growth and physiology 2 Flashcards
how pH salinity and temp extremes affect microbial growth on graph
- Increased lag
- Decreased slope
- Shorter plateau
- More rapid decline
- Less cells produced
PH - measure of acidity
Microbes have an optimum pH with decreased growth above and below that pH
Salinity - Concentration of salt – NaCl
6 points
- Effect on amount of free water – water activity (Aw)
- More solute dissolved and interacting with water the lower the Aw
- Normally Aw lower inside cell than outside so water flows inwards by osmosis
- If high salt concentration outside cell osmosis reversed
- Cells accumulate small molecules (compatible solutes) with no effect on cell metabolism. Counteracts water moving in.
- If salt concentration too high cells lose water, shrink, dehydrate - plasmolysis
temperature
- All have a minimum, optimum and maximum temperature for growth
what are the 4 main groups depending on their cardinal temperatures
- Psychrophiles 0-25 C
- Mesophiles 15-45 C
- Thermohiles 45-70 C
- Hyperthermophiles (extreme thermophiles) 70-110 C
Sterilisation - kill organisms and spores
Dry heat 1
heating in an oven at between 160-180 C for 2-4 hours.
Used for glassware, equipment but seldom for media or food.
Sterilisation - kill organisms and spores
Dry heat 2
heating in a bunsen flame.
Used for microbiological loops, etc.
Sterilisation - kill organisms and spores
moist heat
autoclaving using pressurised steam. At a pressure of 101 kPa
temperature of steam is 121 C.
Used for media and equipment, and food that is canned.
Can affect nutritional value, texture and taste.
Pasteurisation – not sterile
Temperatures below 100C.
Aim is to kill pathogens and reduce number of other organisms.
Does not destroy spores. Used for products damaged by heat.
Bacteria
cell membrane
Ester-linked fatty acids, protein
Bacteria
cell wall
Murein (peptidoglycan), lipopolysaccharide
archaea
cell membrane
Ether-linked isoprenoids, protein
archaea
cell wall
Protein, glycoprotein, pseudomurein, wall-less
Eukarya
cell membrane
Ester-linked fatty acids, protein, sterols
Eukarya
cell wall
Various, no peptidoglycan
5 features of Cell membranes
- Boundary of cell
- Separate internal aqueous, polar environment from external (usually) aqueous, polar environment
- Consist of lipid which is non-polar so acts as a barrier
- The membrane lipids have associated polar regions
- Arrange in sandwich so polar regions to interior and exterior of cell with non-polar region between
6 features of Cell membrane lipids
Fatty acids ester-linked to glycerol
- Two fatty acids with non-polar hydrocarbon chains
- Fatty acids are not branched
- One highly polar group including phosphate
- Called phospholipids or phosphoacylglycerols
- Arrange in a bilayer
- Found in Bacteria and Eukarya
4 features of archaea cell membrane
Isoprenoid chains ether-linked to glycerol
- Two non-polar branched isoprenoid chains
- One polar group
- Arrange in a bilayer if a diether
- Cross whole membrane if tetraether
importance of cell wall
5 points
- Cell walls provide rigid structure to prevent prokaryotic cells bursting
- Higher concentration of solutes inside cell than outside
- Osmosis causes water to move into cell
- Causes cell to swell
- Would burst in absence of cell wall
Peptidoglycan or murein
(Peptide chains linking polysaccharide)
[not sure if necessary to learn. leave]
5 points
- Tetra-peptide – 4 amino acids: L-alanine,D-glutamic acid, L-lysine or diaminopimelic acid (DAPA), D-alanine
- D-amino acids - not in proteins. DAPA only in some prokaryotic cell walls
- Penta-glycine peptide cross links between the tetra-peptide
- Polysaccharide – long polysaccharides with repeating two units [N-acetyl muramic acid (NAM) and N-acetyl glucosamine (NAG)]
- Murein – muramic acid and protein
Teichoic acids [not sure if necessary to learn. leave]
6 points
- Derivatives of polyalcohols - glycerol (3 x –OH) and polyribotol (5 x –OH)
- Terminal –OH link to phosphate groups which ionise to give -ve charges
- Sugars or alanine may attach to non-terminal –OH groups
- May chain
- Teichoic acids link to the NAM in peptidoglycan
- Also link to lipid in membrane – lipoteichoic acids
Outer membrane (found in some bacteria) looks like standard lipid bilayer but…
6 points
- Inner half contains a lipoprotein which links to peptidoglycan (called LPP) and phospholipids
- Outer half contains lipopolysaccharides (LPS)
- LPS composed of Lipid A and long polysaccharide chains extending to the outside of the cell
- Lipid A has 4 fatty acid chains linked to a glucosamine-phosphate complex
- Polysaccharide links to one of the glucosamines
- Important antigenic properties and may be toxic
Gram-positive and Gram-negative cell walls
2 points
- Bacteria can be divided into two groups on the basis of a stain called the Gram stain
- Difference depends on structure of cell wall
gram-positive cell walls
thick layer of peptidoglycan with teichoic acids and some surface proteins
gram negative cell walls
2 points
- thin layer of peptidoglycan with outer membrane containing lipopolysaccharide.
- Porin transport protein in outer membrane.
categorising
Direct observation
3 points
- Information about shape and
size of cells - Information about their staining characteristics
Gram +ve or Gram -ve - Information about shape, size, colour of colonies on agar plates
categorising
biochemical analysis
3 points
- chemical analysis of the organisms themselves:
Archaeal cell membranes contain lipids which are ether-linked whereas bacteria have ester-linked lipids
Some bacteria have an outer membrane containing lipopolysaccharides while some do not
- biochemical analysis of metabolic products:
Some bacteria produce lactic acid from glucose, yeasts produce ethanol from glucose
Some micro-organisms can release oxygen from hydrogen peroxide
- Carry out range of specific tests to obtain biochemical characteristics
categorising
How organisms are classified
- Phenotypic classification depends on the similarity of the observable characteristics of organisms
e. g. colony size, shape, colour; motility; rod or coccus; Gram-positive or Gram-negative; spores; biochemical parameters.
categorising
Molecular analysis
4 points
- Development of molecular biology techniques allows detailed information about genotypes (genetic characteristics)
- Sequencing of nucleic acids showed specific similarities and differences between taxonomic groups (Phyla)
- Used 16S ribosomal RNA to help understand evolutionary development
- Some reclassification of organisms as a result of molecular analysis
