Sofronio Agustin Professor LECTURES IN MICROBIOLOGY The Prokaryotes LESSON 4 Sofronio Agustin Professor

Lesson 4 Topics External Structures Cell Envelope Internal Structures Cell Shapes, Arrangement, and Sizes Classification

External Structures Flagella Pili and fimbriae Glycocalyx

Flagella Composed of protein subunits called flagellin. “H” antigens used in serotyping of bacterial strains. Example: Escherichia coli O157: H7

Three components of a flagellum: filament, hook and basal body Flagellar Structure Three components of a flagellum: filament, hook and basal body

Flagellar Arrangement (a) Monotrichous (b) Lophotrichous (c) Amphitrichous (d) Peritrichous

The rotation of the flagella enables bacteria to be motile. Bacterial Motility The rotation of the flagella enables bacteria to be motile.

Chemotaxis Chemotaxis is the movement of bacteria in response to chemical signals. It consists of a series of tumbles and runs toward or away from source of stimuli.

Endoflagella Spirochetes have their flagella embedded in the membrane = endoflagella Also called axial filament Example: T. pallidum (corkscrew motility)

Pili and Fimbriae Attachment Mating (Conjugation)

Fimbriae are smaller than flagella and are important for attachment.

Pili Pili enable conjugation to occur, which is the transfer of DNA from one bacterial cell to another (“mating”).

Glycocalyx Capsule Slime layer Protects bacteria from phagocytic cells Enable attachment and aggregation of bacterial cells

Capsule The capsule is covalently bound to the cell wall. Associated with virulence in bacteria. Example: Streptococcus pneumoniae

Slime Layer The slime layer is loosely bound to the cell. Carbohydrate rich material enhances adherence of cells on surfaces Example: Streptococcus mutans and “plaque formation”

Biofilms The slime layer is associated with cell aggregation and the formation of biofilms Example: Staphylococcus epidermidis biofilms on catheter tips

Cell Envelope Cell wall Cytoplasmic membrane Cell wall-less bacteria Gram-positive Gram-negative Cytoplasmic membrane Cell wall-less bacteria

Cell Wall Gram positive cell wall Gram-negative cell wall Thick peptidoglycan (PG) layer Acidic polysaccharides Teichoic acid and lipoteichoic acid Gram-negative cell wall Thin peptidoglycan (PG) layer Lipopolysaccharide layer Porins Periplasmic space

Peptidoglycan Layer PG is a complex sugar and peptide structure important for cell wall stability and shape.

Structures associated with gram-positive and gram-negative cell walls. Cell Wall Structures Structures associated with gram-positive and gram-negative cell walls.

Cytoplasmic Membrane Phospholipid bilayer “Fluid mosaic” model Embedded proteins for active transport Enzymes for energy generation Photosynthetic pigments

L Forms Mutations can cause some bacteria to lose the ability to synthesize the cell wall and are called L forms.

Cell Wall Less Bacteria No peptidoglycan layer Cell membrane contains sterols for stability

The Mycoplasma Mycoplasma bacteria have no cell wall, which contributes to their pleomorphic shapes Smallest bacteria (0.2 um) Example: Mycoplasma pneumoniae (SEM on right)

Internal Structures Cytoplasm Genome Inclusion bodies Actin Endospore

Cytoplasm Gelatinous solution containing water, nutrients, proteins, and genetic material Site for cell metabolism

Genetic Structures Deoxyribonucleic acid (DNA) Ribonucleic acid (RNA) Ribosomes

Bacterial Genome Most bacteria contain a single circular double strand of DNA called a nucleoid.

Prokaryotic Ribosome A ribosome is a combination of RNA and protein, and is the site for protein synthesis Composed of large (50S) and small (30S) subunits S = Svedverg unit, measures molecular size

Inclusion Bodies Inclusion bodies enable a cell to store nutrients and to survive in nutrient depleted environments

Bacterial Cytoskeleton Actin is a protein fiber present in some bacteria, which is involved in maintaining cell shape.

Endospores Nutrient depletion induces some bacteria (vegetative cell) to form endospores in order to survive Dehydrated gel state due to calcium-protein complex Dipicolinic acid (found only in spores) hardens the spore

Endospore Formation Some pathogenic bacteria that produce toxins during the vegetative stage are capable of forming spores. (e.g. Bacillus and Clostridium species)

Bacterial Morphology Coccus Rod or bacillus Curved or spiral Cell arrangements Pleomorphism

Typical Shapes and Arrangements Scanning electron micrographs of different bacterial shapes and arrangements. (a) Streptococcus (b) Bacillus (c) Spirochete (d) Spirillum

Pleomorphism Some bacteria show varied shapes and arrangements called pleomorphism. Ex: Corynebacterium diphtheriae’s “Chinese letter” arrangement.

Bacterial Shapes and Arrangements Cellular shapes and arrangements are useful in bacterial identification.

The Dimension of Bacteria Relative size of a bacterial cell compared to other cells including viruses.

Classification Phenotypic methods Molecular methods Taxonomic scheme Unique groups

Phenotypic Methods Cell morphology - staining Biochemical test – enzyme test

Molecular Methods DNA sequence 16S RNA Protein sequence

Major Taxonomic Groups of Bacteria The methods of classification have allowed bacteria to be classified into different taxonomic groups Re: Bergey’s Manual of Determinative Bacteriology (Table on right)

Unique Bacterial Types Intracellular bacteria Photosynthetic bacteria Sulfur bacteria Gliding and fruiting bacteria

Intracellular Bacteria Intracellular bacteria must live in host cells for them to metabolize and reproduce Examples: Rickettsiae and Chlamydiae

Cyanobacteria Cyanobacteria are important photosynthetic bacteria associated with oxygen production.

Sulfur Bacteria Green and purple sulfur bacteria are photosynthetic, do not give off oxygen, and are found in sulfur springs, freshwater, and swamps.

Myxobacteria An example of a fruiting body bacteria in which reproductive spores are produced.

Archaea Associated with extreme environments Contain unique cell walls Contain unique internal structures

Archaea Archaea are found in: hot springs (thermophiles) high salt content areas (halophiles) Example: Halobacterium salinarium