Microbial structure (2) BC Yang Structural approach : Is it a view of artifact? For lecture only
Dec 22, 2015
Shapes
Bacillus
Coccus
Coccobacillus
Fusiform bacillus
Spirillum
Spirochete
Vibrio
Staphylococcus aureus
Pseudomonas aeruginosa
Bacillus anthracis
Vibrio cholerae
Fusiform bacilli
Spirillum volutans
Borrelia burgdorferi
BC YangFor lecture only
Structural view of bacteria (1)
Microscopic prokaryotes (no nucleus nor membrane-bound organelles)
Contain ribosomes Enfolding of the cell membrane carry on
photosynthesis & respiration Surrounded by protective cell wall containing
peptidoglycan (protein-carbohydrate) Many are surrounded by a sticky, protective coating
of sugars called the capsule or glycocalyx
BC YangFor lecture only
Structural view of bacteria (2)
One circular chromosome and some small DNA called plasmids
May have short, hairlike projections called pili on cell wall to attach to host or another bacteria when transferring genetic material
Some can move by flagella, gliding over slime they secrete ( e.g. Myxobacteria)
Some can form protective endospores around the DNA when conditions become unfavorable
BC YangFor lecture only
Structure and functionSTRUCTURE FUNCTIONCell Wall protects the cell and gives shape (5-20 atm resistant)
Outer Membraneprotects the cell against some antibiotics (only present in
Gram negative cells)
Cell Membraneregulates movement of materials into and out of the cell;
enzymes of respiration
Cytoplasm contains DNA, ribosomes, and organic compounds
Chromosome carries genetic information inherited from past generations
Plasmidcontains some genes obtain through genetic
recombination
Capsule, and slime layer
protects the cell (immune attack) and assist in attaching the cell to other surfaces
Endosporeprotects the cell against harsh environmental conditions,
(heat or drought)
Pilus (Pili) attaching to other surfaces (for genetic recombination)
Flagellum moves the cell
BC YangFor lecture only
Differences
Eukaryote ProkaryoteMajor groups Algae, fungi, protozoa, plant,
animalbacteria
Size >5 m 0.5-3m
Nuclear structures
Nucleus Classic membrane No nuclear membrane
Chromosome Diploid genome; multiple DNA Haploid, single DNA
Cytoplamic structures
Mitochondria Present Absent
Golgi bodies Present Absent
ER Present Absent
Ribosome 80S(60S+40S) 70S(50S+30S)
Cytoplamic membrane Contains sterols No sterols
Cell wall Absent or with chitin, cellulose + lipid, peptidoglycans
Reproduction Sexual and asexual Fission
Movement Complex flagellum (9+2) Simple flagellum
Respiration Via mitochondria On cytoplamic membrane
BC YangFor lecture only
Cell envelope: Cytoplamic membrane+ cell wall+ capsules + loss slime etc….
Gram-positive cells: Cytoplamic membrane+
thick peptidoglycan layer + capsules
Gram-negative cells: Cytoplamic inner
membrane+ thin peptidoglycan layer + periplamic space + outer membrane + + capsules /loss slime
BC Yang
high magnification AFM image of the surface of a single Pseudomonas putida
For lecture only
• The main component of the bacterial cell wall is peptidoglycan, a hydrated, semi-rigid polymer of two sugar derivatives: N-Acteylglucosamine (G) and N-Acetylmuramic acid (M). Bound to the sugar M are amino acids: Alanine -- Glutamic acid -- Meso-diaminopimelic acid (DAP) (Gm-) or Lysine (Gm+) -- Alanine.
BC YangFor lecture only
Glucosamine?
Teichoic acidAre found exclusively in gram positive organisms. Are formed as polymers of glycerol or ribitol through phosphodiester linkages.
http://www.cvm.uiuc.edu/courses/vp331/Structures_in_pathogenesi1.htmlBC YangFor lecture only
Synthesis of cell wall: The assembly of the wall components begins with the synthesis of precursors in the cytoplasm, their transport across the cell membrane, and their final polymerization. Eventually, penicillin-binding proteins catalyze covalent reactions that result in the extension, cross-linking between glycan strand, morphogenessis and eventual separation of the murein sacculus.
BC YangFor lecture only
Fluorescent image of the CreS-GFP/CreS hybrid strain
BC Yang
1. Crescentin : creS2. 430-residues protein3. Distinct 7-residue repetitive pattern4. coiled-coils: many fibrous proteins in eukaryotes
Gram positive in Gm+ organisms, an interbridge exists between the Lysine
molecule extending from one sugar backbone to the terminal Alanine of the second.
Gm+ organisms have cell walls that may contain as much as 90% peptidoglycan, with membrane associated proteins and Teichoic acids comprising the remaining components.
BC YangFor lecture only
Gram negative cross-linking of peptidoglycan by bond between the DAP molecule
extending from one sugar backbone and the terminal Alanine of another. typically composed of only about 10% peptidoglycan and possess an outer
membrane that houses the membrane associated proteins and LPS. The peptidoglycan lies in-between the periplasm.
BC YangFor lecture only
The acid-fast cell wall of Mycobacterium contains peptidoglycan, and a large amount of glycolipids such as
mycolic acid, arabinogalactan-lipid comlex, and lipoarabinomannan.
Large-scale molecular dynamic simulation of a lipopolysaccharide membrane solvated in a 4.2 nm water box.
Lipopolysaccharides is an amphiphile composed of three regions: O-polysaccharide (the O- or somatic-antigen), the core polysaccharide and lipid A. Lipid A is anchored in the outer membrane. LPS is also known as endotoxin.
BC Yang
lipid
saccharide
For lecture only
Endotoxins are thermostable, lipopolysaccharide components from the cell walls of viable or nonviable gram-negative microorganisms.
Measured endotoxin will include endotoxin that was derived from: 1) Any living cells that are present, 2) Cell wall debris from dead or dying cells, and 3) Outer membrane fragments that are released during cell growth.
An endotoxin unit, EU, is equivalent to approximately 200 pico-grams of endotoxin.
The LAL (Limulus Amebocyte Lysate) test for endotoxins can be sensitive down to 0.03 EU/ml
BC YangFor lecture only
鱟
Not confuse with exotoxin
BC Yang
(a) The x-ray crystal structure for the tetanus toxin showing how the amino acid chain is folded and (b) its calculated molecular surface showing sites 1 and 2, predicted binding sites for ligands.
Tetanus toxin:
For lecture only
Cytoplasmic membrane
5-10 nm unit membrane Absence of sterols, except mycoplasma Semifluid state, form mesosomes Selective permeability and transport Electron transport /oxidative ATP generation Bioxynthesis
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Phospholipids Major components of the cell
membrane Consists of two fatty acids and the
third hydroxyl group of glycerol is joined to a phosphate group
being amphipathic, having both a hydrophobic (hydrocarbons tails) and a hydrophilic region (phosphate head)
In water, they self-assemble into aggregates so that the phosphate heads make contact with the water and the hydrophobic hydrocarbon tails are restricted to water-free areas (micelle or phospholipid bilayer)
BC YangFor lecture only
How to get across the polar barrel
Bacterial membrane proteins - OmpA (left) and GlpF (right).
BC YangFor lecture only
ATP-dependent secretion systems
There are five major secretion systems.
Type I and type III secrete proteins across both the inner membrane
and the cell envelope (outer membrane) in one step; secreted proteins
do not make an intermediate stop in the periplasm. Type I systems
are composed of far fewer components than type III systems.
Type II and type III systems share a similar cell envelope component.
The type III secretion system of Gram-negative bacterial pathogens
injects virulence factors into host cells. The needle complex is drawn
on the basis of its appearance in electron-microscopy images (see
inset), with several ring structures that span the inner and outer
membranes. Very similar to flagella system
For lecture only
Bacterial secretion systems: type I, type II, and type III.
http://www.cdc.gov/ncidod/eid/vol2no4/mecsas.htm
For lecture only
The known type IV systems differ with respect to the route of substrate translocation. The A. tumefaciens T-DNA transfer system and the H. pylori CagA system are thought to export substrates in one step across the membrane directly to the eukaryotic cytosol. The B. pertussis Ptl system is thought to export PT in two steps across the cell envelope to the extracellular milieu. Secreted holotoxin then binds to the mammalian cell membrane.
http://www.blackwell-synergy.com/links/doi/10.1046/j.1365-2958.2001.02302.x/full/For lecture only BC Yang
Bacterial chromosome No nuclear membrane
Small polyamines and magnesium, histone-like
Lack of mitotic apparatus; fission
~3 x 109bp (1mm long), supercoiled state, single haploid
Circular (most bacteria) or linear (Streptomyes sp.)
Associated with mesosomeDNA spread of E. coli
BC YangplasmidFor lecture only
may stay inactive several years, then re-activate when conditions favorable
BC Yang
Calcium bound to dipicolinic acidKeratin-like protein coat
Ca+2
Spores
For lecture only
1. the bacterium senses that its home or habitat is turning bad2. it makes a copy of its chromosome3. the rubbery cell membrane that surrounds the bacterial cell fluid
begins pinching inward around this chromosome copy. 4. the membrane of the mother cell surrounds and swallows up the
daughter cell.5. between these two membranes a thick wall forms made out of
stuff called peptidoglycan.6. a tough outer coating made up of a bunch of proteins forms
around all this, closing off the entire daughter cell.
For lecture only
Capsule Bacterial capsules outlined by India
ink viewed by light microscopy. A discrete layer of polysaccharide
surrounding the cells. Sometimes bacterial cells are
embedded more randomly in a polysaccharide matrix called a slime layer or biofilm.
Polysaccharide films that may inevitably be present on the surfaces of bacterial cells, but which cannot be detected visually, are called glycocalyx.
BC Yang
Capsule Stain of B. anthracis:
Capsule appears pink, bacterial cells purple
For lecture only
Capsule
Composed of poly-(D-glutamic acid), single antigenic type + proteins
Nontoxic, serves as an impedin in establishment of infection
Production enhanced in the presence of Na+-bicarbonate
may be plasmid-borne
prevents desiccation of the bacteria prevent phagocytosis by larger microorganisms and the
white blood cells of invaded host organisms help the bacteria adhere to the host substrate assist in warding off attacks by phages
BC YangFor lecture only
Pili (Fimbriae) singular pillus helical filaments, with ~1000 copies of
the major pilin, plus one or a few copies of ~5 minor pilins. The minor proteins provide binding specificity, membrane anchoring, and adapter functions.Mu, Egelman, Bullitt, 2002. J. Bact. 284(17):4868-4874Bullitt, & Makowski, 1995. Nature 373(6510):164-167
a) Adhesionb) In pathogenesisc) In environmentd) Sex pili
BC YangFor lecture only
Sex pili also called as type IV secretion system!
Flagellasingular flagellum
A tiny motor machine
BC YangFor lecture onlyShare similarity with type III secretion system
Each flagellum is a rigid structure The basal body causes rotation of the structure -- like a
propeller. The rate is about 12000 rpm Energy is derived from a proton gradient. Power has been
calculate to be about 10-15 amperes of current. Average velocities are in the range of 20 - 80 µM/s. About 1/2
foot per hour. A cheetah is 4 feet long and moves about 70
mph. 25 body lengths/second. A microbe that is 2 µM long,
moves 10 to 40 body lengths per second. (some bacteria are as
mobile as higher animals) Movement is a bias random walk during chemotaxis
BC Yang
Swing and tumble
For lecture only