Transcript Bacterial Form and Function

Bacterial Form and Function
• Microbiology- Ch. 4 pp 87-101
Structure of a Prokaryotic Cell
Prokaryote Structures:
1. Appendages- flagella, pili, fimbrae
2. Cell envelope- glycocalyx, cell wall , cell
membrane
3. Cytoplasm- ribosomes, granules,
nucleoid/chromosome.
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.
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
Structure of flagella
allows for 360 degree filament rotation
Flagellar arrangements
Detection of Motility
1. Stab line in semisolid motility agar
growth 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
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.
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.
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.
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
• 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.
• 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-
Cell wall deficient forms
Figure 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.
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.
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
Mesosome
Extension 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.
Photosynthetic Prokaryotes
• Cyannobacterium- dense stacks of
internal membranes with photosynthetic
pigments.
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.
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
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
Ribosomes
• Site of protein synthesis
• Thousands
– Occurs in chains –polysomes
• 70S
– 2 smaller subunits
– 30S and 50S
Inclusions
• If nutrients abundant- stored intracellularly
• Granules– Crystals of inorganic compounds not enclosed
by membranes
• Sulfur granules- photosynthetic
• Polyphosphate- corynebacterium
• Metachromatic- Mycobacterium
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
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
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
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