Microbial growth Flashcards
What are growth factors?
Organic molecules that the microorganisms need for growth but cannot synthesize by itself. Some growth factors are the by-product or waste of another microorganism.
Exemple of growth factors?
Vitamins, a.a. , purines, pyrimidines or other…
What are siderophores?
Shuttles to get iron. Molecule that will bidn to iron
What form or Iron can be taken up by cells? In what condition?
Ferrous ( 2+) or soluble form , in anoxic condition
What form of Iron cannot be taken up by cells? In what condition?
Ferric (3+) or insoluble. In oxic conditions.
What particular nutrient is limiting nutrient in nature and really important for many enzymes in resp. and photosynth?
IRON
What is growth of a population?
Increase in number of cells or in biomass
Most prokaryotes multiply by…
Binary fission
Steps of binary fission?
- CEll elongation
- Spetum formation
- Completion of septum, formation of walls, cell separation
What enzyme is involved in division of bacteria with peptidoglycan?
Autolysin and Bactoprenol
What is the role of Autolysin?
Destruction of peptidoglycan
What is the role of Bactoprenol?
Allows peptidoglycan subunits to be exported across the cytoplasmic membrane
What will decide where there has to be a fission/ making new peptidoglycan in division of bacteria?
FtsZ ring, or division ring
What is a wall band?
Scar between old and new peptidoglycan
Why is macconkey plate selective?
Because bile salts inhibits growth of Gram +
Why is MacConkey differential?
Because it contains lactose, and a pH indicator: only bacteria fermenting lactose will produce acid–> indicator = pink color on the plate
What does E.Coli form on a macconkey plate?
Dark pink colonies with bile precipitate: “ I don’t care about bile, I will destroy it”
Why is Manitol-salt selective?
Hight in NaCl concentration–> inhibits growth of most Gram -, and many Gram +
Why is mannitol-salt plates differential?
Mannitol fermenters will turn yellow
Exemple of a mannitol fermenter?
Straphylococcus aureus
Name all methods to measure microbial growth/presence.
- Viable Count
- Serial dilution
- Microscopic counts
- Flow cytometry
- Turbidimetric method
Describe viable count method
- Spread-plate method
- Pour plate method
- Need a permissive growth medium
- Results are reliable when there are between 30-300 colonies
How can you get a viable count with serial dilution?
CFU calculation: number of colonies/ dilution plated x volume plated
Microscopic count ?
- Use of a petroff-hauser chamber
- Count all cells, dead or alive…
- Can use viability staining to differenciate dead or alive
- Small cells can be missed.. motily, immobilize
Flow cytometry?
- Better at counting big cells : protozoans, yeast, mammalian cells etc.
- need of a DYE!
- Detection of dye allow labelling of sepcific cell types pr species
- Can be used to sort cells according to size/shape
turbidity method ?
- Measure alive or dead cells
- Can be affected by clumping or attachment to surface of cells
- Optical density is affacted by size, shape composition cell inclusion etc.
- Curve compare relationship between OD and cell number
What is generation time?
- Time needed for the population to double
On what do generation time depend?
- Growth medium
- Conditions
How to calculate the number of cells?
N= N0*2^n
N= number of cells N0= Number of cells initially n= number of generation (number of time doubled)
How to calculate generation time?
g=t/n
g= generation time
t=time
n= number of generation
What are the steps of a growth cycle in a batch culture (in a tube)?
- Lag phase: Time needed to ADJUST to new condition, SLOW growth
- Exponential phase: DOUBLING of the population at a constant rate
- Stationary phase: limiting nutrients are depleted or accumulation of a waste product that inhibits growth. GROWTH IS STOPPED. SURVIVAL PHASE.
- Death phase: Cells start to die, metabolism has stopped. EXPONENTIAL.
Particularity of batch culture?
CLOSED SYSTEM
-Affected by the metabolic activities of the growing microorganism: depletion of nutrients, generation of toxic waste.
What is a continuous culture?
- OPEN SYSTEM
- Reaches EQUILIBRIUM:
division rate= death rate - constant supply of nutrients
- constant diffusion of waste
What are factors affecting growth of organisms?
- Nutrients
- Temperature
- PH
- Radiation
- Oxygen
- Osmolarity
- Pressure
What do we call organisms that grow preferentially under extreme conditions?
Extremophiles
What are the 3 points on the curve of temperature affecting growth?
- Minimum: membrane gelling, transport processes are slowed down, so that growth is not possible
- Optimum: enzymatic reaction occuring at maximal rate
- Maximum: denaturation of enzymes , collapse of the cytoplasmic membrane, thermal lysis
How do we call organisms growing from -X-10 degres?
phsychrophiles
How do we call organisms growing best at 39?
Mesophiles
How do we call organisms growing best at 60 degres?
Thermophiles
How do we call organisms growing best at higher than 60 degres?
Hyperthermophiles
What are adaptations made by organisms that live in COLD environment?
- Changes in PROTS STRUCTURE
- Modification of the CYTOPLASMIC MEMBRANE so its stays more FLUID.
- COLD-SHOCK PROTEINS which help keep proteins stay active
- CRYOPROTECTANTS (antifreeze proteins ), glycerols help prevent the formation of ICE CRYSTALS that could puncture the cytoplasmic membrane
Does cold kill microorganisms?
No! ice crystals do!
How are microbial cultures preserved?
at -80 to -196 in liquid nitrogen
How do we call organisms that grow best at high pressure?
Barophilic organisms
What are adaptations made by organisms that live in HOT environment?
- Change in protein sequences so that enzymes are not denatured
- Modification of cytoplasmic membrane so it remains more RIGID (ex: lipid monolayer of archeas)
- HEAT-SHOCK proteins which help keep prots in active formation
- Protection mechanisms to ensure stability of DNA (GC rich –> 3 links)
Does hot temperatures kill microorganisms
yes! –> THERMAL LYSIS
What are adaptations made by organisms that live in LOW PH environment?
- changes in cytoplasmic membrane to resist HIGH CONCENTRATION PROTONS.
- usually, membrane requires high concentration of protons for stability. Bacteria lyse at high pH because membrane is unstable
What are adaptations made by organisms that live in HIGH PH environment?
- changes in cytoplasmic membrane to resist low concentration protons
- Use of Na+ gradient for transport motility
- ## Keep the electron transport chain close to th ATPase, so p+ that are pumped out do not diffuse away
What is internal pH?
- DNA= acid-labile
- RNA = alkali-labile
- Internal pH limits= 4.6- 9.5 (with protection systems not fully understood yet)
What is used to keep the pH steady in a growth medium and why?
Buffer, because waste can often affect pH (ex: MacConkey)
What do we call microorganisms that can grow in high salt concentration?
Halophiles
What is the % of salt in sea water?
3%
What are the groups of aerobes? and what is their metabolism?
- Obligate (oxygen required): aerobic respiration
- Facultative (not required, but growth is better): aerobic or anaerobic respiration
- Microaerophilic ( require oxygen but at low level) : aerobic respiration
What are the groups of anaerobes?
- Aerotolerant (do not require oxygen , and growth is not affected) : fermentation
- Obligate (oxygen is harmful/lethal) : fermentation or anaerobic respiration
What adjustment to the medium needs to be made for obligate and facultative aerobes to grow?
- Liquid medium
- Needs to be shaken constantly, so sufficient amount of oxygen present in medium.
What is added to a liquid medium to know the oxic zone, and how does in work?
Thyoglycolate. Reduces O2 to H2O. , creating a gradient of oxygen concentration.
What is the danger with toxic forms of oxygen?
They oxidize cell components, stopping key metabolic pathways and destroying key structures.
What compound can reduce O2 to O2-?
Flavoproteins, quinone, iron sulfur proteins
What enzymes are used to take care of toxic forms of oxygen , and in what types of aerobes?
Catalase and superoxide dismutase. They are present in aerobes and facultative aerobes.