Download The Bacterial Cell Envelope I. The cell envelope Glycocalyx

Bio 280 The Bacterial Cell Envelope
The Bacterial Cell Envelope
I. The cell envelope
Made up of (moving
I. The cell envelope -- what it consists of
inward):
ä
II. Glycocalyx
Glycocalyx (not on
all bacteria)
ä
Outer ____________
(not on all bacteria)
III. Structure of the cell wall
III. Gram-positive vs. Gram-negative cell
envelopes
ä
________ ________
ä
Cytoplasmic (or
“plasma” or “cell”)
Bacillus megaterium
membrane
Glycocalyx
Capsule
Polysaccharide (sometimes combined with
protein) layer outside the cell.
Two types. Neither is necessary for cell
survival.
ä ___________
____________ -- loose. Protects
from loss of ____________ and some nutrients.
ä __________
-- bound more tightly, thick,
Brucella species -- causal agents of ___________ __________ and
gummy.
_________________ ____________________
Capsule stain
Capsule stain of Enterobacter aerogenes
Encapsulated bacteria are apparently more difficult for
___________________ cells of the immune system to
recognize and destroy
Examples
Streptococcus pneumoniae is able to initially evade phagocytosis
and cause infections such as pneumococcal pneumonia, sinusitis,
otitis media, and meningitis because of its capsule.
ä Encapsulated strains of Hemophilus influenzae type b can cause
severe respiratory infections, septicemia, epiglottitis, and
meningitis in children.
(Other unencapsulated strains of H. influenzae usually cause mild
respiratory infections such as sinusitis and otitis media.)
ä Other encapsulated bacteria include Neisseria meningitidis (causes
meningitis) and Bordetella pertussis (causes pertussis).
ä
Note colorless capsules surrounding purple rods
www.cat.cc.md.us/~gkaiser/lecguide/unit1/u1iic.html
Bio 280 The Bacterial Cell Envelope
Another function of glycocalyx -biofilm formation
Biofilms (cont.)
Streptococcus mutans
Converts ___________ --> glucose (& fructose) -
Biofilm --
-> _____________ (polysaccharide glycocalyx) --
Microbial
colonies encased
in an adhesive,
usually
______________
material, and
attached to a
_____________.
> ________ ___________.
human dental plaque exposed to 5%
sucrose for 5 minutes after which
Gram's iodine was applied
Biofilm formed on an indwelling vascular catheter
Nancy Khardori and Mahmoud Yassien
www.mcat.net/biofilms/biofi_1.htm
Tartar magnified 7,000x to
show bacterial biofilm
www.buckman.com/eng/biofilm-all.htm
Peptidoglycan
Cell wall
2 monomers (building blocks):
ä
ä
The fundamental unit of the cell wall is a
N-acetylglucoasamine (NAG or just ‘G’)
N-acetylmuramic acid (NAM or just ‘M’)
____________________ polymer (in other
Polysaccharide
(NAG & NAM)
chains
words, a polysaccharide) called
peptidoglycan (peptides +
_______________________)
_____________
cross-links
Peptidoglycan (cont.)
Lysozyme
The cross-links in peptidoglycan are chains of _________ ___________
•
Discovered by Alexander ______________
in early part of this century
•
Found in tears, saliva, nasal and sinus fluids
•
Breaks bond between _________ and
__________ monomers in peptidoglycan
Bio 280 The Bacterial Cell Envelope
Top. In dilute solution, lysozyme digests wall, water enters the cell
and bursts the cytoplasmic membrane, causing cell lysis.
Bottom. In a sucrose solution, water doesn’t enter the cell and the
cell wall-less cell, called the protoplast, is released.
Penicillin
Typical Gram Pos. vs. Gram Neg. Cell
Envelopes
Gram stain of Staphylococcus aureus
Gram stain of Escherichia coli
www.cat.cc.md.us/~gkaiser/lecguide/unit1
Gram Pos. vs. Gram Neg. (cont.)
The Classical Gram Positive Cell
Envelope
___________ _________ of a Gram-Positive Cell Envelope
Bio 280 The Bacterial Cell Envelope
The Classical Gram Positive Cell Envelope (cont.)
Teichoic acid -- another component in the classical Gram
positive cell wall. Acts to reinforce the_______________ of
the wall and ______________ it to the plasma membrane.
The Classical Gram Negative Cell Envelope
• Bacteria with the classical Gram-negative cell envelopes have a
______________________ wall but also have an additional cell membrane,
the outer membrane .
• The periplasmic space is the area between the cytoplasmic membrane and
the ____________ ___________ in Gram-negative bacteria.
The Classical Gram Negative Cell Envelope (cont.)
Electron Micrograph of a Gram-Negative Cell Envelope
Lipopolysaccharide (LPS)
•
Large, complex molecules composed of polysaccharides linked to
____________________ molecules
•
Lipid portion is buried in the membrane, while polysaccharide portion
lies on the _____________________ of the cell.
Transmission electron micrograph of the P. aeruginosa PAO1
cell envelope showing the long O-side chains of the LPS
extending ~40 nm from the face of the outer membrane
(arrow). Bar = 35 nm.
Bio 280 The Bacterial Cell Envelope
Lipopolysaccharide (LPS) (cont.)
Porin Proteins
•
Composition of the polysaccharide varies among bacterial
species and even among individuals within a species
•
The polysaccharides on the surface of Gm negative
bacteria can be recognized by cells and molecules of host
immune systems during infection. Serve as antigens for
_________________ to bind to.
Neisseria gonorrhoeae, Gm neg. bacterium which causes
gonorrhea, avoids host immune system by changing its
LPS polysaccharide composition.
The outer membrane of Gm neg. bacteria restricts passage of
many molecules into cell (including penicillin) but has a
large number of protein channels which allow some
molecules in. These are called porin proteins.
•
•
Endotoxin -- LPS acts as a toxin in animal hosts. Lipid
portion is toxic, inducing ____________, shock, blood
coagulation, weakness, and inflammation. Releases when
cells ___________.
Membrane Vesicles (MVs)
Thin section of an
unidentified gramnegative bacterium
found in a freshwater
biofilm in a river near
laboratory. This
bacterium possesses a
microcapsule and is
liberating a prodigious
amount of MVs. Bar =
1 µm.
Journal of Bacteriology, August
1999, p. 4725-4733, Vol. 181,
No. 16
Diversity of Outer Membrane Surfaces on Neisseria species
N. gonorrheae . Extent of cell
surface texture slight
N. cinnerea. More surface texture and
membrane ‘blebs’ seen
Studies indicate much of the toxicity
of N. meningitidis (causative agent of
__________________ and meningitis)
arises from its release of
______________ in the form of blebs.
N. meningitidis . Note large blebs
The outer
membrane is
more
_____________
than the
cytoplasmic
membrane
Membrane Vesicles (cont.)
• ‘Bleb’ off from outer membrane of nearly all
Gram-______________ bacteria.
• Contain a complete outer membrane plus
______________, including periplasmic enzymes.
• Can ‘poke holes’ in Gram-positive and Gramnegative bacteria, but apparently only if they are
weakened by ________________________.
• Apparently don’t have an effect on cells of the
same _________________ (weakened or not).