Mikro 02 2010

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PowerPoint ® Lecture Slide Presentation

B.E Pruitt & Jane J. Stein

Chapter 02The Prokaryote: Bacteria

REFERENCES and FIGURES

Tortora GJ, Funke BR, Case CL, 2007, Microbiologyan Introduction , 9 th edition, Benjamin Cummings, SanFrancisco, CA 94111, USA

Madigan MT, Martinko JM, 2006, Brock Biology ofMicroorganisms , 11 th edition, Pearson Education Inc.,USA

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Prokaryotic Cells

• Comparing Prokaryotic and Eukaryotic Cells

• Prokaryote comes from the Greek words for prenucleus.

• Eukaryote comes from the Greek words for true nucleus.

Comparison between prokaryotes and eukaryotes

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• Average size: 0.2-2.0 µm diameter, 2-8 µm in length

• Basic shapes:

Size, shape and arrangements

• Unusual shapes

• Star-shaped ( Stella )

• Square (Halophilic archaea, Haloarcula )

• Most bacteria are monomorphic

• A few are pleomorphic ( Rhizobium , Corynebacterium )

Size, shape and arrangements

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Structure of bacterial cell

• Composed of polysaccharide, polypeptides, or both

• A capsule is neatly organized

• A slime layer is unorganized & loose

• Capsules prevent phagocytosis ( B. anthracis )

• EPS allows cell to attach and colonize ( Klebsiella );biofilm formation

• Barrier for biocides, disinfectants, AB

• Source of nutrition ( S. mutans )

• Protects against dehydration

• Inhibit the movement of nutrients

Glycocalyx

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• Semirigid, helical structure

• 3 basic parts• Gram (-) 2 pair of rings

• Gram (+) inner pair

• Motility

• Taxis (attractant, repellent)

• Chemotaxis(O 2, ribose, galactose)

• Phototaxis

• Receptor in various location• Flagella proteins are H

antigens

Flagella

Flagella arrangement

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• Endoflagella

• In spirochetes(Treponema pallidum )

• Anchored at one end of acell

• Rotation of the filamentscause cell to move

Axial filaments

Axial filamentsEndoflagella: bundle of fibrils that ariseat the ends of the cell beneath an outer sheath and spiral around the cell

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• Fimbriae allowattachment (biofilm)

• Few or severalhundred per cell

• N. gonorrhoeae

• Pili are used totransfer DNA fromone cell to another

• One or two per cell

• Conjugation pili • Mediated by plasmids

Fimbriae and Pili

• Complex, semirigid structure

• Prevents osmotic lysis (water)

• Maintain shape of the cell and serves as a pointanchorage for flagella

• Contributes in some species to cause disease

• Made of peptidoglycan (in bacteria); site action of AB

• Compared to eukaryote’s cell wall, differ inchemically, are simpler and structure and less rigid

Cell wall

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• Polymer of disaccharideN-acetylglucosamine (NAG) & N-acetylmuramic acid(NAM); murus means wall

• Linked in row of 10 to 65 sugars to form “backbone”

• Linked by polypeptides

• tetrapeptides side chain (4 amino acids) and peptidescross-bridge

Peptidoglycan ( murein )

Cell wall

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Gram-positive cell wall

Gram-negative cell wall

Gram (+) and (-) cell wall


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• Forming thick and rigid structure

• Teichoic acids : negative charge, regulate themovement of cations into and out of the cell

• Assume in cell growth, preventing excessive wallbreakdown and possible cell lysis

• Antigenic specificity, identification of bacteria

• Resistance to physical disruption

• In acid-fast cells , contains mycolic acid (60%);

thin layer peptidoglycan; held together bypolysaccharide

• Acid-fast cells: Mycobacterium and Nocardia


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• Periplasm : contains hydrolytic enzymes, bindingproteins, chemoreceptors

• Outer membranes : strong negative charge, helpsevading phagocytosis and action of complement

• Protection to ABs, digestive enzymes (lysozyms,detergents, heavy metals, bile salts, and certain dyes)

• Porins (protein): form channels (hydrophilic low-MW)through membrane, e.g. nucleotides, disaccharides,peptides, amino acids, vitamin B 12 and iron

• O polysaccharides : antigens, determine the species

• Lipid A : endotoxins

• Penicillin vs gram negative: outer membranes, barrier

Characteristics of Gram (+) and (-)

LowHighResistance to Drying

LowHighResistance to Sodium Azide

LowHighSusceptibility to Anionic Detergents

LowHighInhibition of Basic Dyes

HighLowSusceptibility to Streptomycin,Chloramphenicol and Tetracycline

LowHighSusceptibility to Penicillin And Sulfonamide

Low (requires pretreatment todestabilize outer membrane)

HighCell Wall Disruption by Lysozyme

LowHighResistance to Physical Disruption

Primarily endotoxinsPrimarily exotoxinsToxins Produced

4 rings in basal body2 rings in basal bodyFlagellar Structure

High (due to presence of outermembrane)

Low (acid-fast bacteria havelipids linked to peptidoglycan)

Lipid and Lipoprotein Content

HighVirtually noneLipopolysaccharide (LPS) Content

PresentAbsentOuter Membrane

PresentAbsentPeriplasmic Space

AbsentPresent in manyTeichoic Acid

Thin (single-layered)Thick (multilayered)Peptidoglycan Layer

Can be decolorized to acceptcounterstain (safranin) andstain pink

Retain crystal violet dye andstain dark violet or purple

Gram Reaction

GRAM NEGATIVE GRAM POSITIVE CHARACTERISTIC

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• Genus Mycoplasmas• Lack or very little material of cell walls

• Smallest bacteria that can grow and reproduceoutside living host cells

• Pass through 0,2 µ m membrane filters

• Sterols in plasma membrane: help protect from lysis

• Starting materials requiring special attention

• Cell cultures for the production of veterinaryvaccines

• Cell substrates for the production of vaccines for human use

Atypical cell walls

Plasma membrane

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• Passive process : movement of substance from ↑ [ ]→ ↓ [ ], move with the gradient [ ], without ATP

• Simple diffusion : Movement of a solute from ↑ [ ]→ ↓ [ ], equilibrium, small molecules (O 2, CO 2)

• Facilitative diffusion : Solute combines with atransporter protein ( permease ) in the membrane

• Osmosis : movement of water across a selectivelypermeable membrane from ↑ [ ] → ↓ [ ], isotonichypotonic, hypertonic solution

• Most bacteria live in hypotonic solution andswelling contained by the cell wall

• Most bacteria produce enzymes that can break downlarge molecules: extracellular enzymes , released bybacteria into the surrounding medium

Movement across membranes


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• Active process : movement of substance from ↓ [ ]→ ↑ [ ], move against the gradient [ ], with ATP

• Active transport of substances requires atransporter protein and ATP.

• Group translocation of substances requires atransporter protein and phosphoenolpyruvic acid

(PEP)• Substance is altered during transport across the

membrane

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• Cytoplasm is the substance inside the plasmamembrane

• Contains 80% water, proteins, carbohydrates, lipid,inorganic ions, low-MW compounds

• Major structures: nuclear area (DNA), ribosomes,inclusions

• Protein filaments are most likely responsible for the rodand helical shapes of bacteria

• Prokaryotes cytoplasm lack of cytoskeleton andcytoplasmic streaming

Cytoplasm

• Bacterial chromosomes : single long, continuous,circularly, double-stranded DNA

• Bacterial chromosomes aggregate to form a visiblemass called nucleoid

• Genetic information for cell’s structure and function

• Not surrounded by nuclear envelope, lack histones

• The chromosomes is attached to plasma membrane• Protein in plasma membrane are believed to be

responsible for replication of the DNA and segregationof the new chromosomes daughter cells during division

Nuclear area (nucleoid)

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• Plasmids : circular, double-stranded DNA molecules• Extrachromosomal genetic elements

• Contain 5-100 genes and not crucial for its life

• Plasmids can be gained or lost without harming the cell

• Carry genes for antibiotic resistance, tolerance to toxicmetals, the production of toxins and synthesis of enzymes

• Plasmids responsible for conjugation and transmissiblebetween cells during conjugation

• Plasmids can be transferred between species or genus• Plasmids DNA is used for gene manipulation

Nuclear area (plasmids)

Plasmids (R factor)• RTF: plasmid replication and transfer by conjugation

• R determinant: production of enzymes (exoenzymes,exotoxins), adhesins, inactivate drugs

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Ribosomes

• Synthesis protein

• Two subunits: protein (40%) and rRNA (60%)

• Smaller and less dense compared to eukaryotes cells

• 70S: 30S (1 mol. rRNA) and 50S (2 mol. rRNA)

• Medically targeted: aminoglycosides (30S), erythromycin& chloramphenicol (50S)

• Reserve deposit

• Evidence suggests that macromolecule concentratedin inclusions avoid the increase in osmotic pressurethat would result if the molecule were dispersed in thecytoplasm

• Serve as a basis of identification

• Metachromatic granules (volutin ): inorganic phosphate

(polyphosphate), synthesis ATP• Polysaccharide granules : glycogen and starch

• Lipid inclusions : polymer poly- β-hydroxybutyric acid

• Sulfur granules : oxidizing sulfur and sulfur-containingcompound

Inclusions

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• Carboxysomes : contain enzymes ribulose 1,5-diphosphate carboxylase for CO 2 fixation

• Gas vacuoles : gas vesicle , hollow cylinders covered byprotein, maintain buoyancy so the cells can remain atthe depth in the water appropriate for them to receivesufficient amount of O 2, light and nutrients

• Magnetosomes : Fe 3O 4, move downward until reach asuitable attachment site, may protect the cell againstH2O 2 accumulation

Inclusions

• Differentiated cells, highly resistant

• Ideal structure for dispersal (wind, water & animal gut)

• 20 genera (Bacillus, Clostridium, Sporosarcina andHeliobacterium)

• Dipicolinic acid (DPA), located in the core

• Rich of Ca 2+ , combined with DPA, 10% of dry weight

• Reduce water availability, helping to dehydrate

• The complex intercalates (insert between bases) inDNA → stabilize it to heat denaturation

• SASPs ( s mall a cid -s oluble p roteins )

• Bind tightly to DNA in the core and protect it

• Carbon and energy source during germination

Endospores

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Endospores

• Exosporium : protein

• Spore coat : spore-specific protein

• Cortex : loosely cross-linked peptidoglycan

• Core or spore protoplast :core wall, cytoplasmicmembrane, cytoplasm,nucleoid, ribosomes,other cellular essentials

Endospores

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Endospores

Bacillus subtilis , 8 hours for the sporulation process

• Activation

• Heating several minutes at sublethal temperature

• Germination

• Placed in the specific nutrients (AAs, alanine)

• Rapid process (several minutes)

• Loss microscopic refractility, loss of resistance toheat and chemical, loss of Ca 2+-DPA and cortex,SASPs are degraded

• Outgrowth

• Visible swelling due to water uptake

• Synthesis of new RNA, proteins and DNA

Endospores germination

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