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= NegativeEscherichia 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 -