Organization and Structure of Microorganisms

• Based on ribosomal RNA sequence comparsions (16S, 23S)

• 3 basic groups or domains established (domains are a higher order than kingdoms, ie are superkingdoms)

• The 3 domain = Bacteria, Archaea and Eucarya

• 3 domains are related to each other; progenote = hypothetical ancient universal ancestor of all cells.

• Natural relationships amongst cells established (phylogeny)

• Cell wall establishes the shape of a microbial cell but environmenta conditions can change it

• Shapes include:
• Spheres called cocci (greek = berry) can divide once in one axis to produce diplococci (Neisseria gonnorrhoeae, N. meningitidis), or more than once to produce a chain (Streptococcus pyogenes), divides regularly in two planes at right angles to produce a regular cuboidal packet of cells (xxx) or in two planes at different angles to produce a cluster of cells (Staphyloccus aureus)
• Cylinders called rods or bacilli (Latin bacillus = walking stick)
• Spiral or spirilli (Greek spirillum = little coil)

• Shape offers an advantage to the cell:
• Cocci: more ressistant to drying than rods
• Rods: More surface area  & easily takes in dilute nutrients from the environment
• Spiral: Corkscrew motion & therefore less ressistant to movement
• Square: Assists in dealing with extreme salinities

• Nutrients and wastes are transported in and out the cell via the cytoplasmic membrane.

• The rate of transport determines the metabolic rates and therefore the growth rates of microbial cells

• The smaller the size, the larger the surface area of the cytoplasmic membrane to volume and therefore the faster is it's potential growth rate. This can be seen as follows:

This section deals with the structure and functions of cells. Cells are of three types as described above (Bacteria, Archaea & Eucarya) and the description below provides similarities and differences amongst these cell types.
 
Diagramatic representation of cells

1. Bacterial Cell Walls:

• All the members of domain Bacteria, with the exception of the genera Mycoplasma, Ureaplasma, Spiroplasma, and Anaeroplasma contain cell walls

• Cell walls are chemically peptidoglycans ie peptides (short amino acids chains) and glycans (sugars); peptidoglycans  are a.k.a. mureins, mucopeptide.
• Glycans:
• are modified sugars viz, N-acetyl muramic acid (NAM or M) & N-acetly glucose amine (NAG or G)
• M and G are linked to each other by a beta 1, 4 glycosidic bond &  alternate to form the wall backbone.
• Lysozyme (an enzyme produced by organisms that consume bacteria, and normal body secretions such as tears, saliva, & egg white = protect against would-be pathogenic bacteria) digests beta 1,4 glycosidic bonds.
• Lysozyme lyses growing or non growing cells but cell wall-less microbes are not affected
• High osmotic pressure in high solute concentrations prevents lysis of Gram +ve & Gram -ve cells when treated with  lysozyme:
• spheroplasts  = part of cell wall  removed (Gram -ve)
• protoplasts = complete removal of cell wall (easier for Gram +ve)

• Peptides:
• Short peptides (4 amino acids, tetrapeptides) attached to M.
• Some of the amino acids are only found in cell walls & not in other cellular proteins (D- amino acids, eg D-alanine & diaminopimelic acid, DAP)
• Tetrapeptides chains are cross linked (interlinked) by a peptide bridge (the carboxyl group of one tetrapeptide with an amino group of an adjacent (direct interbridge) or a different tetrapeptide chain (indirect interbridge).
• Transpeptidase enzyme builds peptide bridges in actively dividing cells; penicillin binds to it stoping cell wall synthesis. Autolysins restructure and reshape cell walls by breaking specific bonds in the peptidoglycan in actively growing cells. Cell wall synthesis stops but cell degrading enzymes still function resulting in weakened cell walss and ultimately death.

• Glycans and peptides therefore forms a single, large and strong cross-linked molecule in a form of a multilayered sheet, (sacculus, Latin = little sac) that surrounds the entire bacterial cell.

 
2. Archaeal Cell Walls:

• Archaeal cells have more variations in their cell wall chemistries, and some do not contain cell walls (eg Thermoplasma)

• Methanobacterium sp. contain glycans (sugars) and peptides in their cell walls:
• Glycans:
• are modified sugars viz, N-acetyl talosaminouronic acid (NAT or T) & N-acetly glucose amine (NAG or G)
• T and G are linked to each other by a beta 1, 3 glycosidic bond &  alternate to form the cell wall backbone.
• Lysozyme (an enzyme produced by organisms that consume bacteria, and normal body secretions such as tears, saliva, & egg white = protect against would-be pathogenic bacteria) cannot digest beta 1,3 glycosidic bonds.
 
• Peptides:
• Short peptides attached to T.
• The amino acids are only of the L-type
• Penicillin is ineffective in inhibiting the cell wall peptide bridge formation.

• Methanosarcina sp. cell walls contain non-sulfated polysaccharides

• Halococcus sp. contain sulfated polysaccharides similar to Methanosarcina sp.

• Halobacterium sp. contain negatively charged acidic amino acids in their cell walls which counteract the positive charges of the high Na⁺ environment. Therefore, cells lyse in NACl concentrations below 15%.

• Methanomicrobium sp. & Methanococcus sp. cell walls are exclusively made up of proteins subunits.

3. Eucaryal Cell Walls:

• Cell walls of algae have a variety of different cell wall types and include cellulose, calcium carbonate, silcone dioxide, proteins and even polysaccharides.

• The cell walls of fungi are made up of chitin (a nitrogen-containing polysaccharide) and is similar to that found in the exoskeletons of arthropods & crabs

• Protozoa do not have a true cell wall. In some species, silicon dioxide, calcium carbonate or strontium sulfate are found but do not provide the cell wall with a protective function.

4. Glycocalayx, Capsules, Slimer Layers & S layers:

•  Various external structures which have different functions surround the bacterial cell wall, and are collectively called glycocalyx.

• Glycocalyx varies in different species:
• Capsules:
• Are thick & rigid structures which exclude stain.
• Adhere externally to the to cell walls
• Negative stain allows capsules to be observed.
• Chemically polysaccharides.  Found in pneumonia causing pathogens such as Streptococcus pneumoniae, Haemophilus influenzae & Klebsiella pneomoniae.
• Chemically D-glutamic acid found in some Bacillus sp.
• Capsulated variants of a species are pathogenic whereas non-capsulated variants of the same species are non-pathogenic. Capsules protect against phagocytosis by human white blood cells.
• Slime layers:
• Similar in composition to capsules but are not as tightly bound to the cell wall.
• Protects cells against dehydration and a loss of nutrients.
• S layer:
• Some bacteria have a crystalline protein layer called a S layer.
• Found outside the cell walls of some species of Gram-negative, Gram-positive Bacteria, and outside the cell membranes of some Archaea.
• Function is unknown.
 

• Thickness 4-5nm

• Regulates flow of molecules in and out of the cell but is a differentially permeable barrier- movement across the membrane is selectively restricted (structure & chemistry is key to this)

• Small, neutrally charged molecules (H₂O, O₂ & CO₂) easily transportable but large molecules & ions (glucose) or small  charged atoms (protons, H⁺) require specific transport systems.

• Provides increased surface area to volume & is very important to small cells

• Bilayered structural backbone are the phospholipids (bacteria & eucaryotes only); forms a separation barrier with water inside and outside the cell

• "Fluid mosaic model": Proteins are integrated into the lipid layer and both "float" laterally in the membrane ie are in dynamic rather than static state (lipids float more than proteins)
•  Peripheral proteins: confined to the membrane surface
• Integral proteins: partially / completely buried & may span the entire membrane

• Distribution & properties of proteins on each side of the layer are different & therefore the functions of the 2 layers are different

• The structure and chemical properties of archaeal, bacterial and eucaryotic membranes are "phylogenetically" distinct

• Characteristics of Bacterial Eucaryotic Archaeal cytoplasmic membranes

1. Bacterial cytoplasmic membranes:

(a) Phospholipids: (structure, functions & utility)

• Made of phospholipids - a phosphate group joined to 2 fatty acids by glycerol (glycerol diester); oleate, stearate

The phosphate group is -vely charged & is therefore hydrophilic ("water loving")- exposed to cell wall & cytoplasm
The fatty acid group is nonpolar & therefore hydrophobic ("afraid of water")- exposed within the internal membrane matrix
 

• Electron micrographs of thin sections of bacteria cells show a pair of electron dense dark railroad track-like appearance (hydrophilic portion) & electron light middle layer (hydrophobic)

• Form a bilayer due to hydrophobic / hydrophilic interactions (spontaneous aggregation)- contributes to flow of molecules.

• Phospholipid composition varies with species & environmental conditions
• Psychrophiles: high proportion of unsaturated fatty acids enhance membrane fluidity (saturated fatty acids pack together more tightly & produce a rigid less-fluid membrane)
• Bacteria can be identified on phospholipid composition (computerized databanks available) but cells have to be grown under standard conditions (Why?)

• Are in dynamic state and distribution is according to the fluid mosaic model

• Sterols not present but are present in cell wall-less bacteria (Mycoplasma, Ureaplasma, Spiroplasma, Anaeroplasma)- required for growth, provide stability eg sterols.  Poylene antibiotics (eg nystatin, candicidin) inhibit growth by interacting with sterols & destabilising eucaryotic & cell wall-less bacterial membranes (but do not inhibit growth of cell wall containing bacteria)

2. Archaeal cytoplasmic membranes:

• Structure fundamentally different to bacterial & eucaryotic membranes

• Glycerol molecules may be linked:
• to a phosphate group (similar to bacteria & eucaryotes) and / or
• to a sulfate and carbohydrates (unlike bacteria & eucaryotes) & therefore phospholipids are not the structural lipids

• Lipids are hydrocarbons (isoprenoid hydrocarbons) not fatty acids, are branched (straight chain in bacteria & eucaryotes) and linked  to glycerol by ether bonds (ester linked in bacterial & eucaryotes).

• Lipids are diverse in structure
• Glycerol diether (Glycerol + C₂₀ hydrocarbons)- Bilayered membrane
• Glycerl tetraether (Glycerol + C₄₀ hydrocarbons)- Monolayered membrane
• Mixture of di- & tetra- Mono /Bi layered membrane
• Cyclic tetraethers (Glycerol + > C₄₀)- maintain the 4-5nm membrane thickness

• Diversity of membranes is related to the diverse habitats that archaea live in
• Sulfolobus (90^oC, pH 2)- branched chain C₄₀ hydrocarbons. Branched chains increase membrane fluidity (unbranched & saturated fatty acids limit sliding of fatty acid molecules past one another)- required for growth at high temperatures (upto 110^oC, hyperthermophies)
• Halobacterium (saturated salts)-
• Thermoplasma- high temperature, cell wall-less archaea

• Phospholipids similar to bacterial membranes but terols make upto 25% of the lipids
• cholestrol in humans
• ergosterol in fungi

• Membranes must selectively regulate transport of materials and waste ie semipermeable & several mechanisms are available for this:
• Pass directly enter thro' the lipid layer or via proteins
• Altered / modified as it passes thro'
• Process requires cellular energy
• Solutes are concentrated against a gradient
 

(a) Diffusion

• Unassisted movement of molecules from a higher concentration to lower concentration (concentration gradient) until equilibrium is reached is called passive diffusion.

• Rate of diffusion depends on membrane permiability & solute concentrations

• Some solutes after moving into the cell binds with some other proteins or are metabolically transformed. Therefore concentration is not built up in the cell & the diffusion process continues at a faster rate

• Passive diffusion is slow eg glucose and tryptophan have diffusion rates of 1/10,000 that of water, & not enough for cellular growth & reproduction

• Process by which water croses the membrane in response to concentration gradient of the solute 30 minutes at 70^o C

• Water moves from a region of low solute concentration to high solute concentration
• isotonic- solute conc. outside the cell = solute conc. inside the cell
• hypertonic- solute conc. is higher than that inside the cell; water flows out causing the cell to shrink, plasmolysis
• hypotonic- reverse of hypertonic; water will flow into the cell & the cell will burst

• Usually water moves into the cell as cytoplasm has solutes resulting in increased pressure on the membrane- osmotic pressure. Cells can lyse due to osmotic shock but have developed strategies to protect against this (see shock-sensitive proteins later)

• Enhanced rate of diffusion found mainly in eucaryotic cells but rarely in bacteria & archaea (glycerol is the only known substrate that undergoes facilitated diffusion in some bacteria)

• Facilitator proteins (membrane proteins) selective increase the permeability of the membrane for certain solutes

•  Facilitator proteins are very specific & act as carriers ie solutes bind to the facilitator protein changing its 3D properties. This change in shape allows the solute to be carried across the membrane

(a) Active Transport

• Active transport requires energy but the molecule is not modified during transport

• Transport occurs against concentration gradients

• Permeases are very specific membrane protein transport carriers
• Uniporters- carry one substance at a time
• Cotransporters- carry more than one type of substance
• Symporter- Two substances carried in the same direction simultaneously [(eg lactose & proton (H⁺)]
• Antiporter- Substances are transported across the membrane in opposite directions (eg Na⁺ are pumped outside the cell at the same time H⁺ are transported inside the cell)

• Energy for active transport in bacteria (oxidative phosphorylation) in archaea, algae, mitochondria & chloroplasts generally comes from PMF. PMF force is essential

• Various metabolic activities produce protons (H⁺) and these are translocated outside the cell. Higher concentrations & an  increase in  positive charge outside the cell favours movement of protons back into the cell but cannot do so on their own. Uncharged molecules (eg amino acids & sugars) are usually transported into the cell with protons

• The various means by which PMF is produced will be discussed later

•  A gradient between Na⁺ & K⁺ similar to protonmotive force & known as sodium-potasium pump

• Found in many eucaryotes

• Three Na⁺ are pumped out of the cell and two K⁺ are pumped into the cell by Na⁺-K⁺ ATPase enzyme; ATP is expanded

• Unequal distribution of positive ion with a higher Na⁺ conc. outside the cells and a higher conc. of K⁺ inside the cells; leads to a powerful electrochemical gradient used for active transport (eg symport protein binds both Na⁺ and glucose for transport therebye lowering Na⁺ conc gradient across the membrane)

• Transported substance is chemically altered during passage thro' the membrane by the addition of phophate

• Carbohydrates, fatty acids, some nucleic acid building blocks.

• In E. coli, glucose outside the cell is phosphorylated during transport (G6-P) into the cell
• Metabolism almost instantaneous once inside (couples energy resources efficiently thro transport & initiation of energy-generating metabolism
• concentration gradient of glucose is prevented (not in the same chemical state)
 
• Prokaryotic specific; in anaerobes, facultative anaerobes but not in aerobes (active transport occurs)

• Mechanism of PEP:PTS
• Phosphate group is transferred from PEP to a LMW histidine containg protein (HPr) found in the cytoplasm mediated by Enzyme I.
• The phosphorylated-HPr then transfers the phosphate group to Enzyme III
• Enzyme III  transfers the phosphate to Enzyme II.
• Enzyme II is a phosphoprotein (phosphate group is attached to histidine or cysteine & is transferred to the substrate being transported thro' the membrane)
• Glucose & fructose transported by this means.
• In manitol, enzyme II is phosphorylated directly by HPr without the intervening Enzyme III
• Enzyme I & HPr are substrate nonspecific & mutants lacking the genes pts1 & ptsH respectively lead to general failure of all substrate transport
• Enzymes II & III are substrate specific eg Enzyme II^glu transports glucose, glucosamine & 2-deoxyglucose whereas Enzyme II^fru transports fructose. Mutants lead to failure of transport of the particular substrate only

•  Specialized transport system associated with the outer membrane of Gram negative bacteria only

• Periplasmic space(periplasm, periplasmic gel) is the space between the outer membrane & the cytoplasmic membrane

• There is interplay between porins, binding proteins, permeases & transport proteins, eg maltose transport in E. coli
• maltose is transported into the periplasmic space by a porin (LamB) found in the outer membrane
• Binds to a soluble periplasmic binding protein& is shuttled to another binding protein
• At the CM an additional complex of proteins are found
• MalF and MalG act as permeases to transport maltose thro the CM
• MalK is involved in obtaining energy from ATP for the transport process

• Binding protein transport is also called shock-sensitive transport (cells that are osmotically shocked loose the transport proteins of the periplasm)

•  A transport process in which a substance is engulfed by the CM to form a vesicle (transport is not thro' but is around the CM)

• Cytosis requires energy
• Endocytosis- movement into the cell
• Exocytosic- movement out of the cell
• Phagocytosis- engulfing by a cell of a smaller cell or a particle (protozoa, Amoeba)
• Pinocytosis-  cell engulfs liquid
• Receptor-mediated endocytosis- receptor binds to a substance and assist in transport (viruses and host cells)
 
 
 

• ATP generation & utilization is a central metabolic activity.

• The location & structures involved in cellular-energy generating reactions will be discussed here
• Some reactions occur in the cytoplasm
• Some cell membrane structures are a key to generate cellular energy

• Two mechanisms for generating cellular energy
• Substrate level phosphorylation:
• Direct chemical coupling between ATP generating & ATP requiring reactions
• No specialized membrane structures necessary
• Occurs in cytoplasm
• Occurs in bacterial, archaeal & eucaryal cells (also mitochondria & chloroplasts)
• Chemiosmosis:
• Generates ATP using energy of a proton gradient across a membrane (proton motive force): Various metabolic activities produce protons (H⁺) and these are translocated outside the cell. Higher concentrations & an  increase in  positive charge outside the cell favours movement of protons back into the cell but they can get into the cell by cotransport (see above) or thro the pores of special proteins, ATPase
• Requires membranes-with membrane bound ATPases
• Occurs in two distinct processes
• generation of a proton motive force across a gradient
• use of energy stored in the gradient to drive the phosphorylation of ADP by ATPase
• Occurs
• at the cytoplasmic membranes of archaeal & bacterial cells
• in some specialized bacterial cells at internal membranes (extensive invaginations of the CM of nitrifying bacteria: oxidation of inorganic nitrogen compounds & ATP generation; chromatophores in purple sulfur are simple extensions, cylindrical vesicles in green bacteria & multilayered membrane thylakoids in cyanobacteria
• at the cytoplasmic membranes of mitochondria (inner but not the outer membrane extremely convoluted protruding into the cytoplasm (cristae) contains high proportions of energy-transferring proteins present-of Eucarya (in "primitive" anaerobic protozoa Giardia do not have mitochondria but contain hydrosomes where ATP is generated)
• in chloroplasts of alga & plants; inner but not the outer membrane convoluted (stroma, fixation of CO₂); proton gradient forms across internal membranes called thylakoids drives chemiosmosis (flow of protons inwards but in mitochondria is outwards)
 

• Historical Developement & Importance
• 100's of species mainly of the genera Bacillus (aerobic rods, facultative anaerobes), and Clostridium (anaerobic rods); Few others include Sporosarcina (aerobic cocci), Desulfotomaculum (anaerobic rods, sulfate-reducers)
• Food industries (canning, milk etc) heat treat products to reduce microbial spoilage & kill pathogens; spore-formers are a problem (swelling of tins; putrification of meat etc)
• Mainly found in soils --> vegetables --> meat where spores germinate to produce toxins (eg veg / meat salad stored improperly prior to use; wooden choping boards prefered over synthetic)
• Mainly found in soils --> infect wounds (problem with farm associated workers)
• Some strains were being developed for biological warfare eg B. anthracis (anthrax)
• Some strains produce important biopesticides (biotechnology) eg B. thuringiensis var. israelensis produces toxic proteins against mosquito & blackfly larvae. Commercial variants  available which produce toxins towards slightly different insect pests eg Thuricide, Teknar, M-one.
• Spore which can germinate have been found from structures 7200 year old temples have been found and recently from GI tract of a bee preserved in amber (1 million years old)

• Distribution

• Size
• Larger (distends the cell) or smaller than the cell

• Shape
• Cylindrical
• Ellipsoidal
• Spherical

• Location
• Central
• Terminal
• Sub-terminal

• Cells with endospores can be identified by spore-staining
• B. megaterium,an aerobe: Small cylindrical sub-terminal spores
• C. tetani, an anaerobe: Large (distend) spherical terminal spores
 
• Heat ressistance

• Spore structure
• Spores are formed during unfavourable growth conditions & germinate under favourable conditions
• The spore can be differentiated into 4 distinct parts:
• Core: Nucleic acids, ribosome, low levels of enzyme activity, Calcium dipicolonic acid (CDPA) & low water content. Low level of metabolic activity
• Two wall like layers:
• Cortex: Surrounds the core, mainly electron light peptidoglycan
• Coat: Surrounds the cortex, mainly protein
• Exosporium: The outer most thin layer

• Mechanism of heat ressistance
• Physical (sporecoat): Ressistance to staining demonstrates imperability & therefore ressistant to dehydration & effects of toxins (multilayered thick peptidoglycan)
• Chemical (core): Low water content (15% instead of 80% found in cells) makes prteins & nucleic acids more ressistant. CDPA complexes with proteins & other labile components & makes them more ressistant. Medium lacking calcium or mutant strains that do not form CPDA produce less "tolerant" spores.
 

• Ressistant to dehydration but not to heat and hence unlike spores

• Deposition of layers & layers of cell wall around the cell rather than within the cell as in case of spores

• Azotobacter (free living nitrogen fixing bacterium found in soil) and Myxbacteria

• Involved in nitrogen fixation and protection

• Usually a single circular chromosome (Streptomyces & Borrelia = linear, Rhodobacter sphaeroides = 2 separate chromosomes)

• "Naked DNA" - not membrane bound (nucleoid region)

• Negatively supercoiled (highly twisted)- can expand to 1mm in length uncoiled (length of a "typical" bacterium is a few micrometers

• not associated with histone proteins (histones responsible for eucaryotic DNA coiling)  but histone-like proteins found

• Genome size extremely heterogenous, determined in nucleotide base pairs (bp)

Microbe	Characteristics	Size (Mb)	Sequence information
Mycoplasma genitalium	No cell wall, bact	0.58
Haemophilus influenzae	bact pathogen	1.83
Helicobacter pylori	bact pathogen
Neisseria meningitidis	bact pathogen
Escherichia coli	GI bact	4.4
Thermotoga maritima	bact thermo
Archaeoglobus fulgidus	archaea thermo
Pyrodictium occultum	archaea thermo
Methanococcus jannaschii	archaea therm

 
• G+C content  between 28% to 72%

• Cell division (binary fission) & DNA duplication are synchronised. DNA duplication is slower than cell division & therefore new rounds of DNA synthesis are initiated by the cell even though the previous copy has not fully replicated. A cell can carry one full copy & several partial copies

•  small, circular, self replicating extrachromosomal genetic elements- >= 1

• the genetic information supplements the chromosomal genetic information
• antibiotic ressistance
• tolerance to toxic metals
• production of toxins
• mating capabilities

• genetic information is 1 - 5% of chromosomal DNA information but means 0% or 100% survival eg antibiotic ressistance

• classfied on the basis of its function
• "mating" plasmids - F (fertility) factor
• antibiotic, metal ressistance- R (ressistance) factor

• benefits & hazards
• multiple drug ressistant pathogens
• genetic engineering- cloning & expression of useful substances

•  linear chromosomes associated with chromatins; chromatins are histone proteins (basic proteins) around which DNA coils (~ 200 nucleotides/histone) to form nucleosomes- "beads on a string" under EM

• chromosomes are located in the nucleus
• nucleus is separated from the cytoplasm by pore containing nuclear membrane (double layered bilayered membrane)
• more processing of the DNA is needed before it can be expressed & hence this type of separation is necessary

• usually greater than 1 different sized chromosomes present

Eucaryotic cell	Numbers	Size range (Mb)

 

• Dinoflagellate algae is an evolutionary link between eucaryotes and bacteria-
• DNA inside nucleus (similar to eucaryotes)
• not histone associated ie not coiled like eucaryotic chromosomes
• DNA arangement is similar to that of bacterial DNA (nucleoid region)

• DNA -------> RNA (tRNA, mRNA, rRNA)-------->proteins

• ~10,000 ribosomes in archaea & bacteria depending on growth rates but many more in eucarya

• Measured in Svedgurg (S) units: rate of sedimentation in an ultracentrifuge dependent on shape & size.

• Bacteria & Archaea:
• 70S (30S = 21 proteins, 16SrRNA [~1542 nucleotides] + 50S = 34 proteins, 23S rRNA [2900 nucleotides, 5S [120 nucleotides]) -- Phylogeny.
• Similar 70S but differences exist in protein composition
• archaea are not sensitive to antibiotics that inhibit bacterial protein synthesis tetracycline, erythromycin, chloramphenicol
• diptheria toxin & anisomycin affects ribosomes of archaea but not bacterial

• Eucarya:
• 80S (40S = 18SrRNA, 60S = 25 to 28S rRNA, 5.8S rRNA)
• synthesised in the nucleolus & transported via nuclear pores into cytoplasm
• Primitive protozoa Giardia contains 70S
• mitochondria & chloroplast contain 70S; rRNA sequence shows similarity to noncultured archaea & Rickettsia (proteobacteria) endosymbiotic theory.

• Differences in 70S & 80S can be targeted for treatment of animal / plant diseases
• Streptomycin & Erythromycin bind & alter 70S shape of bacteria not eucaryotes

• Bacteria store chemicals under certain conditions. eg, increased carbon availability but not inadequate nitrogen-containing compounds for protein synthesis available.

• Not separated by membranes & display differential solubility
• Nutrient reserves synthesised by the cell: poly-beta-hydroxybutyrate (PHB)
• Energy reserves: inorganic polyphosphates (volutin, metachromatic granules) for ATP synthesis; viewable after staining by light microscopy
• Metabolic deposits: Sulfur deposited as a result of metabolism (photosynthetic bacteria)

•  Endoplasmic reticulum
• Golgi apparatus
• Lysosomes
• Microbodies
• Vacuoles
• Cytoskeletal network

• Bind cells togethr forming multicellular aggregates

• In some cases the bacterial cells adhere to solid surfaces using these structures.
• Some pathogenic bacteria adhere to animal tissues
• Some aquatic bacteria adhere to rocks
• Some are involved in plaque formation leading to dentall caries

• Not all bacteria posses fimbrae -- it is an inherited trait

• Arise from the cytoplasmic membrane or just below the membrane

• Can be mistaken for flagella but are not involved in motility

• Much shorter and more numerous than flagella

• Adhesion functions which enables cells to form a pellicle on liquid surfaces

• Similar to fimbrae but longer and fewer; sometimes only one per cell

• Three functional types of bacterial pili:
• Act as receptors sites for some attachment of some phages ie phage infection
• Act as sex pilus for bacterial conjugation processes (F aka Fertility pili of E. coli)
• Attachment for pathogenic bacteria to human tissues (Neisseria gonorrhoeae)