Classification of bacteria (cell wall + environmental factors) Flashcards
What is the main component of the bacteria cell wall
peptidoglycan
What is the differences between gram +ve and gram -ve bacteria
Gram +ve bacteria has 90% of the cell wall being peptidoglycan + high amts of teichoic acid
Gram -ve bacteria has 10% of the cell wall being peptidoglycan + additional outer membrane called lipopolysaccharide (LPS)
What is the procedure of gram staining
Crystal violet for 30s + tilt off
iodine for 60s + rinse with water
Ethanol treatment + rinse with water
Safranin for 60s + rinse with water
What is the purpose of crystal violet + iodine in gram staining
Crystal violet: To affix the violet dye
Iodine: to ensure the violet dye complex forms inside cells
What is the purpose of ethanol in gram staining
In gram +ve bacteria, alcohol dehydrates thick peptidoglycan layer, trapping the dye complex.
In gram -ve bacteria, alcohol washes the colour away, leaving the cells colourless.
How are bacteria classified according to pH?
Acidophile: pH 0 - 5.5
Neutrophile: pH 5.5 - 8
alkaliphile: pH 8 - 11.5
most bacteria are neutrophiles
Acidophiles can cause serious environmental problems but they can recover some metals
What is the purpose of safranin in gram staining
Gram +ve bacteria will still be purple as red dye has no effect
Gram -ve bacteria will be stained red as the safranin stains the colourless cell
Why can bacteria tolerate certain ranges of temperatures?
If too cold, kinetic energy is lower -> chemical reactions are slower, so transport processes and cell metabolism would be slower
If too hot, proteins denature as hydrogen bonds keep the shape of the protein break down, membranes are destroyed and cell dies
How are bacteria classified according to temperature
Psychrophile: cold temps like 4 ℃
Mesophile: moderate temps like 36 ℃
thermophile: hot temps like 60 ℃
hyperthermophile: hotter temps like 120 ℃
Why cant some bacteria do aerobic respiration
Dont have enzymes to carry out aerobic respiration
Harmful byproducts could be made and the bacteria might not be able to break those down
How are bacteria classified according to their oxygen requirements? (first 2)
(refer to slides for visualisation of cells)
Obligate aerobe: MUST require oxygen
relies on oxygen as electron receptor to generate energy
Facultative anaerobe: can grow WITH or WITHOUT oxygen
carries out aerobic / anaerobic respiration when oxygen / no oxygen is present
But grows better WITH oxygen
How are bacteria classified according to their oxygen requirements? (last 3)
(refer to slides for visualisation of cells)
Aerotolerant anaerobe: cannot use oxygen but can tolerate its presence
can protect itself from oxygen / has enzymes that can break down harmful byproducts of aerobic respiration
grows equally well in both presence and absence of oxygen
Strict anaerobes: CANNOT grow WITH oxygen present
Carries out anaerobic respiration mtds (fermentation)
microaerophile: requires oxygen for aerobic respiration (only needs a lower lvl of oxygen)
How to grow anaerobes
Using smth called GasPak
A container with reagents to create a controlled environment
The envelope inside releases H2 and CO2 after adding water to create an anaerobic environment (CO2 promotes more rapid growth of these microorganisms)
Oxygen is removed from the chamber by combining hydrogen to form water (reaction is using palladium pellets as a catalyst)
Methylene blue indicator is used to indicate the presence oxygen, which will be colourless if there is NO oxygen
How to test if bacteria can aerobic respiration
Using Oxidase test!
Tests for the presence of Cytochrome C (important for electron transport chain)
if positive, bacteria can use O2 as electron recipient (positive reaction wld turn filter paper dark purple)
even if positive, does not mean that bacteria is obligate aerobe.
how to test if bacteria can break down by products
Using catalase test!
Breaks down hydrogen peroxide into water and oxygen gas
Hydrogen peroxide is a harmful byproduct of aerobic respiration
When adding hydrogen peroxide to culture, if there are bubbles its catalase +ve. If no bubbles its catalase -ve
