
O=C
O=C
C=O CH3
CH3
CH3
C=O CH3
H– N
H– N
L–Ala
L–Ala
D–Glu
L–Lys
D–Ala
C=O
图附
H
Gly–Gly–Gly–Gly–Gly–N
D–Glu
L–Lys
D–Ala
C=O
H
Gly–Gly–Gly–Gly–Gly–N
溶菌酶作
用位点
青霉素作
用位点
G
G
M
M
谷
丙
丙
DAB
G
谷 丙
DAB
丙
G
Special components of Gram
positive cell wall
-
Teichoic acid
Special components of
Gram negative cell wall
Functions of Cell Wall
• Maintaining the cell's characteristic shape- the
rigid wall compensates for the flexibility of the
phospholipid membrane and keeps the cell
from assuming a spherical shape
• Countering the effects of osmotic pressure
• Providing attachment sites for bacteriophages
• Providing a rigid platform for surface
appendages- flagella, fimbriae, and pili all
emanate from the wall and extend beyond it
• Play an essential role in cell division
• Be the sites of major antigenic determinants of
the cell surface。
Wall-less forms of Bacteria.
• When bacteria are treated with 1) enzymes that are
lytic for the cell wall e.g. lysozyme or 2) antibiotics
that interfere with biosynthesis of peptidoglycan,
wall-less bacteria are often produced.
• Usually these treatments generate non-viable
organisms. Wall-less bacteria that can not replicate
are referred to as spheroplasts (when an outer
membrane is present) or protoplasts (if an outer
membrane is not present).
• Occasionally wall-less bacteria that can replicate
are generated by these treatments (L forms).
Bacteria L form
• Bacteria with dfective cell wall-bacterial
L form: protoplast, spheroplast
Cell membrane
Function of Cell membrane
a. Selective permeability and
transport of solutes into cells
b. Electron transport and oxidative
phosphorylation
c. Excretion of hydrolytic exoenzymes
d. Site of biosynthesis of DNA, cell
wall polymers and membrane lipids.
Mesosomes
•
Mesosomes are specialized structures
formed by convoluted inveigh-nations of
cytoplasmic membrane, and divided into
septal and lateral mesosome.
Cytoplasm
• Composed largely of water, together with
proteins, nucleic acid, lipids and small
amount of sugars and salts
• Ribosomes: numerous, 15-20nm in diameter
with 70S; distributed throughout the
cytoplasm; sensitive to streptomycin and
erythromycin site of protein synthesis
• Plasmids:
extrachromosomal
genetic
elements
• Inclusions: sources of stored energy, e,g
volutin
Ribosomes
• Ribosomes are the
protein
synthesizing
factories of the cell.
• They translate the
information in
mRNA into protein
sequences.
Plasmid
Plasmids are small，
circular/line，
extrachromosomal，
double-stranded DNA
molecules。They are
capable of self-replication
and contain genes that
confer some properties，
such as antibiotic resistance，
virulence factors。
Plasmids are not essential
for cellular survival.
Inclusions of
Bacteria
• Inclusions are aggregates of various
compounds that are normally involved in
storing energy reserves or building
blocks for the cell. Inclusions accumilate
when a cell is grown in the presence of
excess nutrients and they are often
observed under laboratory conditions.
granulose
Nucleus
• Lacking nuclear membrane, absence of
nucleoli, hence known as nucleic
material or nucleoid, one to several per
bacterium.
Capsules and slime layers
• These are structures surrounding the outside of the
cell envelope. When more defined, they are referred to
as a capsule when less defined as a slime layer. They
usually consist of polysaccharide; however, in certain
bacilli they are composed of a polypeptide
(polyglutamic acid). They are not essential to cell
viability and some strains within a species will produce
a capsule, whilst others do not. Capsules are often lost
during in vitro culture.
Capsules and slime layers
Capsules and slime layers
Function of Capsules and slime layers(1)
• Attachment :These structures are thought to help
cells attach to their target environment.
Streptococcus mutans produces a slime layer in the
presence of sucrose. This results in dental plaque
and many bacteria can stick to tooth surfaces and
cause decay once S. mutans forms a slime layer.
Vibrio cholerae, the cause of cholera, also produces
a glycocalyx which helps it attach to the intestinal
villi of the host.
Function of Capsules and slime layers(2)
• Protection from phagocytic engulfment.
Bacterial pathogens are always in danger of
being "eaten" by phagocytes. (Host cells that
protect you from invaders.) Streptococcus
pneumoniae, when encapsulated is able to
kill 90% of infected animals, when nonencapsulated no animals die. The capsule
has been found to protect the bacteria by
making it difficult for the phagocyte to engulf
the microbe.
Function of Capsules and slime layers(3)
• Resistance to drying. Capsules and slime
layers inhibit water from escaping into the
environment.
Function of Capsules and slime layers(4)
• Reservoir for certain nutrients. Glycocalyx
will bind certain ions and molecules.
These can then be made available to the
cell.
Function of Capsules and slime layers(5)
• Depot for waste products. Waste products
of metabolism are excreted from the cell,
and will accumulate in the capsule. This
binds them up, and prevents the waste
from interfering with cell metabolism.
Flagella.
• Some bacterial species are mobile and possess
locomotory organelles - flagella. Those that do are able
to taste their environment and respond to specific
chemical foodstuffs or toxic materials and move towards
or away from them (chemotaxis). Flagella are
embedded in the cell membrane, extend through the
cell envelope and project as a long strand. Flagella
consist of a number of proteins including flagellin. They
move the cell by rotating with a propeller like action.
Relative Speeds of Organisms
Organism
Cheetah
Human
Bacteria
Kilometers per hour
111
37.5
0.00015
Body lengths per second
25
5.4
10
Flagella
• The diameter of a flagellum is thin, 20 nm,
and long with some having a length 10 times
the diameter of cell. Due to their small
diameter, flagella cannot be seen in the light
microscope unless a special stain is applied.
Bacteria can have one or more flagella
arranged in clumps or spread all over the cell.
Flagella
•
•
•
•
Monotrichate
Amphitrichate
Lophotrichate
Peritrichate
Flagella
Function of Flagella
• Identification
of Bacteria
• Pathogenesis
• Motility of
bacteria
Pili
• Pili are hair-like projections
of the cell , They are known to be receptors for
certain bacterial viruses.
• Chemical nature is pilin
• Classification and Function
a. Common pili or fimbriae: fine , rigid numerous,
related to bacterial adhesion
b. Sex pili: longer and coarser, only 1-4, related
to bacterial conjugation
Sex pili
•
•
A donor bacteria will attach to a recipient via
the sex pilus. Then a copy of part of the
donor bacterium's genome passes through
the sex pilus into the recipient.
Conjugation, as it is called, is one
explanation for the rapid spread of drug
resistance in many different species of
bacteria.
Common pili or fimbriae
• Pili have also been show to be important for the
attachment of some pathogenic species to their host.
Neisseria gonorrheae, the causative agent of
gonorrhea, has a special pili that helps it adhere to
the urogenital tract of its host. The microbe is much
more virulent when able to synthesize pili.
Endospores
• Endospores are highly resistant resting
structures produced within cells. They are
common to organisms which live in soil and
may need to wait out some rough times such
as >100°C heat, radiation, drying or
chemical agents ; under favourable
conditions , a spore germinates into a
vegetative cell
• Spores are commonly found in the genera Bacillus
and Clostridium.
DPA and survive
• Dipicolinic acid,DPA.
• Spores can survive for a very long time, and
then regerminate. Spores that were dormant
for thousands of years in the great tomes of
the Egyption Pharohs were able to germinate
and grow when placed in appropriate medium.
There are even claims of spores that are over
250 million years old being able to germiinate
when placed in appropriate medium. These
results have yet to be validated.
Spores
• The mechanisms that
acount for this include
the dehydration of the
protoplast and the
production of special
proteins that protect
the spores DNA.
• are capable of detecting their environment and under
favorable nutrient conditions germinating and returning to
the vegetative state.
Spore
• Identification of Bacteria
• Pathogenesis
• Resistance
Methods
Microscopey
•
•
•
•
Light Microscope
Electron Microscope
Darkfield Microscope
Phase Contrast
Microscope
• Fluorescence
Microscope
• Cofocal Microscope）
Methods
Staining Methods
• Simple staining;
• Differential staining ( Gram stain,
Acid-fast stain),
• Special staining( Negative stain,
Spore stain, Flagella stain)