20-40% of the volume of a G- cell lies between CM and OM; possible osmoregulation by membrane-derived oligosaccharides.

Binding Proteins: for amino acids, sugars, vitamins, ions

Degradative enzymes: phosphatases, proteases, endonucleases

Detoxifying enzymes: b-lactamase (penicillinase)

Biosynthesis: peptidoglycan biosynthesis

Energy production: cytochromes,

Environmental sensing: chemical sensors

Although G+ bacteria don't have OM, they still have "periplasmic space" of sorts enclosed by cross-linked peptidoglycan--more leaky, however.

S-LAYERS lie outside OM (G-) or PG (G+), and may be the only wall layer in some archaea. Role: Protection? Adherence?

Amorphous, loose layer. Can be polysaccharide (most common) or polypeptide. Prevents dehydration (general), can promote adhesion (Strep. mutans/teeth), prevent phagocytosis (Strep. pneumoniae, Neisseria meningitidis, B. anthracis, Haemophilis influenzae).

"Virulence factors"--may be conditionally produced; environmental sensing

Although glycoproteins very common in eucaryotes, rare in bacteria

Exception: Archaea have some glycosylated proteins (e.g., flagellins)

2-3 types of motility:

1. gliding motility mechanism is unknown

2. swimming requires flagellum/flagella

3. "other" (e.g., marine bacteria that swim but have no apparent flagella); some use "twitching" pili (Type IV pili)

Bacteria may have one flagellum or many flagella. Polar flagella--found at end of cell. Lophotrichous flagella: tufts. Peritrichous flagella: flagella everywhere.

Highly complex structure; requires approximately 40-50 gene products for its formation. Has 3 substructures

The FILAMENT is a long, extremely rigid left-handed helical structure that is 5-10 mm long and about 20 nm in diameter. The filament is usually composed of 1000's of copies of the protein FLAGELLIN. Flagellin spontaneously assembles at the end distal to the cell to form filaments.

The HOOK attaches the filament to the BASAL BODY. The hook is the universal joint, and is also largely made of a single protein. Diameter is about 25 nm in E. coli. Hook has defined length of about 55 nm

The BASAL BODY is a rotary motor that turns the flagella, therefore causing the cell to move. The basal bodies have rings for each layer of the cell wall, and they must act as both bushings and stators. G+ have only 2 rings. G- have 4 rings

The motor is made to turn by protonmotive force in most organisms (but by ion gradients, e.g. Ca++) in others. About 1000 protons are required for one complete turn of the motor.

"Swimming" only occurs when motors turn counterclockwise. CHEMOTAXIS will be discussed later

Archaea also have flagella, but their flagella are somewhat smaller, different from those of eubacteria (in fact, resemble class IV PILI). Right-handed helical structures contain multiple flagellins and probably assemble from cell surface outward (like pili).

For a review: Jarrell et al. 1996. The archael flagellum: a unique motility structure. J. Bacteriol. 178:5057-5064

PILI are organelles of attachment. Cells often express one or more types of pili (some times PHASE VARIATION occurs). E. coli has about 100-300 pili per cell. Diameter, about 2-8 nm with length 200 to 2000 nm (0.2-2.0 mm). Binding specificity is conferred by an "ADHESIN" at the tip. Targets are often sugars of polysaccharides or glycoproteins. Structures are typically composed of only a few proteins (FIMBRINS or PILINS). Assembly occurs from base of structure, the core diameters of pili are too small to allow subunits to pass through.

SEX PILI play a role in conjugation. Agrobacterium tumefaciens requires a pilus to deliver DNA to plant cells.

Pili are important in pathogenesis--allow pathogens to attach to specific cells. Neisseria gonorrhoeae

RIBOSOMES: site of translation of mRNA information into protein; require tRNAs to assist in this process. Several (a few to about 20) ribosomes associate with mRNA as soon as mRNA protrudes from RNA polymerase, forming POLYSOMES or POLYRIBOSOMES. Coupling of transcription and translation used in some regulation processes.

Small Subunit: 30 S ribosomal subunit.

Composed of 21 proteins and 1 molecule of 16 S rRNA (1542 nt in E. coli) "r" = ribosomal

Large Subunit: 50 S ribosomal subunit

Composed of 1 molecule of 5 S rRNA (120 nt) and 1 molecule of 23 S rRNA (2904 nt) and about 31-35 proteins.

Each protein is present at one copy per structure except for L7/L12, for which 4 copies total occur (L7 = L12 +N-terminal acetyl group).

This implies that all ribosomes are equivalent and that no "specialized" ribosomes occur in cells.

Ribosome structure has still not been solved at high resolution, although significant details have emerged from combination of many methods. See structures, p. 54 of textbook.

The DNA of the bacterial cell is contained in a compact structure, the NUCLEOID (= "nucleus-like"). Irregular appearance. E. coli seems to have 1-2 nucleoids/chromosomes per cell, but other cells can contain several nucleoids (as many as 10-20 copies per cell in some species)

DNA is highly condensed, and this requires counter ions due to charge on the phosphates. Mg++, polyamines (e.g., spermidine), and some proteins (HU proteins, IHF--all rich in lysines and arginines), and RNA polymerase help to condense the DNA structure.

Archaeal DNA is complexed with histones, as in eucaryotic cells. It is not known whether nucleosomes form in manner similar to eucaryotic DNA (DNA is wrapped around a histone octamer complex).

Isolated nucleoids seem to have a "core" with 50-100 radiating loops of DNA. TOPOISOMERASES wind and unwind the DNA to allow supercoiling to occur. Allows structure to be condensed about 500-fold.

1. GLYCOGEN. Bacterial starch = poly-glucose. Carbon storage (often made when nitrogen is limited)

2. POLY-b-HYDROXYBUTRYATE

(poly-b-hydroxyalkanes)

Alternative storage form for carbon

These compounds are poly-esters, hence plastics. Since made by microbes, they are BIODEGRADABLE

3. SULFUR GRANULES

Sulfur (Sulfide, thiosulfate) oxidizers frequently deposit elemental sulfur inside or outside cells.

4. POLYPHOSPHATE

Also known as Volutin or metachromatic granules

5. CARBOXYSOMES

Polyhedral bodies found in many different autotrophs. Site of CO2 fixation and the enzyme ribulose 1, 5-bisphosphate carboxylase/oxygenase (RuBisCO) that is the primary site of carbon fixation. Related structures may be found in bacteria that oxidize certain aldehydes

6. CYANOPHYCIN

Unique storage polymer for carbon and nitrogen found in cyanobacteria. The only known storage material for nitrogen (other than perhaps proteins in rare instances). Not synthesized on ribosomes

7. GAS VESICLES

Structures found in many aquatic microorganisms including archaea and eubacteria. Similar in all cases. Structures are cigar-shaped--very rigid. They are gas-filled and have a protein wall that allows gas but not water to pass. Hence, they create "empty space" in cells, and thereby buoyancy. High turgor pressures in cells can cause collapse of walls. Rate of synthesis and collapse can be used to position an organism in a water column.

8. MAGNETOSOMES

Crystalline particles of iron oxide (magnetite = Fe3O4). They have a protein coat that may play a role in precipitating Fe+3. Not used for iron storage, but used to orient cells in magnetic field.

9. CHLOROSOME, PHYCOBILISOME

CHLOROSOME are "sacs of Bchl" found in green sulfur bacteria--antenna for photosynthesis; PHYCOBILISOMEs are antenna structures found in cyanobacteria and are found on the surface of the INTRACYTOPLASMIC MEMBRANES (THYLAKOIDS).