bacterial form and function microbiology- ch. 4 pp 87-101
TRANSCRIPT
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Bacterial Form and Function
• Microbiology- Ch. 4 pp 87-101
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Structure of a Prokaryotic Cell
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Prokaryote Structures:
1. Appendages- flagella, pili, fimbrae
2. Cell envelope- glycocalyx, cell wall , cell membrane
3. Cytoplasm- ribosomes, granules, nucleoid/chromosome.
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Bacterial Appendages:• Pili (pl), pilus (s)
– Only found in gram negative bacteria– hollow, hairlike structures of protein larger and more sparse than
fimbriae. – allow bacteria to attach to other cells. – sex pilus, - transfer from one bacterial cell to another- conjugation.
• fimbriae (pl) fimbria (s)– Adhesion to cells and surfaces– Responsible for biofilms.– Pathogenesis of gonococcus and E.coli
• Flagella (pl), flagellum(s)– Motility- – long appendages which rotate by means of a "motor" located just under
the cytoplasmic membrane. – Bacteria may have one, a few, or many flagella in different positions on
the cell.– All spirilla, half of bacilli, rare cocci– Advantages- chemotaxis-positive and negative.
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Motility-
• Flagella vary in number and arrangement.• Polar arrangment-
– Monotrichious- 1 flagellum at one end• Fastest; Pseudomonas -example
– Lophotrichious- tuft at one end– Amphitrichious- bipolar
• Peritrichious-– Multiple flagella; randomly dispersed around the
bacterial cell– E.coli -example
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Structure of flagellaallows for 360 degree filament rotation
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Detection of Motility
1. Stab line in semisolid motility agargrowth out from the streak line indicates motility.
A= motile; B=nonmotile
2. Motility plate
3. Hanging drop- from actively
growing culture 18-24 hrs old.
directional movement
vs. “brownian movement
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Bacterial Surface Structure- cell envelope
Bacteria have some or all of the following structures:
1. Glycocalyx- capsule or slime layer–
layer of polysaccharide (sometimes proteins) – Different composition in certain bacteria-
• Streptococcus pneumoniae- capsule- tighter • Slime layer- looser, washes off
– protects the bacterial cell from phagocytosis– associated with pathogenic bacteria -Staphylococcus aureus.– Glycocalyx- colonize nonliving materials- plastics, catheters,
medical devices.
1. Cell wall –• peptidoglycan (polysaccharides + protein),• Support and shape of a bacterial cell.
The three primary shapes in bacteria are: » coccus (spherical),» bacillus (rod-shaped) » spirillum (spiral).» Mycoplasma are bacteria that have no cell wall and therefore
have no definite shape.
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2. Cell wall – peptidoglycan (polysaccharides + protein)
Repeating glycan chains (N acetyl glucosamine and N acetyl muramic acid) with crosslinked peptides.
Support and shape of a bacterial cell. The three primary shapes in bacteria are:
» coccus (spherical),» bacillus (rod-shaped) » spirillum (spiral).» Mycoplasma are bacteria that have no cell wall
and therefore have no definite shape.
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Differences in Cell Wall Structure
• Basis of Gram Stain Reaction– Hans Christian Gram- 1884
• Differential Stain• Gram Positive vs Gram Negative Cells• Gram Positive Cells-
– Thick peptidoglycan layer with embedded teichoic acids
• Gram Negative Cells-– Thin peptidoglycan layer, outer membrane of
lipopolysaccharide.
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Gram Stain Reaction
• Hans Christian Gram- 1880s• Divides bacteria into 2 main groups-
– Gram positive – Gram negative
• Also- gram variable• Gram nonreactive
• Gram positive bacteria– many layers of peptidoglycan and teichoic acids.– Form a crystal violet-iodine-teichoic acid complex
• Large complex,difficult to decolorize
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• Gram negative cells– Very thin peptidoglycan– No teichoic acids– Alcohol decolorizer readily removes the crystal violet.– Alcohol also dissolves the lipopolysaccharide of the cell wall.
• Gram variable cells– Some cells retain crystal violet; some decolorize and take up the
safranin– 4 factors-
• Genetics- variable amount of teichoic acid.• Age of culture- older cultures have variable amount of teichoic acid• Growth medium- necessary nutrients not available• Technique-
– smear not thin or evenly made.– Staining procedure not done correctly- decolorizer left on too long.
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• Gram nonreactive cells– Have peptidoglycan but have very waxy- thick
lipids –waterproof, dyes cannot enter either.– Examples- Mycobacterium- tuberculosis and
leprosy. • Alternative staining- acid fast stain-
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Cell wall deficient formsFigure 4.17
• L- forms ( Lister Institute where discovered)– Bacteria loses cell wall during the life cycle
• Result of a mutation in cell wall forming genes• Induced by treating with lysozyme or penicillin which disrupts
the cell wall
– Protoplast- • G + bacterium with no c. wall, only a c. membrane• Fragile, easily lysed
– Spheroplast-• G – bacterium loses peptidoglycan, but has outer membrane• Less fragile but weakened.
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Surface structures continued:
• Outer membrane – This lipid bilayer is found in Gram negative
bacteria and is the source of lipopolysaccharide (LPS) in these bacteria
– LPS is toxic and turns on the immune system.
– Not found in Gram positive bacteria.
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Cell membrane• Located just beneath cell wall• Very thin• Lipid bilayer, similar to the plasma membrane of
other cells. Transport of ions, nutrients and waste across the membrane
• Typical – 30-40% phospholipids– 60-70% proteins
• Exceptions- – Mycoplasma- sterols– Archaea- unique branched hydrocarbons
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MesosomeExtension of cell membrane
– Folding into cytoplasm – internal pouch– Increases surface area.
• Gram-positive bacteria-prominent• Gram negative bacteria- smaller,harder to see.• Functions-
– Cell wall synthesis– Guides duplicated chromosomes into the daughter
cells in cell division.
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Photosynthetic Prokaryotes
• Cyannobacterium- dense stacks of internal membranes with photosynthetic pigments.
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Functions of Cell Membrane
• Carries out functions normally carried out by eukaryote organelles.
• Site for energy functions• Nutrient processing• Synthesis• Transport of nutrients and waste• Selectively permeable• Most enzymes of respiration and ATP synthesis• Enzyme synthesis of structural macromolecules
– Cell envelope and appendages
• Secretion of toxins and enzymes into environment.
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Cell cytoplasm
• Encased by cell membrane
• Dense, gelatinous
• Prominent site for biochemical and synthetic activities
• 70-80% water- solvent
• Mixture of nutrients- sugar, amino acids, salts– Building blacks for cell synthesis and energy
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Bacterial chromosome• Singular circular strand of DNA• Aggregated in a dense area- nucleiod• Long molecule of DNA tightly coiled around
protein molecules.
• Plasmids-– Nonessential pieces of DNA
• Often confer protection- resistance to drugs– Tiny, circular– Free or integrated– Duplicate and are passed on to offspring– Used in genetic engineering
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Ribosomes
• Site of protein synthesis
• Thousands – Occurs in chains –polysomes
• 70S – 2 smaller subunits– 30S and 50S
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Inclusions
• If nutrients abundant- stored intracellularly
• Granules- – Crystals of inorganic compounds not enclosed
by membranes• Sulfur granules- photosynthetic• Polyphosphate- corynebacterium• Metachromatic- Mycobacterium
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Bacterial Internal Structures• Endospores
– inert, resting, cells produced by some G+ genera: Clostridium, Bacillus and Sporosarcina
• have a 2-phase life cycle:– vegetative cell – metabolically active and growing– endospore – when exposed to adverse environmental conditions;
capable of high resistance and very long-term survival» Features of spores- size, shape, location=identification
– sporulation -formation of endospores • hardiest of all life forms• Forms inside a cell- functions in survival • not a means of reproduction• withstands extremes in heat, drying, freezing, radiation and
chemicals
– germination- return to vegetative growth
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Endospores• Resistance linked to high levels of calcium and
dipicolinic acid• Dehydrated, metabolically inactive• thick coat• Longevity verges on immortality - 25,250
million years.• Resistant to ordinary cleaning methods and
boiling• Pressurized steam at 120oC for 20-30 minutes
will destroy
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Bacterial Shapes, Arrangements, and Sizes
• Variety in shape, size, and arrangement but typically described by one of three basic shapes:– coccus - spherical– bacillus – rod
• coccobacillus – very short and plump• vibrio – gently curved
– spirillum - helical, comma, twisted rod, • spirochete – spring-like
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Bacterial Shapes, Arrangements, and Sizes
• Arrangement of cells is dependent on pattern of division and how cells remain attached after division:– cocci:
• singles• diplococci – in pairs• tetrads – groups of four• irregular clusters • chains• cubical packets
– bacilli:• chains• palisades
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