Microbial Growth Flashcards
Macronutrients
required in large amounts- C,N,H,O,P,S,K,Mg,Ca,Na
Micronutrients
required in trace amounts
Fe, trace metals
Growth factors
vitamins, AA, organic molecules the organism cant synthesize itself
Reproduction
Binary fission: the cell grows in size until it forms a partition, septum, that constricts the cells into two daughter cells
clones, one copy of chromosome, sufficient ribosomes etc.
Steps: cell elongation, septum formation, formation of walls/cell separation
growth of population
increase in the number of cells or biomass
Requirements for cell division
*synthesis of new cell wall material
destruction by *autolysins
Bactoprenol allows peptidoglycan subunit to be exported across cytoplasmic membrane
*Bactoprenol
allows peptidoglycan subunit to be exported across cytoplasmic membrane
wall bands
scar between old and new peptidoglycan
autolysins
create some gaps in peptidoglycan allowing rearrangement of the peptidoglycan and synthesis of a new cell wall
MacConkey
selective medium gram - grow bile salts - NO gram + Lactose fermenters: pink lactose non-fermenters: colorless
Mannitol-salt
selective medium
high NaCl: inhibits most gram- and many gram +
mannitol fermenters: yellow
non mannitol fermenters: pink
why count bacteria
evaluate contamination of food or water
efficiency of antimicrobial agents
study microbial populations from different ecosystems
Serial dilution
used to count the amount of bacterial cultures
enumerating bacteria
viable counts: reliable - 30-300 colonies
microscopic counts (define pros and cons)
counting chamber with a square grid.
count all cells: dead, alive, and cells that cannot be grown in lab
pros: fast no need to wait until bacteria has grown
cons: small cells can be missed, motile cells are hard to count and must be immobilized
Flow cytometry
cells pass through in single file. Flourescent dyes in stained cells are detected. - can label specific cell type/species.
Used to sort cells according to size, shape, labeling etc
Example: test for which cells are dead or alive
Turbidimetric method
Light is passed through a prism and filter into a sample containing cells, which scatter the light and a photocell measures the unscattered light.
Measures both living and dead cells, affected by properties of cells: size, clumping
*Generation time
time needed for the population to double
Depends on: growth medium, conditions
When the conditions are right, microorganisms can grow exponentially. The population doubles at a constant rate
Population growth and Generation time formula
N = N02^n N = number of cells N0 = initial number of cells n = generation number
g = t/n t = time
Growth phases
lag phase
exponential phase
stationary phase
death phase
lag phase
time needed by the bacteria to adjust to the new conditions, slow growth
exponential phase
doubling of the population at a constant rate
stationary phase
limiting nutriens are depleted or accumulation of a waste product that inhibits growth. Growth has stopped.
No net increase in cell number
death phase
cells start to die, metabolism has stopped, cell lysis may occur - also exponential
continuous culture
over time, most environmental systems can reach an equilibrium: cell division = cell death
*chemostat
fresh medium: supply of limiting nutrients
overflow: death of microorganism
Used to keep the microorganisms in a constant growth rate over a long period of time
Parameters: concentration of a limiting nutrient, dilution rate - addition of fresh medium
** once equilibrium is reached, number of cells is constant. The growth rate equals the death rate (*washout)
factors that affect growth
nutrients temp pH osmolarity oxygen pressure radiation
**extremophiles
microorganisms that prefer extreme conditions
**Psychrotolerant
organisms that can grow at 0C, but have optima around 20-40C
**Barophilic (piezophilic)
grow best at high pressure
Temperature of a hydrothermal vent??
350C
they have high temp and high pressure
*halophile
microorganisms that can grow at high salt concentrations
aerotolerant anaerobes
can grow in presence of oxygen but do not use it
obligate anaerobes
inhibited or killed by oxygen
