LECTURES IN MICROBIOLOGY. The Prokaryotes. Sofronio Agustin Professor. LESSON 4. Lesson 4 Topics. External Structures Cell Envelope Internal Structures Cell Shapes, Arrangement, and Sizes Classification. External Structures. Flagella Pili and fimbriae Glycocalyx. Flagella.
Three components of a flagellum: filament, hook and basal body
(a) Monotrichous (b) Lophotrichous (c) Amphitrichous (d) Peritrichous
The rotation of the flagella enables bacteria to be motile.
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.
Fimbriae are smaller than flagella and are important for attachment.
Pili enable conjugation to occur, which is the transfer of DNA from one bacterial cell to another (“mating”).
Protects bacteria from phagocytic cells
Enable attachment and aggregation of bacterial cells
Streptococcus mutans and “plaque formation”
Staphylococcus epidermidis biofilms on catheter tips
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.
Mutations can cause some bacteria to lose the ability to synthesize the cell wall and are called L forms.
(SEM on right)
Most bacteria contain a single circular double strand of DNA called a nucleoid.
Inclusion bodies enable a cell to store nutrients and to survive in nutrient depleted environments
Actin is a protein fiber present in some bacteria, which is involved in maintaining cell shape.
Some pathogenic bacteria that produce toxins during the vegetative stage are capable of forming spores. (e.g. Bacillus and Clostridium species)
Scanning electron micrographs of different bacterial shapes and arrangements.
(a) Streptococcus (b) Bacillus (c) Spirochete (d) Spirillum
Some bacteria show varied shapes and arrangements called pleomorphism. Ex: Corynebacterium diphtheriae’s “Chinese letter” arrangement.
Cellular shapes and arrangements are useful in bacterial identification.
Relative size of a bacterial cell compared to other cells including viruses.
(Table on right)
Cyanobacteria are important photosynthetic bacteria associated with oxygen production.
Green and purple sulfur bacteria are photosynthetic, do not give off oxygen, and are found in sulfur springs, freshwater, and swamps.
An example of a fruiting body bacteria in which reproductive spores are produced.