BIOLOGY OF BACTERIA
LAST DAY
• Brief introduction to bacteria, Archaebacteria,
and bacterial culturing media.
TODAY
• We will start by looking at our cultures, and providing
colony descriptors.
• We will learn about the Biology of Bacteria
• Bacteria structure
• Bacterial shapes
• We will look at microscopes again to observe bacterial
shapes under the microscope
BIOLOGY OF BACTERIA
• Part 1: Bacterial Cell structure
• Table 24-2 in your text book.
• Bacteria typically are composed of a cell wall, cell
membrane, and a cytoplasm.
• Some bacteria have distinctive structures that serve as a
protective layer (endospores, capsules, outermembranes)
BACTERIAL CELL WALL
• Both Archaebacteria and Eubacteria have cell walls
• Eubacterial cell walls are made of a molecule known as
PEPTIDOGLYCAN
• Peptidoglycan is a polymer consisting of sugars and
amino acids, which forms a mesh like barrier outside the
bacterial plasma membrane
• Gram Negative bacteria have an outer membrane
protects peptidoglycan, meaning some antibiotics are
ineffective against GN bacteria.
CELL MEMBRANE AND CYTOPLASM
• In Bacteria, cell membrane carries out cellular respiration
(metabolism of bacteria; producing energy) in absence of
mitochondria (like in eukaryotes)
• Unlike Eukaryotes, bacteria DO NOT CONTAIN MEMBRANE
BOUND ORGANELLES (i.e. no nucles, no golgi apparati, no
mitochondria)
• Cytoplasm consists mainly of Ribosomes and DNA
• Bacterial DNA is arranged in a single closed loop
• Aside from the main chromosome, Bacteria also have plasmids,
which are self replicating loops of DNA
CAPSULE AND PILI
• Many bacterial species produce an outer covering called a
capsule
• Protects cell from drying, harsh chemicals and immune
cells
• Glycocalyx:
• Fuzzy, sticky capsule around bacteria which allows it to
attach to host cell and tissue
• Pili
• Short protein projections on surface of bacteria, which aid
in attachment/adherence to host cells
ENDOSPORE
• Dormant structure produced by some Gram Positive
bacteria
• Thick outer covering that surrounds bacterial DNA
• Not reproductive cells, they allow bacteria to survive
harsh environmental conditions
• When conditions become favourable, the living
bacteria will emerge and continue multiplying
• Formed by the genera Bacillus and Clostridium
BACTERIAL MOVEMENT
• Typically propelled by a flagella
• Protein structures, which turn and propel the bacteria in an
erratic “run and tumble” motion
• Bacteria can have a single flagellum, a tuft of flagella at one
end, flagella at both ends, or flagella completely surrounding
the cell
• Some bacteria can mobilize by sliding on a slime layer they
produce (myxobacteria) or move in a corkscrew like motion
(spirilla)
INTRO TO BACTERIAL SHAPES AND
CLASSIFICATION
• Most bacteria have three basic shapes:
• Bacilli (rod shaped)
• Cocci (spherical/circular)
• Spirilla (corkscrew shaped)
BACILLI
• Rod shaped bacterium
COCCI
• Circular/spherical shaped bacteria
• Streptococci (chains)
Staphylococci (clusters)
Diplococci (dual)
SPIRILLA
• Corkscrew shaped
GRAM POSITIVE V GRAM NEGATIVE
• Bacteria are typically classified as either Gram Positive or
Gram Negative based on their color following the Gram
staining procedure
GRAM POSITIVE BACTERIA
• Appear purple under the microscope following a Gram stain
• Crystal Violet stains the Peptidoglycan on GP cell wall
• Remember PurPle = Positive
Staphylococcus aureus
GRAM NEGATIVE BACTERIA
• Appear pink following Gram stain
under microscope
• GN cells are protected by an outer
membrane which prevents the
peptidoglycan from being stained.
• The counterstain Saffranin gives GN
cells the pink colour
• Remember piNk= Negative
Escherichia coli
TO DO NOW
• Observe some of the different bacterial shapes
around the classroom
• Draw them on a blank sheet of paper
• Make sure to label whether they are cocci, bacilli or
spirilla, and Gram + or Gram -