Lecture 7 Flashcards
List the 4 types of bacteria showed on the first slide and their gram stains
Salmonella: Gram negative bacillus
Streptococcus: Gram positive cocci
Listeria: Gram positive Bacillus
Staphylococcus: Gram positive cocci
Individual cell shapes of bacteria
Spheres (coccus)
Rods (Bacillus)
Other shapes: Vibrio (crescent shape) and spiral
Describe Coccus
Individual cells may occur in various arrangements
coccus: Single cell, alone
Diplococcus: Two cells
Streptococcus: Many cells in a chain
Staphylococcus: Many cells in a cluster
Example of a diplococcus
Enterococcus sp.
- Clustering can be variable within species
Describe Bacillus
Bacillus: Single cell, alone
Streptobacillus: Many cells in a chain
Relationship between bacteria and its name
Many bacteria are named after their shape: Bacillus subtilis
However, bacterial shape is not a very good homologous trait for classification
Stains of Escherichia coli and Bacillus megaterium
Coli: Gram negative bacillus
Megaterium: Gram positive streptobacillus
Morphological features of bacterial cell
Plasma membrane and the bacterial cell wall
Capsule/slime layer
Flagella and pilus
Sub cellular compartments
Endospores
Fimbriae of bacteria
Hairlike appendages that help cells adhere to other cells or to a substrate
Capsule of bacteria
Sticky layer of polysaccharide or protein that can help cell adherence and/or evasion of a host’s immune system
Internal organization of bacteria
No nucleus or other membrane-bounded organelles; usually no complex compartmentalization
Flagella of bacteria
Structures used by most motile bacteria for propulsion; many species can move toward or away from certain stimuli
Cell wall of bacteria
Found in nearly all prokaryotes; structure differs in gram positive and gram negative bacteria
Circular chromosome of bacteria are
Often accompanied by smaller rings of DNA called plasmids
Pilus of bacteria
Appendage that facilitates conjugation
Plasma membrane
- Is a lipid bilayer made of fatty acids
Single fatty acid
A single fatty acid has a hydrophilic head and a hydrophobic tail
In water, the heads face the water while the tails hide from the water, facing each other. This forms the two layered structure of lipid bilayer
Fatty acids (phospholipid) and polarity
Hydrophilic (polar) head
Hydrophobic (non polar) tail
Plasma membrane as a barrier
- Permeability barrier
- Very small molecules can diffuse through plasma membrane freely (N2, CO2, O2)
Molecules that diffuse slowly or not at all through the membrane
- Some small molecules can diffuse slowly (H2O, glycerol, ethanol)
- Molecules larger than 3-4 carbons and charged molecules can not diffuse at all (Glucose, H+)
Peptidoglycan
Bacteria has a peptidoglycan cell walls
- Made of two types of sugars attached in a long, unbranched chain (backbone)
One of the sugars have a short peptide attached (3-5 amino acids)
Different peptidoglycan backbones can attach via their peptides cross-linking
Mesh structure
Many peptidoglycan backbone attach to each other to form a mesh structure
- Peptidoglycan exists outside the plasma membrane, surrounding the entire cell
How does peptidoglycan and plasma membrane work together
- Make cell wall stronger
- Pep Is rigid and gives mechanical strength to the cell walls. Has large openings and lets molecules diffuse freely due to it not having permeability
Plasma membrane is a permeability barrier but is not as mechanically strong
Peptidoglycan surrounds the
Plasma membrane
Osmotic pressure in bacteria
Concentration of chemicals in cytoplasm is higher compared to the surrounding environment - creates osmotic pressure for water to move from environment into cell. Cell will burst if too much water enters
Pep gives mechanical strength to cell envelope to prevent the bursting
Two types of bacterial cell wall
Gram positive cell wall
- Thick layer of peptidoglycan
- Relatively simpler structure
Gram negative cell wall
- Thin layer of peptidoglycan
- A second lipid bilayer surrounds the peptidoglycan layer (outer membrane)
Gram stain purpose
To stain gram positive and negative cells to appear different under a light microscope
Gram stain procedure
- Stain all cells with dark purple dye, crystal violet
- Destain with ethanol
- Gram negative cells become clear whereas gram positive remain purple because of thick pep - Stain again with lighter pink dye safranin
Gram positive cells appear purple
Gram negative cells appear pink
Examples of gram negative bacteria
E coli
Chlamydias
Spirochetes
Cyanobacteria
Gram positive bacteria
S.Aureus and B.subtillis
Staining gram negative does not always mean
The bacteria has a gram negative cell wall
- Some group such as chlamydias don’t have a peptidoglycan cell wall but still stain pink
Peptidoglycan is the target for
Many antibiotics (pencillin, vancomycin)
- Stopping petidoglycan synthesis stops bacterial growth
How does the effectiveness of antibiotics depend on the cell wall structure
Gram positive have peptidoglycan exposed to environment, antibiotics have easier access
Gram negative have outer membrane, blocking many antibiotics from accessing the peptidoglycan
Gram stain only takes
10 minutes to do
Capsule and slime layer
A layer outside the bacterial cell wall
Made of sugars and/or peptides (species dependent)
Can be rigid (capsule) or more soft and flexible (slime layer)
Resists dehydration, resists immune system of host organism, adherence to surfaces
Sub cellular structures
Do not have organelles
Can still have complex sub cellular structures made of lipid bilayers and protein shells such as thylakoid membrane and carboxysomes
Thylakoid membrane and Carboxysomes
Thylakoid
- Multiple folds of lipid bilayer inside cyanobacteria
- Conversion of light energy to chemical energy (ATP)
Carboxysomes
- Polygonal structures made of protein shell, found inside cyanobacteria
- Fixation of CO2 into organic molecules
Flagella
Long whip like structure attached to the bacterial cell wall
Rotation of flagella makes cell move
Very dissimilar structure from a eukaryotic flagella
- Analogous structures due to convergent evolution
Chemotaxis:
Bacteria has systems to move ‘towards good things’ and ‘away from bad things’
Fimbriae and pilus
Other string like structures are also found on bacterial surfaces
Fimbriae
- Shorter and more numerous
- Attachment to surfaces and to other cells
Pilus
- A long tubular structure
- Connects two bacterial cells to facilitate exchange of genetic material (form of horizontal gene transfer)
Endospores
Survival mechanism deployed by some gram positive bacteria
Can withstand huge amounts of stress such as UV radiation
Vegetative cells (normally growing cells) form endospores to survive unfavorable environmental condition
- Vegetative cells die in the unfavorable condition while the endospores persist
Endospores grow back to vegetative cells once
Environmental condition is restored
Would bacillus spores survive space travel and contaminate other planets
Only a fraction of bacillus endospores survived 1.5 years of exposure to outer space and were able to grow back into vegetative cells
PROTECT experiment by ESA
- Bacillus subtilis spores were loaded on a spacecraft
and delivered to the International Space Station on
February 7, 2008 - Bacillus spores were exposed to outer space for 1.5
years before they were brought back to earth
