Basic Bacteriology

BacteriaBacteria are single-celled organisms

Contain no membrane bound nucleusTermed prokaryotes = pre nucleus

Pro = prekaryote = nucleus

Do not contain any other organelles (such as ER or Golgi or mitochondria)

Cytoplasm is surrounded by a lipid membrane with is surrounded by a rigid cell wall

DNA bundled in a region called the nucleoid

Flagella

Ribosomes

Capsule

Cell wall

Plasmamembrane

Nucleoid region (DNA)

Pili

The Bacterial Cell

The Bacterial CellNucleoid DNA

Bacterial NomenclatureBinomial naming system

Two word naming systemFirst word is genus name

Always capitalizedEscherichia

Second word is species nameNot capitalized

coliWhen writing full name genus usually

abbreviatedE. coli

Full name always italicizedOr underlined

Bacterial Morphology

Morphology classification by shapeMorphology is often expressed in the

binomial naming systemEx. Bacillus subtillis, the word Bacillus means

rodEx. Streptococcus pyogenes, Streptococcus

means a chain of spheresEx. Helicobacter pylori, helix shaped bacteriumMany names of bacteria do not reference there

shape such as E. coli, Pseudomonas aeruginosa, or Burkholdaria cepacia.

Bacterial Morphology

Examples of Morphology

• Bacteria exhibit a variety of shapes

• Coccus• Spherical

• Bacillus• Rod or

cylinder shaped

Examples of Morphology

• Other shapes• Coccobacillus

• Short round rod

• Vibrio• Curved rod

• Spirillum• Spiral shaped

• Spirochete• Helical shape

Bacterial Anatomy and Structures

Cytoplasm- fluid that fills the cell where most reactions and activities of the cell take place

Cell Membrane- barrier between the internal cell fluid (cytoplasm) and the exterior environment. It is selectively permeable only allowing in selected comounds

Cell Wall- rigid structure surrounding the cell membrane that gives bacteria there shape. Stronger than the cell membrane helps hold the cell together and maintain structural integrity. The cell wall can be of varying degrees of thickness depending on the type of bacteria

Cell capsule- slime layer that protects bacteria and helps bacteria to adhere to surfaces

Bacterial Anatomy and Structures

Nucleoid region- location of the genetic material (DNA) in the bacterial cell. Typically bacterial DNA is one large circular DNA molecule that is packed together by supercoiling.

*Bacterial DNA should not be referred to as a chromosome because it is not packed together using chromatin and does not resemble the organization of DNA in eukaryotes. The alternate name for bacterial DNA is genophore

Plasmid- a small genetic element of circular DNA that is separate and distinct from the nucleoid DNA. The plasmid is typically thousands of times smaller than the nucleoid DNA but often very important as it may carry genes for antibiotic drug resistance

Bacterial Anatomy and Structures

Flagella- long structure made of protein that propels the bacteria when it spins.

Pili- structure made of protein subunits that extend out of the cell. Function for attachment to surfaces and gliding motility.

Inclusions- small structure used to store excess material typically as nutrient reserve. Stored materials include phosphates, polysaccharides, nitrogen, sulfur, proteins and biopolymers

Ribosome- a structure consisting of protein and rRNA. It translates mRNA into a sequence of amino acids (proteins)

Size Distribution

Size in the Microbial World

Tremendous range in sizeSmallest virus approximately 1/1,000,000th size of

largest eukaryotic cell

Prokaryotic CellsComparing Prokaryotic and Eukaryotic

CellsProkaryote comes from the Greek words

for prenucleus.Eukaryote comes from the Greek words

for true nucleus.

One circular chromosome, not in a membrane

No histonesNo organellesPeptidoglycan cell

wallsBinary fission

Prokaryote Eukaryote

Paired chromosomes, in nuclear membrane

HistonesOrganellesPolysaccharide

cell wallsMitotic spindle

Average size: 0.2 -1.0 µm 2 - 8 µmBasic shapes:

Unusual shapesStar-shaped StellaSquare Haloarcula

Most bacteria are monomorphicA few are pleomorphic

Figure 4.5

Pairs: diplococci, diplobacilli

Clusters: staphylococci

Chains: streptococci, streptobacilli

Arrangements

Outside cell wallUsually stickyA capsule is neatly

organizedA slime layer is

unorganized & loose

Extracellular polysaccharide allows cell to attach

Capsules prevent phagocytosis

Glycocalyx

Figure 4.6a, b

Outside cell wallMade of chains of

flagellinAttached to a

protein hookAnchored to the

wall and membrane by the basal body

Flagella

Figure 4.8

Flagella Arrangement

Figure 4.7

Figure 4.8

Rotate flagella to run or tumbleMove toward or away from stimuli (taxis)Flagella proteins are H antigens

(e.g., E. coli O157:H7)

Motile Cells

Motile Cells

Figure 4.9

EndoflagellaIn spirochetesAnchored at one

end of a cellRotation causes

cell to move

Axial Filaments

Figure 4.10a

Fimbriae allow attachment

Pili are used to transfer DNA from one cell to another

Figure 4.11

Prevents osmotic lysisMade of peptidoglycan (in bacteria)

Cell Wall

Figure 4.6a, b

Polymer of disaccharideN-acetylglucosamine (NAG) & N-acetylmuramic acid (NAM)

Linked by polypeptides

Peptidoglycan

Figure 4.13a

Figure 4.13b, c

Thick peptidoglycan

Teichoic acidsIn acid-fast

cells, contains mycolic acid

Gram-positive cell wallsGram-negative cell walls

Thin peptidoglycan

No teichoic acidsOuter membrane

Teichoic acids:Lipoteichoic acid links to plasma membraneWall teichoic acid links to peptidoglycan

May regulate movement of cationsPolysaccharides provide antigenic variation

Gram-Positive cell walls

Figure 4.13b

Lipopolysaccharides, lipoproteins, phospholipids.Forms the periplasm between the outer

membrane and the plasma membrane.Protection from phagocytes, complement,

antibiotics.O polysaccharide antigen, e.g., E. coli O157:H7.Lipid A is an endotoxin.Porins (proteins) form channels through

membrane

Gram-Negative Outer Membrane

Gram-Negative Outer Membrane

Figure 4.13c

Crystal violet-iodine crystals form in cellGram-positive

Alcohol dehydrates peptidoglycanCV-I crystals do not leave

Gram-negativeAlcohol dissolves outer membrane and leaves

holes in peptidoglycanCV-I washes out

Gram Stain Mechanism

MycoplasmasLack cell wallsSterols in plasma membrane

ArchaeaWall-less, orWalls of pseudomurein (lack NAM and D amino

acids)

Atypical Cell Walls

Lysozyme digests disaccharide in peptidoglycan.Penicillin inhibits peptide bridges in

peptidoglycan.Protoplast is a wall-less cell.Spheroplast is a wall-less Gram-positive cell.L forms are wall-less cells that swell into

irregular shapes.Protoplasts and spheroplasts are susceptible to

osmotic lysis.

Damage to Cell Walls

Plasma Membrane

Figure 4.14a

Plasma Membrane

Phospholipid bilayerPeripheral proteinsIntegral proteinsTransmembrane proteins

Figure 4.14b

Membrane is as viscous as olive oil.

Proteins move to function

Phospholipids rotate and move laterally

Fluid Mosaic Model

Figure 4.14b